Ammini Parvathi - Academia.edu (original) (raw)

Papers by Ammini Parvathi

Apple Academic Press eBooks, Dec 2, 2022

Diversity

Viral processes in the coastal and offshore regions of the Eastern Arabian Sea (west coast of Ind... more Viral processes in the coastal and offshore regions of the Eastern Arabian Sea (west coast of India) and their contribution of viral lysis to the organic carbon and nitrogen pool was examined. Water samples were collected during the southwest monsoon season at different depths (up to 1000 m) from four transects, with each transect consisting of two sampling points (S1–S8). Abundances of viruses and prokaryotes together with viral mediated prokaryotic mortality (up to 49.7%) were significantly (p < 0.001) higher in eutrophic coastal stations, whereas high percent lysogeny (up to 93%) was observed in the offshore regions. High viral-mediated carbon (Mean ± SD = 67.47 ± 2.0 μM C L−1 d−1) and nitrogen (Mean ± SD = 13.49 ± 14.0 μM N L−1 d−1) release was evident in the surface coastal waters compared to offshore regions. The percentage contributions of carbon and nitrogen released by viral lysis to the total dissolved organic carbon and nitrogen pool were estimated to be 7.4% and 3.9%,...

Environmental Science and Pollution Research, 2021

Archives of microbiology, 2021

Anthropogenic contamination of coastal-marine water is responsible for introducing multidrug-resi... more Anthropogenic contamination of coastal-marine water is responsible for introducing multidrug-resistant bacteria such as the pNDM-harbouring Escherichia coli into the seafood chain. This study was conducted to understand the survivability of a multidrug-resistant, the New Delhi Metallo-β-lactamase-producing E. coli (AS-EC121) in tropical seawater at room temperature (28-32 °C) compared to E. coli K12 strain. The experimental and control strains were inoculated at 6 log CFU/ml level into seawater. After an initial sharp decline in counts, AS-EC121 and K12 strains showed a gradual loss of viability after week-1 of inoculation. AS-EC121 was undetectable after day-56, while K12 colonies disappeared a week later, from day-63. The conjugation experiment revealed that pNDM was transferable to a recipient E. coli strain in seawater. This study suggests that the multidrug-resistant, pNDM-harbouring E. coli is able to survive in seawater for over 2 months stably maintaining the resistance plas...

Preparative Biochemistry & Biotechnology, 2019

Molecular Biology Reports, 2019

Microorganisms, 2022

Infectious diseases caused by bacterial species of the Vibrio genus have had considerable signifi... more Infectious diseases caused by bacterial species of the Vibrio genus have had considerable significance upon human health for centuries. V. cholerae is the causative microbial agent of cholera, a severe ailment characterized by profuse watery diarrhea, a condition associated with epidemics, and seven great historical pandemics. V. parahaemolyticus causes wound infection and watery diarrhea, while V. vulnificus can cause wound infections and septicemia. Species of the Vibrio genus with resistance to multiple antimicrobials have been a significant health concern for several decades. Mechanisms of antimicrobial resistance machinery in Vibrio spp. include biofilm formation, drug inactivation, target protection, antimicrobial permeability reduction, and active antimicrobial efflux. Integral membrane-bound active antimicrobial efflux pump systems include primary and secondary transporters, members of which belong to closely related protein superfamilies. The RND (resistance-nodulation-divi...

Regional Studies in Marine Science, 2020

Abstract Bacterial community structure was analysed from the coastal and offshore surface waters ... more Abstract Bacterial community structure was analysed from the coastal and offshore surface waters of the Bay of Bengal (BoB) using of Next Generation Sequencing (NGS) approach. Taxonomic richness was high in the offshore waters compared to the coastal waters. Analysis of sequence data revealed that both the offshore and coastal waters in our study were dominated by Proteobacteria (67.14% and 61.91%, respectively). The most dominant genera in the coastal waters were Synechococcus, Erythrobacter, Psychrobacter while Prochlorococcus, and Vibrio were dominant in the offshore waters. Interestingly, the distribution of minor phyla was distinctly different in coastal and offshore environments. Fusobacteria, Synergistetes, Fibrobacteres, Spirochaetes, Gemmatimonadetes, Chlorobi, Chlamydiae, and Armatimonadetes were the minor phyla (6.84%) present in offshore waters. The metabolic predictions of the bacterial communities revealed distinctly different activities in the coastal and offshore water samples, which could be attributed to the differences in the physico-chemical conditions and substrate availability. Major functions included sulfate reduction, oxalic acid degradation, dehalogenation, nitrite reduction, ammonia oxidation, nitrogen fixation, xylan degradation, and aromatic hydrocarbons degradation.

