Nitrogen driven niche differentiation in bacterioplankton communities of northeast coastal Bay of Bengal

Abstract

The Bay of Bengal receives nitrogen inputs from multiple sources and the potential role of nitrogen-metabolizing microbial communities in the surface water is not well understood. The nitrogen budget estimate shows a deficit of 4.7 ± 2.4 Tg N yr-1, suggesting a significant role of dissolved organic nitrogen remineralization in fuelling ecosystem processes. Unravelling the process of remineralization leading to increasing concentrations of dissolved inorganic nitrogen (DIN) in coastal ecosystems such as mangroves require a better understanding of the composition of functional resident bacterioplankton communities. Bacterioplankton communities were elucidated from eight stations along different estuaries spanning west to east of northeast coastal Bay of Bengal to understand the influence of DIN on shaping these communities. The eight stations were differentiated into ‘low’ and ‘high’ DIN stations based on a DIN concentration, with five stations with High DIN concentration (>45 µM) and three stations with Low DIN concentration (<40µM). The V3-V4 region of 16S rRNA was amplified and sequenced to elucidate resident bacterioplankton community structure from environmental DNA. Proteobacteria, Bacteroidetes, and Firmicutes were the dominant bacterioplankton phyla across all stations. Nitrogen-fixing groups such as Nitrospirae, Lentisphaerae, Chloroflexi, and Planctomycetes make up about 1% of the bacterioplankton communities. Abundances of Spirochaetes and Tenericutes showed a positive correlation with DIN. Pseudomonadales, Alteromonadales, and Desulfovibrionales were found to distinctly vary in abundance between low and High DIN stations. Predicted metagenomic profiles from taxonomically derived community structures indicated bacterial nitrate-nitrite reductase to be negatively correlated with prevalent DIN concentration in High DIN stations but positively correlated in Low DIN stations. This trend was also consistent for genes encoding for nitrate/nitrite response regulators and transporter proteins. This indicates the need to delineate functional bacterioplankton community structures to better understand their role in influencing rates and fluxes of nitrogen within mangroves.

Phylogenetic diversity and functional potential of the microbial communities along the Bay of Bengal coast

“…Relatively higher abundance of the Flavobacteriaceae family in our study sites could indicate the availability of complex macromolecules in these coastal regions. These findings in the BoB confirm previous studies that showed the dominance of Proteobacteria and Bacteroidetes, of which Flavobacteriaceae and Rhodobacteraceae are a part of, in multiple other locations within the bay 13 , 90 .…”

Exploring Microbial Diversity and Functional Potential along the Bay of Bengal Coastline in Bangladesh: Insights from Amplicon Sequencing and Shotgun Metagenomics

“…As a part of the Indian Ocean, the third largest oceanic division of the world 80 , and being surrounded by three different countries, BoB provides ecological habitats and niches for an enormous diversity of microbial groups 13,81 . A recent study conducted by Ghosh et al (2022) revealed that the bacterioplankton community in multiple locations of BoB showed the dominance of Proteobacteria, Bacteroidetes, and Firmicutes as well as the nitrogen-fixing groups such as Nitrospirae, Lentisphaerae, Chloroflexi, and Planctomycetes 82 . Another metagenome-based study of deep-sea sediment samples from 3000m depth of BoB revealed the dominance of Proteobacteria followed by Bacteroidetes, Firmicutes, Cyanobacteria and Actinobacteria 13 .…”

Macrobenthic community of an anthropogenically influenced mangrove associated estuary on the East coast of India: An approach for ecological assessment

“…Such low DO can prolong hypoxia and affect major estuarine ecosystem-level processes, including fluxes and rates linked to carbon and nitrogen biogeochemical cycling. Therefore, maintaining the best possible conditions across the river basins, including coastal and offshore waters, is essential (Karydis and Kitsiou, 2013;Barletta et al, 2019) and crucial for ecosystem functioning and maintaining estuarine biodiversity (Ghosh et al, 2022). Fine sediment deposition is difficult in the regions where strong water currents persist (Mitchell, 2020).…”

“…In fact, for many estuaries on the east coast of India, premonsoon exhibit the most stressed conditions with excess and continuous accumulation of contaminants (Mitra et al, 2018). However, a good flush-out of pollutants is only possible during the monsoon season (Mulik et al, 2020a), aided further by a breakdown of contaminants owing to changing redox chemistry and consequences on benthicpelagic coupling (Ghosh et al, 2022).…”