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Rising demand in the aquaculture sector tends towards finding innovative ways to promote better yield and profitability. Benthic soil microbiota can provide an insight into the potent opportunistic fish pathogens as well as probiotics present in the aquaculture system. This study reports the seasonal diversity and abundance of fifteen culturable pathogenic bacterial strains belonging to the genera of Comamonas, Aeromonas, Providencia, Klebsiella, Escherichia, Acinetobacter, Serratia, Stenotrophomonas, Staphylococcus, and Enterobacter along with nine probiotic strains native to genera of Bacillus and Pseudomonas isolated from an aquaculture farm benthic soil, located in East Kolkata Wetlands, West Bengal, India. Strains are isolated using traditional microbial culture methods and tested for their antimicrobial susceptibility against commonly available antibiotics. 16S rDNA analysis was done for the identification of the strains and the establishment of their phylogenetic relationships. Among the isolates, B. pumilus strain S8 in the pre-monsoon sample, E. coli strain M2aR1 in the monsoon sample, and A. hydrophila strain P6dF1 in the post-monsoon sample were the most abundant having MPN counts of 275±21 x 106 CFU/gram dry soil, 278±18 x 106 CFU/gram dry soil, and 321±28 x 106 CFU/gram dry soil respectively. Data on the temporal diversity, abundance, and drug-susceptibility of prokaryotic fish-pathogens and probiotics can be used to formulate measures for sustainable aquaculture practices with reduced maintenance costs.

Benzene is an omnipresent aromatic hydrocarbon of the environment and the pollution caused by it is a matter of great public concern. The study was designed to isolate, characterize and identify aerobic bacterial strains capable of benzene degradation from petroleum-contaminated soils of Kolkata, India. Three strains, designated as MKB1b, MKB2a and MKB2d were found to be able to degrade benzene, as the only source of carbon and energy. All the isolated strains had an optimal growth pH of 8.0, and grew best at 37°C to 40°C. Based on their molecular (16S rDNA sequence) characterization, all of the three bacterial strains were phylogenetically similar to the genus Escherichia. Strains MKB2a and MKB2d were identified as Escherichia coli, whereas Strain MKB1b was identified as Escherichia fergusonii; all three sequences were submitted to GenBank bearing accession numbers MK970556, MK970574, MK970557 respectively. This study is the first evidence of isolation, characterization and identification of aerobic benzene-degrading Escherichia spp. from petroleum-contaminated sites of an urban landscape in India. All of these isolated strains may be considered as potent candidates for the bioremediation of urban environment polluted with petroleum products.

The present study investigates the cellulolytic potential of three prokaryotic strains belonging to genus Bacillus isolated from the benthic soil of two aquaculture farms in East Kolkata Wetlands. For the purpose of identification and phylogenetic analyses, biochemical characterization of these three strains were performed followed by molecular characterization of 16S rRNA sequences. Maximum cellulolytic potential was found in Bacillus cereus Strain SWA6a for both Exo - b,1-4- glucanase and Endo - b,1-4- glucanase with an activity of 0.08214 ± 0.00412 and 0.11263 ± 0.00478 IU ml-1min-1 respectively. The enzyme activity ranged from 0.06112 to 0.08214 IU ml-1min-1 for Exo - b,1-4- glucanase and 0.10018 to 0.11263 IU ml-1min-1 for Endo - b,1-4- glucanase. Degradation of free insoluble cellulose ranged from 55 to 63% within a time span of 96 hours in pH 6.8 – 7.2 when incubated at 37°C. Overall, the cellulolytic activity of the isolated strains may have strong implications in the field of biological conversion of cellulose-containing municipal wastes, agricultural and forestry wastes. These isolates maintain the equilibrium of the aquaculture pond by maintaining the biogeochemical cycle of carbon and hence has the prospect to be used for bioaugmentation purposes as a step towards a microbial-based aquaculture method.