Community structure, taxonomic diversity and spatio-temporal variation of sediment and water bacteria in Bhitarkanika mangrove ecosystem, India

Bacterial diversity of Bhitarkanika mangrove was studied by both the culture-dependent and culture-independent methods. The variation of culture-dependent bacterial population with respect to different physico-chemical parameters was also observed seasonally (summer and monsoon) from five stations-Dangmal, Ekakula, Gupti, Habalikhati and Kalibhanjadiha. Overall, culture-dependent total heterotrophic bacteria varied from 2.16 +/- 0.5 to 168.25 +/- 1.73 x 10(3)cfu/g in sediment and 1.53 +/- 0.915 to 38.33 +/- 0.108 x 10(3)cfu/ml in water. Major regulatory factors for bacterial abundance of water were nitrate phosphate, conductivity, dissolved oxygen in different seasons while no such clear influence was observed on sediment bacterial abundance. Culture-dependent study revealed thatBacilli,GammaproteobacteriaandBetaproteobacteriawere dominant bacterial classes. Culture-independent study revealed that the operational taxonomic unit varied from 5077 to 21,207 in sediment and 14,213 to 17,501 in water. Majority of the bacterial community were found to be under the classGammaproteobacteriafollowed byAlphaproteobacteriaandBacilli. In sediment, highest and lowest species richness as well as evenness was recorded at Dangmal and Ekakula, respectively, while in water, both the parameters were more or less similar in all the sampling sites. Maximum species diversity was observed at Dangmal sediment (Shannon diversity index: 10.43) and Habalikhati water (Shannon diversity index: 7.45). Principal Coordinate Analysis (PCoA) revealed that Ekakula, Kalibhanjadiha and Gupti, Habalikhati sediment had similar species composition in culture-dependent and independent analysis, respectively. Dangmal sediment had the unique species composition, whereas bacterial species composition in water varied greatly within different sites in both the cases. This study depicts the highly rich bacterial diversity of Bhitarkanika.