Antibiotics, 2021

Bacterial pathogens as causative agents of infection constitute an alarming concern in the public... more Bacterial pathogens as causative agents of infection constitute an alarming concern in the public health sector. In particular, bacteria with resistance to multiple antimicrobial agents can confound chemotherapeutic efficacy towards infectious diseases. Multidrug-resistant bacteria harbor various molecular and cellular mechanisms for antimicrobial resistance. These antimicrobial resistance mechanisms include active antimicrobial efflux, reduced drug entry into cells of pathogens, enzymatic metabolism of antimicrobial agents to inactive products, biofilm formation, altered drug targets, and protection of antimicrobial targets. These microbial systems represent suitable focuses for investigation to establish the means for their circumvention and to reestablish therapeutic effectiveness. This review briefly summarizes the various antimicrobial resistance mechanisms that are harbored within infectious bacteria.

Environmental Monitoring and Assessment, 2020

Marinobacter is an ecologically important genus of Gammaproteobacteria found in diverse marine ha... more Marinobacter is an ecologically important genus of Gammaproteobacteria found in diverse marine habitats, many species of which are capable of degrading hydrocarbons. In this study, we isolated a Marinobacter phage-host system from the surface waters of the Arabian Sea using enrichment culture methods, studied their growth characteristics and investigated the effect of salinity and nitrate concentrations on phage-host interactions. The bacterial isolate had maximum identity to Marinobacter salsuginis based on 16S rRNA similarities and was termed as Marinobacter sp., strain D1S9. It could tolerate up to 14% of NaCl with maximum growth at 11% NaCl. The host grew optimally between 35 and 40 °C and at pH 8. It had a generation time of 3.7 h with a mean growth rate of 0.27 h−1. The phage infected the host forming clear, round plaques of 1–2 mm diameter. It had a narrow host range restricted to the strain Marinobacter D1S9. The latent period and burst size of the phage were estimated to be 30 min and 106 phages per infected cell, respectively. The phage had an adsorption rate of 3.4 × 10−8 ml min−1 and retained 40.4% of its adsorption efficiency at 16% NaCl with a maximum at 4% NaCl (76.1%). Inorganic nitrate was found to have a direct role in controlling host growth and phage burst size.

Biotechnological Applications of Quorum Sensing Inhibitors, 2018

Bacterial pathogenesis is frequently enhanced by virulence mechanisms that facilitate growth. Suc... more Bacterial pathogenesis is frequently enhanced by virulence mechanisms that facilitate growth. Such virulence factors include biofilm formation and antimicrobial resistance mechanisms. One primary resistance mechanism involves the active efflux of antimicrobial agents from cells of pathogenic bacteria. It has been established that quorum sensing serves as a line of communication between the environment and mechanisms of antimicrobial resistance, such as antimicrobial efflux pump systems from bacterial pathogens. This chapter covers several well documented antimicrobial efflux transporter resistance mechanisms and their relationships to key aspects of quorum sensing. Knowledge of these critical relationships may enhance their biotechnological applications.

IET Nanobiotechnology, Sep 7, 2018

Aquatic Ecology

A conspicuous bioluminescence during nighttime was reported in an aquaculture farm in the Cochin ... more A conspicuous bioluminescence during nighttime was reported in an aquaculture farm in the Cochin estuary due to Gonyaulax spinifera bloom on March 20, 2020. In situ measurements on bioluminescence was carried out during nighttime to quantify the response of G. spinifera to various mechanical stimuli. The bioluminescence intensity (BI) was measured using Glowtracka, an advanced single channel sensor, attached to a Conductivity–Temperature–Depth Profiler. In steady environment, without any external stimuli, the bioluminescence generated due to the movement of fishes and shrimps in the water column was not detected by the sensor. However, stimuli such as a hand splash, oar and swimming movements, and a mixer could generate measurable bioluminescence responses. An abundance of ~ 2.7 × 106 cells L−1 of G. spinifera with exceptionally high chlorophyll a of 25 mg m−3 was recorded. The BI in response to hand splash was recorded as high as 1.6 × 1011 photons cm−2 s−1. Similarly, BI of ~ 1–6 × 1010 photons cm−2 s−1 with a cumulative bioluminescence of ~ 2.51 × 1012 photons cm−2 (for 35 s) was recorded when there is a mixer with a constant force of 494 N/800 rpm min−1. The response of G. spinifera was spontaneous with no time lapse between application of stimuli and the bioluminescence response. Interestingly, in natural environment, application of stimulus for longer time periods (10 min) does not lower the bioluminescence intensity due to the replenishment of water thrusted in by the mixer from surrounding areas. We also demonstrated that the bioluminescence intensity decreases with increase in distance from the source of stimuli (mixer) (av. 1.84 × 1010 photons cm−2 s−1 at 0.2 m to av. 0.05 × 1010 photons cm−2 s−1 at 1 m). The BI was highest in the periphery of the turbulent wake generated by the stimuli (av. 3.1 × 1010 photons cm−2 s−1) compared to the center (av. 1.8 × 1010 photons cm−2 s−1). When the stimuli was applied vertically down, the BI decreased from 0.2 m (0.3 × 1010 photons cm−2 s−1) to 0.5 m (0.10 × 1010 photons cm−2 s−1). Our study demonstrates that the BI of G. spinifera increases with increase in mechanical stimuli and decreases with increase in distance from the stimuli.

