Diversity, structure, and distribution of bacterioplankton and diazotroph communities in the Bay of Bengal during the winter monsoon

Abstract

The Bay of Bengal (BoB) is conventionally believed to be a low productive, oligotrophic marine ecosystem, where the diazotroph communities presumed to play a vital role in adding “new” nitrogen through the nitrogen fixation process. However, the diazotroph communities in the oceanic region of the BoB are still poorly understood though it represents most of the seawater volume. The present study investigated a detailed account of the bacterioplankton community structure and distribution in the oceanic BoB during the winter monsoon using high throughput sequencing targeting the 16S rRNA and nifH genes. Our study observed diverse groups of bacterioplankton communities in the BoB including both cyanobacterial and non-cyanobacterial phylotypes. Cyanobacteria (Prochlorococcus spp. and Synechococcus spp.) and Proteobacteria (mainly α-, γ-, and δ-Proteobacteria) were the most abundant groups within the bacterial communities, possessing differential vertical distribution patterns. Cyanobacteria were more abundant in the surface waters, whereas Proteobacteria dominated the deeper layers (75 m). However, within the diazotroph communities, Proteobacteria (mainly γ-Proteobacteria) were the most dominant groups than Cyanobacteria. Function prediction based on PICRUSt revealed that nitrogen fixation might more active to add fixed nitrogen in the surface waters, while nitrogen removal pathways (denitrification and anammox) might stronger in deeper layers. Canonical correspondence analysis (CCA) indicated that temperature, salinity, and silicate were major environmental factors driving the distribution of bacterial communities. Additionally, phosphate was also an important factor in regulating the diazotroph communities in the surface water. Overall, this study provided detailed information on bacterial communities and their vital role in the nitrogen cycles in oligotrophic ecosystems.

Article Seasonal Surges in Bacterial Diversity along the Coastal Waters of the Eastern Arabian Sea

“…To date, there are no reports on the abundance of Prochlorococcus in the coastal waters of Kochi [58]. Similar community structure has been previously observed during winter monsoon period of Bay of bengal in which Proteobacteria represented the highest diversity and largest fractions [59]. Candidatus Nitrosopelagicus, Nitrosopumilus show increased abundance from south to north.…”

Diazotrophy in the Indian Ocean: Current understanding and future perspectives

“…A recent study showed that gammaproteobacterial diazotrophs are negatively influenced by temperature during the NEM in the BoB and positively correlated with silicate, suggesting a possible association with diatoms (Shao and Luo 2022). Instead, in the BoB alpha‐ and betaproteobacterial diazotrophs are positively correlated to temperature (Wu et al 2022).…”

“…In other seasons, the BoB harbors cyanobacterial representatives including Trichodesmium (particularly during the IM), Richelia , Katagnymene , UCYN‐A, and UCYN‐B. Because Trichodesmium typically grows in oligotrophic and stratified epipelagic waters (Capone et al 1997), the high turbulence and strong wind conditions observed in the BoB during the NEM and SWM may be unfavorable for their growth (Wu et al 2022). While cyanobacteria predominate at the surface, alpha‐ and betaproteobacteria are significantly more abundant at deeper levels (based on the relative abundance of ASVs) (Appendix S2; Fig.…”

“…While cyanobacteria predominate at the surface, alpha‐ and betaproteobacteria are significantly more abundant at deeper levels (based on the relative abundance of ASVs) (Appendix S2; Fig. S6; Wu et al 2022).…”

Phylogenetic diversity and functional potential of large and cell-associated viruses in the Bay of Bengal

“…Consequently, the microbial communities at the foundation of the BoB ecosystem remain poorly understood. A few recent studies have looked at bacterial diversity through 16S amplicon sequencing, but very few have looked at the functional potential and interactions of the microbial communities in this region ( 10 , 11 ). Among the studies that have attempted to look at microbial diversity through metagenomics, all have been focused on sediment bacteria in the deep sea ( 12 ), with little or no efforts targeted toward understanding the microbiota of surface water communities, the communities closely associated with corals, seagrass, and mangroves using similar approach.…”