Shalley Sharma - Academia.edu (original) (raw)
Papers by Shalley Sharma
Biomass Conversion and Biorefinery
Agricultural residues could become feedstocks for biobased products as they are renewable, carbon... more Agricultural residues could become feedstocks for biobased products as they are renewable, carbon neutral, and do not compete with food. In India, > 130 MT rice straw is available annually for alternate uses. Exploiting this abundant biomass for biochemical production will pave way for bio-based economy. Rice straw is highly recalcitrant due to lignin-carbohydrate complex and high ash. For production of value added products, the cellulose fraction is very important and also lignin can be used. However, for overall economic efficiency, it is imperative to separate and recover these fractions maximally from biomass and convert them into high value products at high titers and efficiency. Biomass has to be deconstructed to access these fractions. An improvised pretreatment with sodium hydroxide (NaOH) coupled with acidified water wash enabled high retrieval of cellulose and lignin. More than 80% of cellulose present in raw rice straw was recovered in pretreated solids and lignin (> 65%) recovered from acidification of alkali prehydrolysates/wash waters. Enzymatic hydrolysis of solids with commercial cellulases resulted in 80–100% glucan conversion at 6% and 3% loading respectively yielding ~ 5.5% and 3.3% sugar syrups which can be fermented to value added chemicals. Saccharomyces cerevisiae LN fermented hydrolysates with 77–97% efficiency producing 0.508 gg−1 and 0.403 gg−1ethanol within 24 h consuming all glucose while xylose was unutilized. Material calculations showed that this process converted 63% of cellulose present in rice straw to ethanol potentially yielding 135 L ethanol and ~ 100 Kg lignin per ton of rice straw with limited water use.
Applied Biochemistry and Biotechnology, 2021
The original version of this article unfortunately contained a mistake in the article title. The ... more The original version of this article unfortunately contained a mistake in the article title. The correct data are shown here. "Protoplasst" should read as "Protoplast." The original article has been corrected. Publisher's Note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Applied Biochemistry and Biotechnology, 2021
Co-utilization of xylose and glucose and subsequent fermentation using Saccharomyces cerevisiae c... more Co-utilization of xylose and glucose and subsequent fermentation using Saccharomyces cerevisiae could enhance ethanol productivity. Directed engineering approaches have met with limited success due to interconnectivity of xylose metabolism with other intrinsic, hidden pathways. Therefore, random approaches like protoplast fusion were used to reprogram unidentified mechanisms. Saccharomyces cerevisiae LN, the best hexose fermenter, was fused with xylose fermenting Pichia stipitis NCIM 3498. Protoplasts prepared using glucanex were fused under electric impulse and fusants were selected using 10% ethanol and cycloheximide (50 ppm) markers. Two fusants, 1a.23 and 1a.30 showing fast growth on xylose and tolerance to 10% ethanol, were selected. Higher extracellular protein expression observed in fusants as compared to parents was corroborated by higher number of bands resolved by twodimensional analysis. Overexpression of XYL1, XYL2, XKS and XUT4 in fusants as compared to S. cerevisiae LN as observed by RT-PCR analysis was substantiated by higher specific activities of XR, XDH and XKS enzymes in fusants. During lignocellulosic hydrolysate fermentation, fusants could utilize glucose faster than the parent P. stipitis NCIM 3498 and xylose consumption in fusants was higher than S. cerevisiae LN.
Annals of Microbiology, 2020
Purpose Efficient ethanol production through lignocellulosic biomass hydrolysates could solve ene... more Purpose Efficient ethanol production through lignocellulosic biomass hydrolysates could solve energy crisis as it is economically sustainable and ecofriendly. Saccharomyces cerevisiae is the work horse for lignocellulosic bioethanol production at industrial level. But its inability to ferment and utilize xylose limits the overall efficacy of the process. Method Data for the review was selected using different sources, such as Biofuels digest, Statista, International energy agency (IEA). Google scholar was used as a search engine to search literature for yeast metabolic engineering approaches. Keywords used were metabolic engineering of yeast for bioethanol production from lignocellulosic biomass. Result Through these approaches, interconnected pathways can be targeted randomly. Moreover, the improved strains genetic makeup can help us understand the mechanisms involved for this purpose. Conclusion This review discusses all possible approaches for metabolic engineering of yeast. Thes...
Renewable Energy, 2019
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Waste and Biomass Valorization, 2018
Rice straw, an abundant agro-residue, is available for energy production. In many parts of Asian ... more Rice straw, an abundant agro-residue, is available for energy production. In many parts of Asian countries, it is burnt on fields causing harm to the environment. Rice straw contains lignin, cellulose, hemicelluloses, and silicates making it recalcitrant. Pretreatment processes disintegrate lignin-carbohydrate matrix for efficient bioconversion of polysaccharides to fermentable sugars. A good number of physical, biological and chemical processes have been tried but degradation of polysaccharides and subsequent fermentation is still a challenge. Alkaline pretreatment causes effective delignification and swelling of biomass. The present study was performed on alkaline pretreatment of rice straw with 1% NaOH by autoclaving for 30 min at 121 °C at 10% solid loading. It was extracted with water to remove lignins, solids separated by filtrations and washed again to neutralize the pH. Water washing also led to removal of phenolic inhibitors. High (63%) glucan enrichment was obtained with concomitant lignin loss. Dry matter loss was around 50%. Enzymatic saccharification of the pretreated solids at 5 and 10% with Accellerase® 1500 for 24 h at 50 °C gave saccharification efficiency 76 and ~ 50% respectively. Hydrolysates containing 18 and 23 gL −1 sugars, supplemented with minimal salts, yeast extract, fermented by S. cerevisiae LN for 24 h yielded ~ 2 and 4 gL −1 ethanol with fermentation efficiency 55-66%. Thus, NaOH pretreatment is a cost effective option for ethanol production from rice straw. Lignin removed in prehydrolysates can be recovered by acidification.
