Antagonistic effect of Anabaena fertilissima CCC597 on pathogenic Vibrio cholerae propagating in association with cyanobacterial community in freshwater bodies of Eastern Madhya Pradesh

Various biodiversity indices revealed that Microcystis aeruginosa is a major bloom forming colonial cyanobacterium dominantly present in the examined two districts of Eastern Madhya Pradesh. Microcystis viridis, Microcystis panniformis and Microcystis botrys along with filamentous cyanobacteria Anabaena spp., Arthrospira major and Oscillatoria limosa/O. laetevirens were the other species present. Amplification of VCO1 and VCO139 choleragenic Vibrio cholerae strains in phytoplankton material revealed their association with cyanobacteria. VCO1 gene was amplified in five water bodies, and among them, one reservoir also displayed amplification of VCO139 gene. VCO1 and VCO139 genes were not amplified in three water bodies. All of them were infested with Anabaena spp. as the second largest phytoplankton constituent. It was hypothesized that Anabaena spp. produced some antibacterial metabolites with antagonistic property against V. cholerae. To prove this, colonies of V. cholerae on TCBS agar were isolated from those water bodies which displayed VCO1 and VCO139 gene amplification. Methyl Red test, Voges-Prauskaur test and arginine dehydrolase tests confirmed Vibrio. Further identification of V. cholerae was carried out by amplification of VCO1 and VCO139 genes in genomic DNA isolated from V. cholerae colonies. A hexane extractable metabolite extracted from lab culture of Anabaena fertilissima CCC597, a native of these lakes, was tested for its antagonizing effect on growth of V. cholerae strains O1 and O139. A “closed water system” was used to examine the effect of A. fertilissima cell mass on time-dependent population size of Vibrio. Upon such incubation, there was a steady decrease in the viable colony counts of V. cholerae.