The Composition and Primary Metabolic Potential of Microbial Communities Inhabiting the Surface Water in the Equatorial Eastern Indian Ocean

Comparative analysis of microbiome inhabiting oxygenated and deoxygenated habitats using V3 and V6 metabarcoding of 16S rRNA gene

We examine how oxygen levels and the choice of 16S ribosomal RNA (rRNA) tags impact marine bacterial communities using Next-Generation amplicon sequencing. Analyzing V3 and V6 regions, we assess microbial composition in both Oxygen minimum zones (OMZ) and non-OMZ (NOMZ) areas in the Arabian Sea (AS) and the Central Indian Ocean basin (CIOB) respectively. Operational taxonomic units (OTUs) at 97% similarity showed slightly higher richness and diversity with V6 compared to V3. Vertical diversity patterns were consistent across both regions. NOMZ showed greater richness and diversity than OMZ. AS and CIOB exhibited significant differences in bacterial community, diversity, and relative abundance at the order and family levels. Alteromonadaceae dominated the OMZ, while Pelagibacteraceae dominated the NOMZ. Synechococcaceae were found exclusively at 250 m in OMZ. Bacteria putatively involved in nitrification, denitrification, and sulfurylation were detected at both sites. Dissolved oxygen significantly influenced microbial diversity at both sites, while seasonal environmental parameters affected diversity consistently, with no observed temporal variation.

Depth-dependent microbial metagenomes sampled in the northeastern Indian Ocean

The northeastern Indian Ocean exhibits distinct hydrographic characteristics influenced by various local and remote forces. Variations in these driving factors may alter the physiochemical properties of seawater, such as dissolved oxygen levels, and affect the diversity and function of microbial communities. How the microbial communities change across water depths spanning a dissolved oxygen gradient has not been well understood. Here we employed both 16S rDNA amplicon and metagenomic sequencing approaches to study the microbial communities collected from different water depths along the E87 transect in the northeastern Indian Ocean. Samples were collected from the surface, Deep Chlorophyll Maximum (DCM), Oxygen Minimum Zone (OMZ), and bathypelagic layers. Proteobacteria were prevalent throughout the water columns, while Thermoproteota were found to be abundant in the aphotic layers. A total of 675 non-redundant metagenome-assembled genomes (MAGs) were constructed, spanning 21 bacterial and 5 archaeal phyla. The community structure and genomic information provided by this dataset offer valuable resources for the analysis of microbial biogeography and metabolism in the northeastern Indian Ocean.

Subsurface Bacterioplankton Structure and Diversity in the Strongly-Stratified Water Columns within the Equatorial Eastern Indian Ocean

The consequences of climate change may directly or indirectly impact the marine biosphere. Although ocean stratification has been recognized as one of the crucial consequences of ocean warming, its impacts on several critical aspects of marine microbes remain largely unknown in the Indian Ocean. Here, we investigate the effects of water stratification, in both surface and subsurface layers, on hydrogeographic parameters and bacterioplankton diversity within the equatorial eastern Indian Ocean (EIO). Strong stratification in the upper 200 m of equatorial EIO was detected with evidential low primary productivity. The vertical bacterioplankton diversity of the whole water columns displayed noticeable variation, with lower diversity occurring in the surface layer than in the subsurface layers. Horizontal heterogeneity of bacterioplankton communities was also in the well-mixed layer among different stations. SAR11 and Prochlorococcus displayed uncharacteristic low abundance in the surface water. Some amplicon sequence variants (ASVs) were identified as potential biomarkers for their specific depths in strongly-stratified water columns. Thus, barriers resulting from stratification are proposed to function as an ‘ASV filter’ to regulate the vertical bacterioplankton community diversity along the water columns. Overall, our results suggest that the effects of stratification on the structure and diversity of bacterioplankton can extend up to the bathypelagic zone in the strongly-stratified waters of the equatorial EIO. This study provides the first insight into the effect of stratification on the subsurface microbial communities in the equatorial eastern Indian Ocean.

Microbial Diversity in the Indian Ocean Sediments: An Insight into the Distribution and Associated Factors

Indian Ocean is the third largest oceanic division of the world and shelter to a huge microbial diversity. These microbes play an important role in the metabolism of carbon, sulfur, nitrogen, and phosphorus in the ocean water. They are also major contributors of carbon fixing and sequestration, as much as terrestrial plants to achieve CO₂ emissions reduction. The prokaryotic community in the East Indian Ocean primarily comprises of heterotrophic bacteria like Alphaproteobacteria and Gammaproteobacteria, followed by Firmicutes and Actinobacteria. The Arabian Sea and the Bay of Bengal are typically characterized by presence of vast areas of oxygen minimum zones (OMZs) and have been witnessing a shift in the microbial diversity due to the changing conditions in the ocean water. Several canonical correspondence analyses reveal temperature, salinity, and phosphate levels as crucial environmental factors in propelling the distribution of diazotrophs. The viral consortia are dominated by the Caudovirales, an order of tailed bacteriophages. Due to the rapid change in the environmental factors such as topography, temperature, and sunlight contributing toward climate change, their role in sustaining the chemical composition of the ocean can be drastically affected especially with the evidence of several bacterial and fungal communities responding to latitudinal and temperature change. Therefore, we aim to critically review the status of microbial diversity in Indian Ocean to predict their response toward climate change as they are the sentinels of change in marine life and to understand the dynamics of microbial communities in the various locations of Indian Ocean.