Frontiers in Bioengineering and Biotechnology, 2018
* SEm denotes Standard error of mean; * * CD@5% denotes critical difference @ 5%.
Frontiers in Bioengineering and Biotechnology, 2018
Economics of ethanol production from lignocellulosic biomass depends on complete utilization of c... more Economics of ethanol production from lignocellulosic biomass depends on complete utilization of constituent carbohydrates and efficient fermentation of mixed sugars present in biomass hydrolysates. Saccharomyces cerevisiae, the commercial strain for ethanol production uses only glucose while pentoses remain unused. Recombinant strains capable of utilizing pentoses have been engineered but with limited success. Recently, presence of endogenous pentose assimilation pathway in S. cerevisiae was reported. On the contrary, evolutionary engineering of native xylose assimilating strains is promising approach. In this study, a native strain S. cerevisiae LN, isolated from fruit juice, was found to be capable of xylose assimilation and mixed sugar fermentation. Upon supplementation with yeast extract and peptone, glucose (10%) fermentation efficiency was 78% with ∼90% sugar consumption. Medium engineering augmented mixed sugars (5% glucose + 5% xylose) fermentation efficiency to ∼50 and 1.6% ethanol yield was obtained with concomitant sugar consumption ∼60%. Statistical optimization of input variables Glucose (5.36%), Xylose (3.30%), YE (0.36%), and peptone (0.25%) with Response surface methodology led to improved sugar consumption (74.33%) and 2.36% ethanol within 84 h. Specific activities of Xylose Reductase and Xylitol Dehydrogenase exhibited by S. cerevisiae LN were relatively low. Their ratio indicated metabolism diverted toward ethanol than xylitol and other byproducts. Strain was tolerant to concentrations of HMF, furfural and acetic acid commonly encountered in biomass hydrolysates. Thus, genetic setup for xylose assimilation in S. cerevisiae LN is not merely artifact of xylose metabolizing pathway and can be augmented by adaptive evolution. This strain showed potential for commercial exploitation.
Biofuel and Biorefinery Technologies, 2016
Lignocellulosic biomass is currently the most promising alternative energy source for realizing s... more Lignocellulosic biomass is currently the most promising alternative energy source for realizing sustainable demands of agrarian economies. Its natural recalcitrance to degradation necessitates a detailed study on the complex biochemistry involved in bioconversion of this lignin–carbohydrate complex. A comprehension of the enzymology and role of principal and accessory glycosyl hydrolases involved in biomass degradation are, hence, noteworthy in this context and the xyloglucan-active hydrolases warrant special mention. These are enzymes which carry out hydrolysis and transglucosylation of xyloglucan, the major hemicellulosic polysaccharide in plant biomass. The structurally complex xyloglucans cover and cross-link the cellulosic microfibrils in plant cell walls and make cellulose inaccessible to saccharification by cellulases. Solubilisation of biomass polysaccharides and release of sugars are central to the biomass-to-bioethanol process. Complete conversion of biomass carbohydrates requires a suite of hydrolytic enzymes, which may be designed specifically to accommodate the predominant and subsidiary biomass-cleaving enzymes. Xyloglucan hydrolases which are known to act synergistically with cellulases and xylanases in loosening the plant cell wall are vital enzymes to be deployed for successful bioconversion processes. This chapter is an insight into the capacity of these accessory, but indispensable, hydrolytic enzymes in unlocking the inaccessible biomass polysaccharides for increased sugar recovery and thereby, in drafting the fuels of future.
Biocatalysis and Agricultural Biotechnology, 2016
Bioethanol has been recognized as a promising contemporary fuel. One of the most abundant renewab... more Bioethanol has been recognized as a promising contemporary fuel. One of the most abundant renewable resources for bioethanol production is paddy straw with high carbohydrate content. A pretreatment step disintegrates the recalcitrant lignocellulosic structure in biomass, which facilitates the access of hydrolytic enzymes to the glucan macrostructure. Biological pretreatment is an eco-friendly alternative to harsh thermo-chemical pretreatment methodologies. In this study, paddy straw (rice variety Pusa 2511) was subjected to biological pretreatment with whiterot fungus, Trametes hirsuta and simultaneously with steam pretreatment at 121 °C. Resultant saccharification efficiencies of differentially pretreated paddy straw were compared to evaluate biological pretreatment. After pretreatment cellulose content in steam treated paddy straw was 39.5%, whereas for biological it was 37.6% and respective lignin contents were 14.2% and 4.7%. Lignin removal was substantially higher in biological pretreatment than steam pretreatment. The saccharification yields of biological pretreatment were at par with steam pretreated paddy straw. Highest saccharification efficiency was observed after 24 h, at 2% glucan loading, for both 2 biological (76.5%) and steam pretreatment (74.1%). Maximum production of sugar (52.91 g L-1) was observed in biologically pretreated biomass 10% glucan loading after 24 h. Fermentation of biomass hydrolysates with Saccharomyces cerevisiae, showed low ethanol production from biologically (0.86 g L-1) as well as steam pretreated biomass (1.13 g L-1) with fermentation efficiency ranging from 26-52%, suggesting presence of inhibitory factors necessitating detoxification of hydrolysates. This study, established biological pretreatment as feasible method for pretreatment and higher sugar yields.
