Bacterial and archaeal communities in deep sea waters near the Ninetyeast Ridge in Indian Ocean

Depth-dependent distribution patterns of bacterial and archaeal communities in deep sea water column around the Ninety east Ridge in the Indian Ocean were investigated using 16 S rRNA gene profiling.Sampling was conducted at the northern Ninety east Ridge(1°59.89’N-9°59.70’S,87°58.90’E-88°00.03 ’E)from September to November 2016 where samples were collected from the bathyal(1 000 m) to bathypelagic depths(>4 000 m) in four different stations.A total of 1 565 405 clean data falling into 6 712 bacterial OTUs and 1 452 727 clean data falling into 806 archaeal OTUs based on 97% simlarity level were analyzed.Most of the bacterial 16 S rRNA gene sequences were affiliated with Gammaproteobacteria,followed by Alphaproteobacteria and Bacteroidia.The archaeal 16 S rRNA gene sequences mostly affiliated to Nitrososphaeria(Thaumarchaeota) dominated with relative abundances ranging from 52.68% to 97.2%,followed by Thermoplasmata(Euryarchaeota).Vertical partitioning of bacterial and archaeal communities among different water layers was observed.Canonical correspondence analysis(CCA) and Spearman’s correlations revealed that depth(P=0.003),dissolved oxygen(P=0.019),and nitrite(P=0.033) were the main environmental factors affecting bacterial community structure at genus level in the Ninetyeast Ridge.On the other hand,the first two CCA axes accounted for 74.4% of the explained total variance,it seems that the archaeal communities at genus level were heavily influenced by the environmental variables including depth,dissolved oxygen(DO),nitrite,salinity,phosphate,ammonia,nitrate,and silicate,but none of them exhibited any significant correlation on the structuring(P>0.1).