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Bacterial community structure and functional diversity in subsurface seawater from the western coastal ecosystem of the Arabian Sea, India

Kumar, Raghawendra, Mishra, Avinash, Jha, Bhavanath
Gene 2019 v.701 pp. 55-64
Firmicutes, bacteria, bacterial communities, biochemical oxygen demand, biochemical pathways, coastal ecosystems, coasts, color, community structure, correspondence analysis, dissolved oxygen, functional diversity, gamma-Proteobacteria, habitats, inorganic carbon, oxygen, pH, phylogeny, principal component analysis, quantitative polymerase chain reaction, reverse transcriptase polymerase chain reaction, salinity, seawater, temperature, total dissolved solids, total organic carbon, Arabian Sea, India
The present study revealed the spatial variability of bacteria in relation to physicochemical variations at four different locations (Diu - DIU, Veraval - VER, Porbandar - POR and Okha - OKH) along the Gujarat coast (Arabian Sea, India). The natural habitat was analyzed for temperature, salinity, pH, total dissolved solids, total organic content, total inorganic content, biological oxygen demand, conductivity and total dissolved oxygen. The lowest salinity and conductivity were observed at the VER site, whereas the highest salinity and conductivity were measured with OKH samples. In contrast, the pH was slightly alkaline at all of the sites. The VER site contained the maximum total dissolved solids (TDS), total carbon (TC), total organic carbon (TOC), and total inorganic carbon (TIC), while OKH showed the maximum dissolve oxygen (DO), biological oxygen demand (BOD), pH, temperature, conductivity, and salinity. The physicochemical characteristics showed that the Gujarat coast is alkaline and has a nutrient heterogeneous nature. Average well color development (AWCD) values, calculated using Biolog EcoPlates, showed that the microbial community from VER contained the highest metabolic activities and could metabolize all 31 substrates, followed by DIU > OKH > POR samples. In contrast, the abundance of the bacterial community, determined by qRT-PCR, was maximum in VER samples, followed by OKH > POR > DIU samples. The Shannon and Simpson indices showed that DIU, POR and OKH seawater clone libraries were more diverse. Furthermore, Chao estimator revealed the high diversity of POR and DIU clone libraries. Interestingly, DIU and OKH did not share any common operational taxonomic units (OTUs), and overall, the maximum bacterial diversity was observed with the POR seawater sample. Moreover, these observations were supported by statistical analysis, such as canonical correspondence analysis (CCA) and principal component analysis (PCA). The molecular phylogeny revealed the dominance of Proteobacteria followed by Firmicutes. Within the Proteobacteria phylum, most of the sequences were affiliated with the Gammaproteobacteria class. In total, about 726 OTUs were observed from all four sites which covers 59.79% DIU, 87.5% VER, 50% POR and 98.83% OKH of samples. This study is the first report to describe physicochemical attributes and the bacterial diversity of the coastal area of Gujarat. The study will provide useful insights about bacterial diversity, distribution, and abundance, as well as their relationships with the habitat.