Springer Proceedings in Energy, 2016
Bioethanol, a second generation biofuel, is considered to be one of the best alternatives to conv... more Bioethanol, a second generation biofuel, is considered to be one of the best alternatives to conventional petroleum-based liquid fuels. In the present scenario, it is being majorly produced by fermentation of hexoses coming from the cellulosic fraction of the lignocellulosic biomass. Biomass also comprises of up to 33 % hemicellulose, therefore, its fermentation would lead to enhanced bioethanol fermentation productivities. Bioethanol can be produced through biochemical as well as thermochemical processes. A biochemical process, which is environmentally favorable involves the use of microbes, e.g., yeast and bacteria. Bioethanol production from yeast, i.e., Saccharomyces cerevisiae has already been commercialized. However, demerit of this commercially viable strain is that it utilizes only hexoses, while pentoses are left unused. This paper discusses different strategies for improving the potential of yeast strains for mixed sugar fermentation to ethanol. There are ways to genetically improve yeast strains to enable them to ferment mixture of hexoses and pentoses. However, there are several physiological hurdles which can limit the success of conventional genetic approaches like cofactor imbalance, excessive by product formation, glucose repression, etc., which need to be tackled, in order to obtain enhanced yield. Metabolic engineering of the yeast strains is a way for enhancing bioethanol fermentation efficiency.
BMC Microbiology, 2014
Background: Species of the genus Pediococcus are known to produce antimicrobial peptides such as ... more Background: Species of the genus Pediococcus are known to produce antimicrobial peptides such as pediocin-like bacteriocins that contain YGNGVXC as a conserved motif at their N-terminus. Until now, the molecular weight of various bacteriocins produced by different strains of the genus Pediococcus have been found to vary between 2.7 to 4.6 kD. In the present study, we characterized an antimicrobial peptide produced by P. pentosaceus strain IE-3. Results: Antimicrobial peptide was isolated and purified from the supernatant of P. pentosaceus strain IE-3 grown for 48 h using cation exchange chromatography and reversed-phase high-performance liquid chromatography (RP-HPLC) techniques. While MALDI-TOF MS experiments determined the precise molecular mass of the peptide to be 1701.00 Da, the de novo sequence (APVPFSCTRGCLTHLV) of the peptide revealed no similarity with reported pediocins and did not contain the YGNGVXC conserved motif. Unlike pediocin-like bacteriocins, the low molecular weight peptide (LMW) showed resistance to different proteases. Moreover, peptide treated with reducing agent like dithiothreitol (DTT) exhibited increased activity against both Gram-positive and Gram-negative test strains in comparison to native peptide. However, peptide treated with oxidizing agent such as hydrogen peroxide (H 2 O 2) did not show any antimicrobial activity. Conclusion: To our knowledge this is the lowest molecular weight peptide produced by members of the genus Pediococcus. The low molecular weight peptide shared amino acid arrangement with N-terminal sequence of Class IIa, pediocin-like bacteriocins and showed increased activity under reducing conditions. Antimicrobial peptides active under reduced conditions are valuable for the preservation of processed foods like meat, dairy and canned foods where low redox potential prevails.
FEBS Journal, 2014
The growing emergence of antibiotic-resistant bacteria has led to the exploration of naturally oc... more The growing emergence of antibiotic-resistant bacteria has led to the exploration of naturally occurring defense peptides as antimicrobials. In this study, we found that laterosporulin (LS), a class IId bacteriocin, effectively kills active and nonmultiplying cells of both Gram-positive and Gram-negative bacteria. Fluorescence and electron microscopy suggest that growth inhibition occurs because of increased membrane permeability. The crystal structure of LS at 2.0 Å resolution reveals an all-β conformation of this peptide, with four β-strands forming a twisted β-sheet. All six intrinsic cysteines are intramolecularly disulfide-bonded, with two disulfides constraining the N terminus of the peptide and the third disulfide crosslinking the extreme C terminus, resulting in the formation of a closed structure. The significance of disulfides in maintaining the in-solution peptide structure was confirmed by CD and fluorescence analyses. Despite a low overall sequence similarity, LS has disulfide connectivity [C(I)-C(V), C(II)-C(IV), and C(III)-C(VI)] like that of β-defensins and a striking architectural similarity with α-defensins. Therefore LS presents a missing link between bacteriocins and mammalian defensins, and is also a potential antimicrobial lead, in particular against nonmultiplying bacteria.
International Journal of Systematic and Evolutionary Microbiology, 2011
A novel, Gram-staining-negative, yellow-coloured, rod-shaped, obligately aerobic, non-motile bact... more A novel, Gram-staining-negative, yellow-coloured, rod-shaped, obligately aerobic, non-motile bacterium, designated strain AK7T, was isolated from seawater collected on the coast at Visakhapatnam, Andhra Pradesh, India. The predominant fatty acids of the novel strain were iso-C15 : 0, iso-C15 : 0 3-OH, C16 : 1ω5c, iso-C17 : 0 3-OH and summed features 3 (C16 : 1ω7c and/or iso-C15 : 0 2-OH) and 4 (iso-C17 : 1 I and/or anteiso-C17 : 1 B). The major respiratory quinone was MK-7 and the polar lipid profile comprised phosphatidylethanolamine, two unidentified aminolipids and four other unidentified lipids. In phylogenetic analysis based on 16S rRNA gene sequences, strain AK7T appeared most closely related to Fulvivirga kasyanovii KMM 6220T (95.9 % sequence similarity), a member of the family Flammeovirgaceae in the phylum Bacteroidetes . The genomic DNA G+C content of strain AK7T was 55.1 mol%. Based on the morphological, biochemical, physiological, chemotaxonomic and phylogenetic evidence...
