Bacterial response to contrasting geochemistry in the sediments of Central Indian Ocean Basin

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. We present here two such examples of geochemically contrasting cores namely, TVBC-26 and TVBC- 08R. Core TVBC-26 (10°S, 75.5°E) is more terrigenously influenced and falls in the siliceous sediment realm and has a relatively higher total organic carbon content (0.37%). Core TVBC-08R (16°S, 75.7°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 (1.4x109) as compared to TVBC -26 (7.2x10 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 < 1µm in core 08R and ranged from 1.5-1.8µm in core 26. Retrievability of bacteria was in the same order (104.g-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. 14C uptake at 5°C for 30hrs showed that core TVBC-08R exhibited more autotrophic potential with DPM values of 478 +395. g-1 as compared to only 17+ 4. g-1 in core TVBC-26. Thus, under the influence of nutrient starved North Atlantic Deep-Waters (28) 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 (9).