Diversity of Bacterial Community in the Oxygen Minimum Zones of Arabian Sea and Bay of Bengal as Deduced by Illumina Sequencing.

Genevieve L Fernandes,Samir R Damare,Belle Damodara Shenoy

doi:10.3389/fmicb.2019.03153

Genevieve L Fernandes, Samir R Damare + Show 1 more

Open Access

https://doi.org/10.3389/fmicb.2019.03153

Copy DOI

Abstract

The Indian Ocean harbors oxygen minimum zones (OMZs) in the Arabian Sea and Bay of Bengal, with dissolved oxygen < 20 μM, located at the mid-depths of the water column. Till date, high-throughput sequence-data on depth-wise distribution of prokaryotic communities have rarely been reported from these OMZs. The present study aimed to characterize the prokaryotic diversity inhabiting Arabian Sea Time Series (ASTS) and India’s Idea 2 (II2) in the Arabian Sea, and Bay of Bengal Time Series (BoBTS) in the Bay of Bengal OMZs based on amplicon sequencing of 16S rRNA gene regions, along six sampled depths in the water column. High prokaryotic richness was observed in the Arabian Sea and Bay of Bengal samples. Operational taxonomic units (OTUs) in the range of 1249–3298 were identified, wherein, less prokaryotic diversity was observed at surface and within oxygen minimum depths. At phylum level, most OTUs were affiliated to Bacteroidetes, Chloroflexi, Cyanobacteria, Marinimicrobia, Planctomycetes, and Proteobacteria. Prokaryotic community differed between ASTS, II2 and BoBTS locations along varying physicochemical conditions. Predictive functional profiling of the bacterial communities suggested the involvement of abundant microbes in nitrogen and sulfur metabolism pathways. Bacterial isolates belonging to genera from the clades, δ-Proteobacteria and γ-Proteobacteria, described previously for their participation in biogeochemical cycling of N-and-S in the OMZs were reported from deoxygenated waters of both the basins. Bacteria involved in anammox such as Candidatus Scalindua were found to be relatively high at ASTS and II2 locations in the Arabian Sea. Further studies are required to ascertain the role of abundant bacteria along the dynamic oceanographic processes in the OMZs.

Highlights

Oxygen minimum zones (OMZs), termed as shadow zones, are regions where oxygen saturation in seawater is persistently low, i.e., below 20 μM (0.5 ml/L) at intermediate depths of the water column (∼100 to 1300 m) (Levin, 2003; Gilly et al, 2013)
The temperature decreased as the depth increased, while higher salinity was observed at surface sampled depth of Arabian Sea Time Series (ASTS) (36.9 PSU) and India’s Idea 2 (II2) (36.5 PSU) than Bay of Bengal Time Series (BoBTS) (34.1 PSU)
Dissolved oxygen (DO) profile of ASTS and BoBTS is typical of an oxygen minimum zones (OMZs), i.e., the surface and near bottom depths are well-oxygenated

Summary

Introduction

Oxygen minimum zones (OMZs), termed as shadow zones, are regions where oxygen saturation in seawater is persistently low, i.e., below 20 μM (0.5 ml/L) at intermediate depths of the water column (∼100 to 1300 m) (Levin, 2003; Gilly et al, 2013). Bacterial Community of Indian Ocean OMZs in the north, Eastern South Pacific (ESP) in the south; Arabian Sea (AS) in the west and Bay of Bengal (BoB) in the east. The AS-OMZ experiences intense low dissolved oxygen (DO) concentration of < 2 μM (0.05 ml/L) between 100 and 1000 m depth in the water column, while the BoB-OMZ has DO levels < 4 μM (0.1 ml/L) at mid depths in the water column. The difference in oxygen concentration between these two basins is just 2 μM, a large-scale denitrification and reducing of other electron acceptors takes place in AS, in contrast to BoB that inhibits denitrification rates by 50% (Naqvi, 2006; Johnson et al, 2019). The BoB is believed to be less productive than the AS, much contributed to the freshwater input from the rivers, which reduces the salinity on the surface, and induces stratification (Gomes et al, 2000; Madhupratap et al, 2003; Singh and Ramesh, 2015)

Methods

Results

Discussion

Conclusion