BMC Microbiology, 2013
Background Increasing multidrug-resistance in bacteria resulted in a greater need to find alterna... more Background Increasing multidrug-resistance in bacteria resulted in a greater need to find alternative antimicrobial substances that can be used for clinical applications or preservation of food and dairy products. Research on antimicrobial peptides including lipopeptides exhibiting both narrow and broad spectrum inhibition activities is increasing in the recent past. Therefore, the present study was aimed at isolation and characterization of antimicrobial lipopeptide producing bacterial strains from fecal contaminated soil sample. Results The phenotypic and 16S rRNA gene sequence analysis of all isolates identified them as different species of Gram-negative genera Citrobacter and Enterobacter. They exhibited common phenotypic traits like citrate utilization, oxidase negative and facultative anaerobic growth. The HPLC analysis of solvent extracts obtained from cell free fermented broth revealed the presence of multiple antimicrobial lipopeptides. The comprehensive mass spectral analy...
Antonie van Leeuwenhoek, 2012
The GenBank/EMBL/DDBJ accession number for the 16S rRNA gene sequence of strain AK2 T is FN994992... more The GenBank/EMBL/DDBJ accession number for the 16S rRNA gene sequence of strain AK2 T is FN994992. A Gram-negative, rod shaped, motile bacterium, was isolated from a marine solar saltern sample collected from Kakinada, India. Strain AK2 T was positive for nitrate reduction, catalase, Ala-Phe-Proarylamidase, β-galactosidase, β-N-acetylglucosaminidase, β-glucosidase, β-xylosidase, α-glucosidase, α-galactosidase and phosphatase activities, hydrolysis of aesculin, Tween 20/40/60/80 and urea. It was negative for oxidase, lysine decarboxylase and ornithine decarboxylase activities and could not hydrolyze agar, casein, gelatin and starch. The predominant fatty acids were iso-C 15:0 (28.2%), anteiso-C 15:0 (23.2%), iso-C 13:0 (19.9%) and iso-C 15:0 3-OH (13.9%). Strain AK2 T contained menaquinone with seven isoprene units (MK-7) as the sole respiratory quinone and phosphatidylethanolamine, one unidentified phospholipid and three unidentified lipids as polar lipids. The 16S rRNA gene sequence analysis indicated the strain AK2 T as a member of the genus Marinilabilia and closely related to Marinilabilia salmonicolor with pair-wise sequence similarity of 98.2%. Phylogenetic analysis of 16S rRNA gene revealed that the strain AK2 T clustered with Marinilabilia salmonicolor. However, DNA-DNA hybridization with Marinilabilia salmonicolor JCM 21150 T showed a relatedness of 48% with respect to strain AK2 T. The DNA G + C content of the strain was 40.2 mol%. Based on the phenotypic characteristics and phylogenetic inference, it is confirmed that the strain AK2 T represents a novel species of the genus Marinilabilia, for which the name Marinilabilia nitratireducens sp. nov. is proposed. The type strain of Marinilabilia nitratireducens sp. nov. is AK2 T (= MTCC 11402 T = JCM 17679 T).
Chemistry Central journal, Jan 5, 2018
Bioethanol obtained by fermenting cellulosic fraction of biomass holds promise for blending in pe... more Bioethanol obtained by fermenting cellulosic fraction of biomass holds promise for blending in petroleum. Cellulose hydrolysis yields glucose while hemicellulose hydrolysis predominantly yields xylose. Economic feasibility of bioethanol depends on complete utilization of biomass carbohydrates and an efficient co-fermenting organism is a prerequisite. While hexose fermentation capability of Saccharomyces cerevisiae is a boon, however, its inability to ferment pentose is a setback. Two xylose fermenting Kodamaea ohmeri strains were isolated from Lagenaria siceraria flowers through enrichment on xylose. They showed 61% glucose fermentation efficiency in fortified medium. Medium engineering with 0.1% yeast extract and peptone, stimulated co-fermentation potential of both strains yielding maximum ethanol 0.25 g gon mixed sugars with ~ 50% fermentation efficiency. Strains were tolerant to inhibitors like 5-hydroxymethyl furfural, furfural and acetic acid. Both K. ohmeri strains grew well ...
Additional file 1. Table S1. Sugar utilization by K. ohmeri strain 5 and strain 6. Table S2. Etha... more Additional file 1. Table S1. Sugar utilization by K. ohmeri strain 5 and strain 6. Table S2. Ethanol production, sugar consumption and fermentation efficiency of K. ohmeri strain 5 and strain 6 during xylose fermentation. Figure S1. Growth of K. ohmeri strain 5 and strain 6 on minimal medium with xylose as sole C source. Figure S2. K. ohmeri strain 5 (A) and strain 6 (B) as observed under phase contrast microscope. Figure S3. Effect of furfural on K. ohmeri strain 5 (A) and strain 6 (B).
