Browsing by Author "Alok Kumar Ravi"

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Dynamics of microcystin production and quantification of potentially toxigenic Microcystis sp. using real-time PCR
(Elsevier Ltd, 2012) Ankita Srivastava; Gang-Guk Choi; Chi-Yong Ahn; Hee-Mock Oh; Alok Kumar Ravi; Ravi Kumar Asthana
Cyanobacterial blooms in eutrophied water body are generally composed of various genotypes with or without microcystin-producing genes (mcy gene cluster). Thus there is a need for quantification of potent toxin producing strains. The present study aimed at identifying microcystin variants and its producer strains in Durgakund pond, Varanasi, India, based on quantification of cpcBA-IGS and mcyA (condensation domain) genes using real-time PCR and LC-MS. Increase in microcystin concentrations was correlated with increase in mcyA copy number and the level of pigments (chlorophyll a, phycocyanin and carotenoids). Also, selected environmental factors (water temperature, light irradiance, rainfall, pH, N and P) and the concentration of microcystin variants (MC-LR, -RR and -YR) were also assessed in samples during May 2010 to April 2011 to establish the possible correlation among these parameters. Nutrients favored cyanobacterial bloom but it could not be correlated with the levels of microcystin variants and seemed to be geographically specific. Microcystis sp. dominant in the pond comprised potentially toxigenic cells. The ratio of potentially toxigenic Microcystis sp. to that of total Microcystis sp. ranged from 0% to 14%. Such studies paved the way to identify and quantify the most potent microcystin producer in the tropical aquatic body. © 2011 Elsevier Ltd.
Microcystin Biosynthesis and mcyA Expression in Geographically Distinct Microcystis Strains under Different Nitrogen, Phosphorus, and Boron Regimes
(Hindawi Limited, 2016) Ankita Srivastava; So-Ra Ko; Chi-Yong Ahn; Hee-Mock Oh; Alok Kumar Ravi; Ravi Kumar Asthana
Roles of nutrients and other environmental variables in development of cyanobacterial bloom and its toxicity are complex and not well understood. We have monitored the photoautotrophic growth, total microcystin concentration, and microcystins synthetase gene (mcyA) expression in lab-grown strains of Microcystis NIES 843 (reference strain), KW (Wangsong Reservoir, South Korea), and Durgakund (Varanasi, India) under different nutrient regimes (nitrogen, phosphorus, and boron). Higher level of nitrogen and boron resulted in increased growth (avg. 5 and 6.5 Chl a mg/L, resp.), total microcystin concentrations (avg. 1.185 and 7.153 mg/L, resp.), and mcyA transcript but its expression was not directly correlated with total microcystin concentrations in the target strains. Interestingly, Durgakund strain had much lower microcystin content and lacked microcystin-YR variant over NIES 843 and KW. It is inferred that microcystin concentration and its variants are strain specific. We have also examined the heterotrophic bacteria associated with cyanobacterial bloom in Durgakund Pond and Wangsong Reservoir which were found to be enriched in Alpha-, Beta-, and Gammaproteobacteria and that could influence the bloom dynamics. © 2016 Ankita Srivastava et al.
Temporal variations in microcystin-producing cells and microcystin concentrations in two fresh water ponds
(Elsevier Ltd, 2015) Shweta Singh; Pankaj Kumar Rai; Rocky Chau; Alok Kumar Ravi; Brett A. Neilan; Ravi Kumar Asthana
The relationship between microcystin production, microcystin-producing cyanobacteria, including Microcystis spp., and various biological and physicochemical parameters in Sankuldhara and Lakshmikund, situated in the same geographical area was studied over a period of 1.5 years. Seasonal variation in cyanobacterial 16S rRNA, Microcystis spp. 16S rRNA, mcyA and mcyB genes were quantitatively determined by real-time PCR. Microcystis was the dominant microcystin producer in both study sites constituting 67% and 97% of the total microcystin-producing cyanobacteria at Sankuldhara and Lakshmikund, respectively. Microcystin concentrations were 2.19-39.60μg/L and 15.22-128.14μg/L at Sankuldhara and Lakshmikund, respectively, as determined by LC-MS. Principal component analysis revealed a strong positive correlation between microcystin concentration and the copy number of mcyA and mcyB, chlorophyll a and cyanobacterial biomass at both sites. The higher microcystin concentrations in Lakshmikund pond were attributed to the high copy number of mcy genes present coupled with the pond's eutrophication status, as indicated by high total algal biomass, high chlorophyll a content, high nutrient load and low DO. Therefore, a significant difference in microcystin concentrations, correlating with these various biological and physicochemical parameters, confirms the importance of local environmental variables in the overall regulation of microcystins production. © 2014 Elsevier Ltd.