Charlene Pillay - Academia.edu (original) (raw)

Papers by Charlene Pillay

biodegradation in contaminated soils

De Gruyter eBooks, Dec 7, 2020

Microbiologically Influenced Corrosion (MIC) is a process influenced by microbial presence and th... more Microbiologically Influenced Corrosion (MIC) is a process influenced by microbial presence and their metabolic activities. This study examined the microbial effects on metal corrosion under different environmental conditions with nutrient supplements. Experiments were conducted by inserting stainless steel 304 and mild steel coupons (2.5 x 2.5 cm 2) into loam soil and a simulated seawater/sediment system with various nutrient conditions (sterilized, without supplement, 5 mM NaNO 3 or NH 4 NO 3). Two mild and stainless steel coupons were removed monthly and the corrosion rate was evaluated based on the weight loss. Bacterial populations were enumerated using the most probable number (MPN) technique. The presence and adhesion of microbes on mild steel coupons were examined using Scanning Electron Microscopy (SEM). The extent of the corrosion process on the surface of the metal coupons were visualized by using the Stereo Microscope. The elemental composition of the corrosion products formed on the coupon surface were determined by Energy Dispersive X-Ray analyses. Isolation and identification of aerobic microorganisms were conducted and examined for its potential in either accelerating or inhibiting corrosion. The bacterial populations present on the mild steel surface were analyzed by fluorescent in situ hybridization. Denaturing gradient gel electrophoresis (DGGE) analyses of PCR-amplified 16S rDNA fragments were conducted to determine the microbial community complexity of the biofilm. Greater weight losses of mild steel in loam soil and the seawater/sediment system with NaNO 3 (48.86 mg/g and 19.96 mg/g of weight loss, respectively after 20 weeks) were observed with total heterotrophic bacterial population presented (106.695 MPN/ml and 0.11187 MPN/ml respectively) compared to the autoclaved control (7.17845 mg/g and 0.12082 mg/g of weight loss respectively). Supplementation of 5 mM NH 4 NO 3 increased the total heterotrophic bacterial population and resulted in a decrease in weight loss measurements on the stainless steel coupons (211.4 MPN/ml with a 0.01 mg/g weight loss) after 20 weeks compared to the non-autoclaved loam soil and loam soil supplemented with NaNO 3 (139.2 MPN/ml and 134.9 MPN/ml respectively with no weight loss). SEM images of the mild steel coupons confirmed the presence and adherence of bacteria on the metal surface. Stereo microscopic images displayed reddish-brown deposits and pitting on the coupon surface. Isolation, identification and sequence analysis revealed that most microorganisms were the Bacillus species. This group of microorganisms are iron-oxidizing bacteria that could also promote the corrosion process. After 20 weeks of incubation, the total SRB cell counts were lower in samples supplemented with NaNO 3 in both loam soil and the seawater/sediment system. This iii study also indicated that the isolated aerobic microorganisms do play a role in the corrosion process in both stainless and mild steel. DGGE analysis revealed microbial diversity in the corrosion products especially those affiliated to the bacterial phyla Firmicutes and Gamma-Proteobacteria. Fluorescent in situ hybridization analysis allowed for an overall estimation of Eubacteria and sulphate-reducing bacteria present in the biofilm formed on the surface of mild steel. The current study indicates that the addition of nitrates did not significantly reduce the rates of corrosion of both mild and stainless steel. However, it does seem that environmental conditions did pose as an important factor in the corrosion process. Therefore, further studies need to be implemented to analyze the environmental type, microbial composition and optimization of the concentration of nitrates for possible mitigation of metal corrosion. To optimize MIC prevention and control, collaboration between engineers and microbiologists proves advantageous to develop an environmentally sound and potentially cost-effective approach to control corrosion.

BENTHAM SCIENCE PUBLISHERS eBooks, Sep 14, 2022

Plants produce an array of secondary metabolites identified as possible antimicrobialagents that ... more Plants produce an array of secondary metabolites identified as possible antimicrobialagents that are used across the globe to treat numerous diseases and ailments.These secondary metabolites serve as unique commercial sources of variouspharmaceuticals, food additives and flavouring agents, and possess diverse industrialapplications. Alkaloids, flavonoids, and polyphenols are secondary metabolites shownto attack numerous gram-positive and gram negative bacteria in response to microbialinfections. Secondary plant metabolites have a detrimental effect on microbial cells inseveral ways, such as alteration of the structure and function of the cytoplasmicmembrane as well as DNA/RNA synthesis, interference with intermediary metabolism,interaction with membrane proteins, a disruption in the movement of protons leading toion leakage, enzyme synthesis inhibition, the clotting of cytoplasmic components andinterference in typical cell communication. This ultimately results in cell death. Thefocus of this chapter is to provide an overview of the function and benefits of plantsecondary metabolites as therapeutic agents to combat pathogenic bacterial infections.