Biomass Conversion and Biorefinery
Agricultural residues could become feedstocks for biobased products as they are renewable, carbon... more Agricultural residues could become feedstocks for biobased products as they are renewable, carbon neutral, and do not compete with food. In India, > 130 MT rice straw is available annually for alternate uses. Exploiting this abundant biomass for biochemical production will pave way for bio-based economy. Rice straw is highly recalcitrant due to lignin-carbohydrate complex and high ash. For production of value added products, the cellulose fraction is very important and also lignin can be used. However, for overall economic efficiency, it is imperative to separate and recover these fractions maximally from biomass and convert them into high value products at high titers and efficiency. Biomass has to be deconstructed to access these fractions. An improvised pretreatment with sodium hydroxide (NaOH) coupled with acidified water wash enabled high retrieval of cellulose and lignin. More than 80% of cellulose present in raw rice straw was recovered in pretreated solids and lignin (> 65%) recovered from acidification of alkali prehydrolysates/wash waters. Enzymatic hydrolysis of solids with commercial cellulases resulted in 80–100% glucan conversion at 6% and 3% loading respectively yielding ~ 5.5% and 3.3% sugar syrups which can be fermented to value added chemicals. Saccharomyces cerevisiae LN fermented hydrolysates with 77–97% efficiency producing 0.508 gg−1 and 0.403 gg−1ethanol within 24 h consuming all glucose while xylose was unutilized. Material calculations showed that this process converted 63% of cellulose present in rice straw to ethanol potentially yielding 135 L ethanol and ~ 100 Kg lignin per ton of rice straw with limited water use.
Applied Biochemistry and Biotechnology, 2021
The original version of this article unfortunately contained a mistake in the article title. The ... more The original version of this article unfortunately contained a mistake in the article title. The correct data are shown here. "Protoplasst" should read as "Protoplast." The original article has been corrected. Publisher's Note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Applied Biochemistry and Biotechnology, 2021
Co-utilization of xylose and glucose and subsequent fermentation using Saccharomyces cerevisiae c... more Co-utilization of xylose and glucose and subsequent fermentation using Saccharomyces cerevisiae could enhance ethanol productivity. Directed engineering approaches have met with limited success due to interconnectivity of xylose metabolism with other intrinsic, hidden pathways. Therefore, random approaches like protoplast fusion were used to reprogram unidentified mechanisms. Saccharomyces cerevisiae LN, the best hexose fermenter, was fused with xylose fermenting Pichia stipitis NCIM 3498. Protoplasts prepared using glucanex were fused under electric impulse and fusants were selected using 10% ethanol and cycloheximide (50 ppm) markers. Two fusants, 1a.23 and 1a.30 showing fast growth on xylose and tolerance to 10% ethanol, were selected. Higher extracellular protein expression observed in fusants as compared to parents was corroborated by higher number of bands resolved by twodimensional analysis. Overexpression of XYL1, XYL2, XKS and XUT4 in fusants as compared to S. cerevisiae LN as observed by RT-PCR analysis was substantiated by higher specific activities of XR, XDH and XKS enzymes in fusants. During lignocellulosic hydrolysate fermentation, fusants could utilize glucose faster than the parent P. stipitis NCIM 3498 and xylose consumption in fusants was higher than S. cerevisiae LN.
Annals of Microbiology, 2020
Purpose Efficient ethanol production through lignocellulosic biomass hydrolysates could solve ene... more Purpose Efficient ethanol production through lignocellulosic biomass hydrolysates could solve energy crisis as it is economically sustainable and ecofriendly. Saccharomyces cerevisiae is the work horse for lignocellulosic bioethanol production at industrial level. But its inability to ferment and utilize xylose limits the overall efficacy of the process. Method Data for the review was selected using different sources, such as Biofuels digest, Statista, International energy agency (IEA). Google scholar was used as a search engine to search literature for yeast metabolic engineering approaches. Keywords used were metabolic engineering of yeast for bioethanol production from lignocellulosic biomass. Result Through these approaches, interconnected pathways can be targeted randomly. Moreover, the improved strains genetic makeup can help us understand the mechanisms involved for this purpose. Conclusion This review discusses all possible approaches for metabolic engineering of yeast. Thes...
Renewable Energy, 2019
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Waste and Biomass Valorization, 2018
Rice straw, an abundant agro-residue, is available for energy production. In many parts of Asian ... more Rice straw, an abundant agro-residue, is available for energy production. In many parts of Asian countries, it is burnt on fields causing harm to the environment. Rice straw contains lignin, cellulose, hemicelluloses, and silicates making it recalcitrant. Pretreatment processes disintegrate lignin-carbohydrate matrix for efficient bioconversion of polysaccharides to fermentable sugars. A good number of physical, biological and chemical processes have been tried but degradation of polysaccharides and subsequent fermentation is still a challenge. Alkaline pretreatment causes effective delignification and swelling of biomass. The present study was performed on alkaline pretreatment of rice straw with 1% NaOH by autoclaving for 30 min at 121 °C at 10% solid loading. It was extracted with water to remove lignins, solids separated by filtrations and washed again to neutralize the pH. Water washing also led to removal of phenolic inhibitors. High (63%) glucan enrichment was obtained with concomitant lignin loss. Dry matter loss was around 50%. Enzymatic saccharification of the pretreated solids at 5 and 10% with Accellerase® 1500 for 24 h at 50 °C gave saccharification efficiency 76 and ~ 50% respectively. Hydrolysates containing 18 and 23 gL −1 sugars, supplemented with minimal salts, yeast extract, fermented by S. cerevisiae LN for 24 h yielded ~ 2 and 4 gL −1 ethanol with fermentation efficiency 55-66%. Thus, NaOH pretreatment is a cost effective option for ethanol production from rice straw. Lignin removed in prehydrolysates can be recovered by acidification.
