Bacterial response to contrasting geochemistry in the sediments of central Indian Ocean basin

Abstract

The latitudinal differences in geochemical and physiographic nature could evoke varied biological/microbiological response in the deep-sea benthic ecosystem of the Central Indian Ocean. Sediment cores have been examined along latitudinal gradient as a part of the Polymetallic Nodules- Environmental Impact Assessment Environmental Variability Data Collection (PMN-EIA-EVDC) programme. Two such examples of geochemically contrasting cores namely, TVBC-26 and TVBC-08R. Core TVBC-26 (10 degrees S, 75.5 degrees E) is more terrigenously influenced and falls in the siliceous sediment realm and has a relatively higher total organic carbon content (0.37%) are presented. Core TVBC-08R (16 degrees S, 75.7 degrees E) falling in the pelagic red clay realm down south is away from the influence of the terrigenous influx and has a lesser total organic carbon value (0.22%). Though the total abundance of bacteria was one order higher in TVBC-08R (1.4x10 super(9)) as compared to TVBC-26 (7.2x10 super(8)), the anaerobic viability was one order high in TVBC-26. The viability of bacteria under aerobic condition was marginally high in TVBC-08R. Cells were generally less than equal to 1mu m in core 08R and ranged from 1.5-1.8 mu m in core 26. Retrievability of bacteria was in the same order (10 super (4).g super(-1)) on different strengths of ZoBell Marine agar suggesting that the bacteria were nutritionally more versatile in core TVBC-08R. Besides, the retrievability of nitrifier was also one order more at this station. Super(14) C uptake at 5 degrees C for 30 hrs showed that core TVBC-08R exhibited more autotrophic potential with DPM values of 478+395. g super(-1) as compared to only 17 + or - 4 g super(-1) in core TVBC-26. Thus, under the influence of nutrient starved North Atlantic Deep-Waters the bacterial community at TVBC-08R are nutritionally more flexible as compared to that at TVBC-26, which is bathed by the nutrient-rich Antarctic Bottom Waters.