International Biodeterioration & Biodegradation, Nov 25, 2013

Many microorganisms are reported to influence the corrosive behaviour of mild steel and stainless... more Many microorganisms are reported to influence the corrosive behaviour of mild steel and stainless steel in different habitats. In this study, 40 bacterial strains were isolated from corroded mild steel and stainless steel coupons in the nitrate supplemented environments. The corrosion abilities of the isolates against the mild steel and stainless steel coupons were tested with or without additional nitrate sources. The presence of bacterial isolates alone stimulated the corrosion of mild steel coupons. Most of the bio-corrosion processes of mild steel coupons were mitigated by adding nitrate supplement with bacterial isolates. The effects of bacterial isolates and additional nitrogen sources on corrosion of stainless steels were varied. Not all bacterial isolates stimulated the corrosion on stainless steel during the study period. Unlike the effects on mild steel coupons, additional NaNO3 might stimulate, retard the corrosion rate by the bacterial isolates or have limited effects. Similar results were obtained when NH4NO3 was used. Phylogenetic analysis demonstrated that all isolates were closely related. The majority of the bacterial isolates from corroded metal coupons were identified as Bacillus species. Others were identified as Pseudomonas sp., Marinobacter sp., and Halomonas species. The results prove that the isolated aerobic microorganisms do play a role in the corrosion process of stainless and mild steel. Adding additional nitrate sources might be a tool to mitigate corrosion of mild steel which was stimulated by the presence of bacteria. However, to prevent the corrosion of stainless steels, it might need a trial and errors approach in each case.

Metabolites

Recently, dipeptidyl peptidase-IV (DPP-IV) has become an effective target in the management of ty... more Recently, dipeptidyl peptidase-IV (DPP-IV) has become an effective target in the management of type-2 diabetes mellitus (T2D). The study aimed to determine the efficacy of shikimate pathway-derived phenolic acids as potential DPP-IV modulators in the management of T2D. The study explored in silico (molecular docking and dynamics simulations) and in vitro (DPP-IV inhibitory and kinetics assays) approaches. Molecular docking findings revealed chlorogenic acid (CA) among the examined 22 phenolic acids with the highest negative binding energy (−9.0 kcal/mol) showing a greater affinity for DPP-IV relative to the standard, Diprotin A (−6.6 kcal/mol). The result was corroborated by MD simulation where it had a higher affinity (−27.58 kcal/mol) forming a more stable complex with DPP-IV than Diprotin A (−12.68 kcal/mol). These findings were consistent with in vitro investigation where it uncompetitively inhibited DPP-IV having a lower IC50 (0.3 mg/mL) compared to Diprotin A (0.5 mg/mL). Whil...

Journal of Diabetes Research

Protein tyrosine phosphatase 1B (PTP1B), a negative regulator of the insulin signaling pathway, h... more Protein tyrosine phosphatase 1B (PTP1B), a negative regulator of the insulin signaling pathway, has gained attention as a validated druggable target in the management of type 2 diabetes mellitus (T2DM). The lack of clinically approved PTP1B inhibitors has continued to prompt research in plant-derived therapeutics possibly due to their relatively lesser toxicity profiles. Flavonoid C-glycosides are one of the plant-derived metabolites gaining increased relevance as antidiabetic agents, but their possible mechanism of action remains largely unknown. This study investigates the antidiabetic potential of flavonoid C-glycosides against PTP1B in silico and in vitro. Of the seven flavonoid C-glycosides docked against the enzyme, three compounds (apigenin, vitexin, and orientin) had the best affinity for the enzyme with a binding score of –7.3 kcal/mol each, relative to –7.4 kcal/mol for the reference standard, ursolic acid. A further probe (in terms of stability, flexibility, and compactne...

Journal of Animal Science and Biotechnology

The gastrointestinal tract (GIT) health impacts animal productivity. The poultry microbiome has f... more The gastrointestinal tract (GIT) health impacts animal productivity. The poultry microbiome has functions which range from protection against pathogens and nutrients production, to host immune system maturation. Fluctuations in the microbiome have also been linked to prevailing environmental conditions. Healthy poultry birds possess a natural resistance to infection. However, the exploration of environmental impacts and other relevant factors on poultry growth and health have been underplayed. Since good performance and growth rate are central to animal production, the host-microbiome relationship remains integral. Prior to the emergence of metagenomic techniques, conventional methods for poultry microbiome studies were used and were low-throughput and associated with insufficient genomic data and high cost of sequencing. Fortunately, the advent of high-throughput sequencing platforms have circumvented some of these shortfalls and paved the way for increased studies on the poultry g...