Frontiers in Bioengineering and Biotechnology, 2018
* SEm denotes Standard error of mean; * * CD@5% denotes critical difference @ 5%.
Frontiers in Bioengineering and Biotechnology, 2018
Economics of ethanol production from lignocellulosic biomass depends on complete utilization of c... more Economics of ethanol production from lignocellulosic biomass depends on complete utilization of constituent carbohydrates and efficient fermentation of mixed sugars present in biomass hydrolysates. Saccharomyces cerevisiae, the commercial strain for ethanol production uses only glucose while pentoses remain unused. Recombinant strains capable of utilizing pentoses have been engineered but with limited success. Recently, presence of endogenous pentose assimilation pathway in S. cerevisiae was reported. On the contrary, evolutionary engineering of native xylose assimilating strains is promising approach. In this study, a native strain S. cerevisiae LN, isolated from fruit juice, was found to be capable of xylose assimilation and mixed sugar fermentation. Upon supplementation with yeast extract and peptone, glucose (10%) fermentation efficiency was 78% with ∼90% sugar consumption. Medium engineering augmented mixed sugars (5% glucose + 5% xylose) fermentation efficiency to ∼50 and 1.6% ethanol yield was obtained with concomitant sugar consumption ∼60%. Statistical optimization of input variables Glucose (5.36%), Xylose (3.30%), YE (0.36%), and peptone (0.25%) with Response surface methodology led to improved sugar consumption (74.33%) and 2.36% ethanol within 84 h. Specific activities of Xylose Reductase and Xylitol Dehydrogenase exhibited by S. cerevisiae LN were relatively low. Their ratio indicated metabolism diverted toward ethanol than xylitol and other byproducts. Strain was tolerant to concentrations of HMF, furfural and acetic acid commonly encountered in biomass hydrolysates. Thus, genetic setup for xylose assimilation in S. cerevisiae LN is not merely artifact of xylose metabolizing pathway and can be augmented by adaptive evolution. This strain showed potential for commercial exploitation.
Biofuel and Biorefinery Technologies, 2016
Lignocellulosic biomass is currently the most promising alternative energy source for realizing s... more Lignocellulosic biomass is currently the most promising alternative energy source for realizing sustainable demands of agrarian economies. Its natural recalcitrance to degradation necessitates a detailed study on the complex biochemistry involved in bioconversion of this lignin–carbohydrate complex. A comprehension of the enzymology and role of principal and accessory glycosyl hydrolases involved in biomass degradation are, hence, noteworthy in this context and the xyloglucan-active hydrolases warrant special mention. These are enzymes which carry out hydrolysis and transglucosylation of xyloglucan, the major hemicellulosic polysaccharide in plant biomass. The structurally complex xyloglucans cover and cross-link the cellulosic microfibrils in plant cell walls and make cellulose inaccessible to saccharification by cellulases. Solubilisation of biomass polysaccharides and release of sugars are central to the biomass-to-bioethanol process. Complete conversion of biomass carbohydrates requires a suite of hydrolytic enzymes, which may be designed specifically to accommodate the predominant and subsidiary biomass-cleaving enzymes. Xyloglucan hydrolases which are known to act synergistically with cellulases and xylanases in loosening the plant cell wall are vital enzymes to be deployed for successful bioconversion processes. This chapter is an insight into the capacity of these accessory, but indispensable, hydrolytic enzymes in unlocking the inaccessible biomass polysaccharides for increased sugar recovery and thereby, in drafting the fuels of future.
Biocatalysis and Agricultural Biotechnology, 2016
Bioethanol has been recognized as a promising contemporary fuel. One of the most abundant renewab... more Bioethanol has been recognized as a promising contemporary fuel. One of the most abundant renewable resources for bioethanol production is paddy straw with high carbohydrate content. A pretreatment step disintegrates the recalcitrant lignocellulosic structure in biomass, which facilitates the access of hydrolytic enzymes to the glucan macrostructure. Biological pretreatment is an eco-friendly alternative to harsh thermo-chemical pretreatment methodologies. In this study, paddy straw (rice variety Pusa 2511) was subjected to biological pretreatment with whiterot fungus, Trametes hirsuta and simultaneously with steam pretreatment at 121 °C. Resultant saccharification efficiencies of differentially pretreated paddy straw were compared to evaluate biological pretreatment. After pretreatment cellulose content in steam treated paddy straw was 39.5%, whereas for biological it was 37.6% and respective lignin contents were 14.2% and 4.7%. Lignin removal was substantially higher in biological pretreatment than steam pretreatment. The saccharification yields of biological pretreatment were at par with steam pretreated paddy straw. Highest saccharification efficiency was observed after 24 h, at 2% glucan loading, for both 2 biological (76.5%) and steam pretreatment (74.1%). Maximum production of sugar (52.91 g L-1) was observed in biologically pretreated biomass 10% glucan loading after 24 h. Fermentation of biomass hydrolysates with Saccharomyces cerevisiae, showed low ethanol production from biologically (0.86 g L-1) as well as steam pretreated biomass (1.13 g L-1) with fermentation efficiency ranging from 26-52%, suggesting presence of inhibitory factors necessitating detoxification of hydrolysates. This study, established biological pretreatment as feasible method for pretreatment and higher sugar yields.