Microbes play a central role in the decomposition and remineralization of organic matter and recy... more Microbes play a central role in the decomposition and remineralization of organic matter and recycling of nutrients in aquatic environments. In this study, we examined the influence of physical, chemical and biological parameters on the rate of bacterial and viral production with respect to primary production over a diurnal period in Cochin estuary. Time–series measurements were made every 2 hours for 12 hours (6 AM-6 PM) during periods of low and high salinities. The light intensity as photosynthetically active radiation (PAR), temperature, salinity, nutrients like NO3-N, SiO4-Si, PO4-P and chlorophyll a (Chl a) were measured along with bacterial production (BP), viral production (VP) and net primary production (NPP). NPP showed a strong positive correlation with light and Chl a (r2 = 0.56 and 0.47 respectively), while VP showed a strong positive correlation with light, salinity and Chl a (r2 = 0.37, 0.58 and 0.37 respectively), and negative correlation with BP (r2 =- 0.39) at P ≤ ...

Environmental Science and Pollution Research

Mud banks and upwelling are two important oceanographic features occurring along the southwest co... more Mud banks and upwelling are two important oceanographic features occurring along the southwest coast of India during the southwest monsoon period. The study region, Alappuzha lying on the southwest coast of India, is unique due to the co-existence of upwelling and mud banks during the monsoon (MON) season. Water samples were collected from three stations, M1, M2, and M3, from April to September 2014, at weekly/biweekly intervals to determine the total bacterial abundance, viable prokaryotic counts, and total plate counts, along with measurements on physico-chemical parameters. For determining the heterotrophic culturable bacterial diversity, water samples were collected during two seasons, monsoon and pre-monsoon (PRM), from three stations. Water samples were inoculated into two non-selective broths for enrichment, DNA was extracted, and next-generation sequencing analysis was performed using Illumina Miseq sequencing. The sequence analysis revealed that dominant communities were Proteobacteria, followed by Firmicutes and Fusobacteria. Proportions of Fusobacteria increased during monsoon and proportions of Firmicutes were high in premonsoon season. Among Proteobacteria, Gammaproteobacteri is presented more than 99% of all the classes, irrespective of seasons. Vibrio was the most dominant genus during both seasons. The presence of anaerobic genera such as Propionigenium and Cetobacterium at all the stations during MON indicated the presence of upwelled waters. The genus Stenotrophomonas was observed in the M2 station alone. This study provides an overview of the culturable heterotrophic bacterial communities in a region in the southeastern Arabian Sea with coexisting mud banks and upwelling. The results of this study were compared with a published report on culture-independent bacterial diversity (from environmental DNA) from the same region. The study demonstrates that the use of culture media underrepresented the phylogenetic diversity and selectively enriched the class Gammaproteobacteria alone.

Aquatic Ecology, 2021

LWT

Abstract Seafood contamination with Salmonella enterica is a public health concern. The objective... more Abstract Seafood contamination with Salmonella enterica is a public health concern. The objective of this study was to investigate the survivability of Salmonella enterica serotype Typhimurium in fish and shrimp subjected to chilled (1 ± 2 °C) and frozen storage (−18 ± 2 °C). Bombay duck fish (Harpadon nehereus) and shrimp (Parapenaeopsis stylifera) were surface inoculated with 8 and 4 log CFU/g levels of S. Typhimurium. Survivability was studied by surface plating method on Salmonella-specific selective agar at regular intervals. In fish and shrimp inoculated with 8 log CFU/g and stored at −18 °C, viable counts could be detected for up to 90 days. At lower inoculation level of 4 log CFU/g, Salmonella was viable up to 60 days in frozen fish, while in frozen shrimp the bacterium could survive for only 15 days. In fish and shrimp stored in ice for 15 days, Salmonella showed 1–2 log CFU/g reduction in counts irrespective of initial inoculation levels. The results of this study suggest that the survival behaviour of Salmonella is influenced by the seafood matrix, temperature of storage and the population density of the bacterium itself. Therefore, strict monitoring of handling and storage procedures is necessary to control the processes that foster the survival and multiplication of Salmonella in the seafood chain.