African Journal of Biotechnology

Uncontrolled releases of petroleum compounds that are carcinogenic, mutagenic and are potent immu... more Uncontrolled releases of petroleum compounds that are carcinogenic, mutagenic and are potent immunotoxicants into soil and groundwater poses a serious threat to human and animal health. Biodegradation of hydrocarbon-contaminated soils has been established as an efficient, economic, versatile and environmentally sound treatment. Ten indigenous microorganisms were isolated from contaminated soils using the enrichment technique. Five isolates with the highest degradation potentials under standard degradation conditions were identified as Acinetobacter calcoaceticus (LT 1 and ETS 2), Acinetobacter sp. (LT 1 A), Citrobacter freundii (MRC 3) and Bacillus pumilus (JL B). B. pumilus achieved 86.94% of diesel degradation in 2 weeks. Additional degradation assay was carried out in liquid media using 3 local commercial fertilizers as nutrient supplements in comparison with the Bushnell-Haas (BH) media. The results show that the addition of fertilizer F1 stimulated diesel degradation by all isolates especially B. pumilus while the addition of fertilizer F3 seemed to strongly inhibit the bacterial ability of diesel degradation. The inoculation with the consortia did not show a higher degradation potential than the individual isolate. The results strongly indicate that environmental conditions of the contaminated sites play a crucial role in the degradation even though additional diesel-degrader has been introduced into the contaminated site.

AFRICAN JOURNAL OF BIOTECHNOLOGY

The abilities of diesel-degrading Bacillus pumilus JL B and Acinetobacter calcoaceticus LT 1 were... more The abilities of diesel-degrading Bacillus pumilus JL B and Acinetobacter calcoaceticus LT 1 were tested in contaminated soils. The effect of nutrient supplementation on bioaugmented samples was also examined. The results show that bio-augmentation and biostimulation accelerated significantly (p < 0.05) the diesel degradation in the contaminated loam soil and sea sand. Supplementing fertilizers to the augmented loam samples did not result in a significantly higher degradation rate. Furthermore, A. calcoaceticus LT 1 alone failed to stimulate higher degradation rates in sea sand unless further supplementation of fertilizer. The results from environmental scanning electron microscopy demonstrate the population increases, then decreases in augmented samples corresponding to the level of diesel degradation. Fungi-like microorganisms became dominant in contaminated loam soil at the end of the study but not in sea sand. The study shows that it is critical not only to understand the phy...

African Journal of Biotechnology, 2009

Increasing public concern towards petroleum pollution demands for new and more environmentally ef... more Increasing public concern towards petroleum pollution demands for new and more environmentally efficient low-cost strategies for cleaning up contaminated sites. Diesel biodegradation by microbial communities was investigated in artificially contaminated soils by supplementing commercial fertilizers under laboratory conditions. The amounts of oil degraded at each sampling day were determined by the Soxhlet extraction method, the quantities of benzene, toluene, ethyl benzene, and xylene (BTEX) compounds and hydrocarbon content in the treated and non-treated soil samples were determined by gas chromatography-mass spectroscopy. The significant enhancement of diesel degradation was observed soon after the supplementation of fertilizers in loam soil and sea sand, but not in clay soil. The fertilizer supplements stimulated higher degradations, but no significant differences in contaminated sea sand and loam soil after 60 days of incubation period. The inhibitory effect of adding fertilizers was observed in the clay soil. The breakdown of hydrocarbon C> 16 were relatively faster than the shorter chain compounds such as C 9. In conclusion, the supplementation of fertilizer stimulates the diesel degradation rate in the contaminated soil and the effects of nutrient supplementation are dependant upon soil types, existing nutrients and microbial populations.

International Biodeterioration & Biodegradation, 2013

Corrosion Science, 2014

ABSTRACT This paper investigates the impact of additional nitrate sources on mild steel coupon co... more ABSTRACT This paper investigates the impact of additional nitrate sources on mild steel coupon corrosion in a seawater/sediment system. The results show that addition of 5 mM of nitrate sources significantly increased the weight loss of coupons after 20 weeks. SEM results indicate increase in microbial populations and corrosive products in the non-autoclaved and the nitrate-treated environments. EDX analyses revealed an increase in contents of carbon, calcium, magnesium, phosphorus and sodium with the exception of iron with an increase in incubation time.

International Biodeterioration & Biodegradation