Springer Proceedings in Energy, 2016
Bioethanol, a second generation biofuel, is considered to be one of the best alternatives to conv... more Bioethanol, a second generation biofuel, is considered to be one of the best alternatives to conventional petroleum-based liquid fuels. In the present scenario, it is being majorly produced by fermentation of hexoses coming from the cellulosic fraction of the lignocellulosic biomass. Biomass also comprises of up to 33 % hemicellulose, therefore, its fermentation would lead to enhanced bioethanol fermentation productivities. Bioethanol can be produced through biochemical as well as thermochemical processes. A biochemical process, which is environmentally favorable involves the use of microbes, e.g., yeast and bacteria. Bioethanol production from yeast, i.e., Saccharomyces cerevisiae has already been commercialized. However, demerit of this commercially viable strain is that it utilizes only hexoses, while pentoses are left unused. This paper discusses different strategies for improving the potential of yeast strains for mixed sugar fermentation to ethanol. There are ways to genetically improve yeast strains to enable them to ferment mixture of hexoses and pentoses. However, there are several physiological hurdles which can limit the success of conventional genetic approaches like cofactor imbalance, excessive by product formation, glucose repression, etc., which need to be tackled, in order to obtain enhanced yield. Metabolic engineering of the yeast strains is a way for enhancing bioethanol fermentation efficiency.
BMC Microbiology, 2014
Background: Species of the genus Pediococcus are known to produce antimicrobial peptides such as ... more Background: Species of the genus Pediococcus are known to produce antimicrobial peptides such as pediocin-like bacteriocins that contain YGNGVXC as a conserved motif at their N-terminus. Until now, the molecular weight of various bacteriocins produced by different strains of the genus Pediococcus have been found to vary between 2.7 to 4.6 kD. In the present study, we characterized an antimicrobial peptide produced by P. pentosaceus strain IE-3. Results: Antimicrobial peptide was isolated and purified from the supernatant of P. pentosaceus strain IE-3 grown for 48 h using cation exchange chromatography and reversed-phase high-performance liquid chromatography (RP-HPLC) techniques. While MALDI-TOF MS experiments determined the precise molecular mass of the peptide to be 1701.00 Da, the de novo sequence (APVPFSCTRGCLTHLV) of the peptide revealed no similarity with reported pediocins and did not contain the YGNGVXC conserved motif. Unlike pediocin-like bacteriocins, the low molecular weight peptide (LMW) showed resistance to different proteases. Moreover, peptide treated with reducing agent like dithiothreitol (DTT) exhibited increased activity against both Gram-positive and Gram-negative test strains in comparison to native peptide. However, peptide treated with oxidizing agent such as hydrogen peroxide (H 2 O 2) did not show any antimicrobial activity. Conclusion: To our knowledge this is the lowest molecular weight peptide produced by members of the genus Pediococcus. The low molecular weight peptide shared amino acid arrangement with N-terminal sequence of Class IIa, pediocin-like bacteriocins and showed increased activity under reducing conditions. Antimicrobial peptides active under reduced conditions are valuable for the preservation of processed foods like meat, dairy and canned foods where low redox potential prevails.
FEBS Journal, 2014
The growing emergence of antibiotic-resistant bacteria has led to the exploration of naturally oc... more The growing emergence of antibiotic-resistant bacteria has led to the exploration of naturally occurring defense peptides as antimicrobials. In this study, we found that laterosporulin (LS), a class IId bacteriocin, effectively kills active and nonmultiplying cells of both Gram-positive and Gram-negative bacteria. Fluorescence and electron microscopy suggest that growth inhibition occurs because of increased membrane permeability. The crystal structure of LS at 2.0 Å resolution reveals an all-β conformation of this peptide, with four β-strands forming a twisted β-sheet. All six intrinsic cysteines are intramolecularly disulfide-bonded, with two disulfides constraining the N terminus of the peptide and the third disulfide crosslinking the extreme C terminus, resulting in the formation of a closed structure. The significance of disulfides in maintaining the in-solution peptide structure was confirmed by CD and fluorescence analyses. Despite a low overall sequence similarity, LS has disulfide connectivity [C(I)-C(V), C(II)-C(IV), and C(III)-C(VI)] like that of β-defensins and a striking architectural similarity with α-defensins. Therefore LS presents a missing link between bacteriocins and mammalian defensins, and is also a potential antimicrobial lead, in particular against nonmultiplying bacteria.
International Journal of Systematic and Evolutionary Microbiology, 2011
A novel, Gram-staining-negative, yellow-coloured, rod-shaped, obligately aerobic, non-motile bact... more A novel, Gram-staining-negative, yellow-coloured, rod-shaped, obligately aerobic, non-motile bacterium, designated strain AK7T, was isolated from seawater collected on the coast at Visakhapatnam, Andhra Pradesh, India. The predominant fatty acids of the novel strain were iso-C15 : 0, iso-C15 : 0 3-OH, C16 : 1ω5c, iso-C17 : 0 3-OH and summed features 3 (C16 : 1ω7c and/or iso-C15 : 0 2-OH) and 4 (iso-C17 : 1 I and/or anteiso-C17 : 1 B). The major respiratory quinone was MK-7 and the polar lipid profile comprised phosphatidylethanolamine, two unidentified aminolipids and four other unidentified lipids. In phylogenetic analysis based on 16S rRNA gene sequences, strain AK7T appeared most closely related to Fulvivirga kasyanovii KMM 6220T (95.9 % sequence similarity), a member of the family Flammeovirgaceae in the phylum Bacteroidetes . The genomic DNA G+C content of strain AK7T was 55.1 mol%. Based on the morphological, biochemical, physiological, chemotaxonomic and phylogenetic evidence...
BMC Microbiology, 2013
Background Increasing multidrug-resistance in bacteria resulted in a greater need to find alterna... more Background Increasing multidrug-resistance in bacteria resulted in a greater need to find alternative antimicrobial substances that can be used for clinical applications or preservation of food and dairy products. Research on antimicrobial peptides including lipopeptides exhibiting both narrow and broad spectrum inhibition activities is increasing in the recent past. Therefore, the present study was aimed at isolation and characterization of antimicrobial lipopeptide producing bacterial strains from fecal contaminated soil sample. Results The phenotypic and 16S rRNA gene sequence analysis of all isolates identified them as different species of Gram-negative genera Citrobacter and Enterobacter. They exhibited common phenotypic traits like citrate utilization, oxidase negative and facultative anaerobic growth. The HPLC analysis of solvent extracts obtained from cell free fermented broth revealed the presence of multiple antimicrobial lipopeptides. The comprehensive mass spectral analy...
Antonie van Leeuwenhoek, 2012
The GenBank/EMBL/DDBJ accession number for the 16S rRNA gene sequence of strain AK2 T is FN994992... more The GenBank/EMBL/DDBJ accession number for the 16S rRNA gene sequence of strain AK2 T is FN994992. A Gram-negative, rod shaped, motile bacterium, was isolated from a marine solar saltern sample collected from Kakinada, India. Strain AK2 T was positive for nitrate reduction, catalase, Ala-Phe-Proarylamidase, β-galactosidase, β-N-acetylglucosaminidase, β-glucosidase, β-xylosidase, α-glucosidase, α-galactosidase and phosphatase activities, hydrolysis of aesculin, Tween 20/40/60/80 and urea. It was negative for oxidase, lysine decarboxylase and ornithine decarboxylase activities and could not hydrolyze agar, casein, gelatin and starch. The predominant fatty acids were iso-C 15:0 (28.2%), anteiso-C 15:0 (23.2%), iso-C 13:0 (19.9%) and iso-C 15:0 3-OH (13.9%). Strain AK2 T contained menaquinone with seven isoprene units (MK-7) as the sole respiratory quinone and phosphatidylethanolamine, one unidentified phospholipid and three unidentified lipids as polar lipids. The 16S rRNA gene sequence analysis indicated the strain AK2 T as a member of the genus Marinilabilia and closely related to Marinilabilia salmonicolor with pair-wise sequence similarity of 98.2%. Phylogenetic analysis of 16S rRNA gene revealed that the strain AK2 T clustered with Marinilabilia salmonicolor. However, DNA-DNA hybridization with Marinilabilia salmonicolor JCM 21150 T showed a relatedness of 48% with respect to strain AK2 T. The DNA G + C content of the strain was 40.2 mol%. Based on the phenotypic characteristics and phylogenetic inference, it is confirmed that the strain AK2 T represents a novel species of the genus Marinilabilia, for which the name Marinilabilia nitratireducens sp. nov. is proposed. The type strain of Marinilabilia nitratireducens sp. nov. is AK2 T (= MTCC 11402 T = JCM 17679 T).
Chemistry Central journal, Jan 5, 2018
Bioethanol obtained by fermenting cellulosic fraction of biomass holds promise for blending in pe... more Bioethanol obtained by fermenting cellulosic fraction of biomass holds promise for blending in petroleum. Cellulose hydrolysis yields glucose while hemicellulose hydrolysis predominantly yields xylose. Economic feasibility of bioethanol depends on complete utilization of biomass carbohydrates and an efficient co-fermenting organism is a prerequisite. While hexose fermentation capability of Saccharomyces cerevisiae is a boon, however, its inability to ferment pentose is a setback. Two xylose fermenting Kodamaea ohmeri strains were isolated from Lagenaria siceraria flowers through enrichment on xylose. They showed 61% glucose fermentation efficiency in fortified medium. Medium engineering with 0.1% yeast extract and peptone, stimulated co-fermentation potential of both strains yielding maximum ethanol 0.25 g gon mixed sugars with ~ 50% fermentation efficiency. Strains were tolerant to inhibitors like 5-hydroxymethyl furfural, furfural and acetic acid. Both K. ohmeri strains grew well ...
Additional file 1. Table S1. Sugar utilization by K. ohmeri strain 5 and strain 6. Table S2. Etha... more Additional file 1. Table S1. Sugar utilization by K. ohmeri strain 5 and strain 6. Table S2. Ethanol production, sugar consumption and fermentation efficiency of K. ohmeri strain 5 and strain 6 during xylose fermentation. Figure S1. Growth of K. ohmeri strain 5 and strain 6 on minimal medium with xylose as sole C source. Figure S2. K. ohmeri strain 5 (A) and strain 6 (B) as observed under phase contrast microscope. Figure S3. Effect of furfural on K. ohmeri strain 5 (A) and strain 6 (B).