In the wake of the findings that Antarctic krills concentrate heavy metals at ppm level, (Yamamoto et al. 1987), the Antarctic waters from the Indian side were examined for the incidence of metal and antibiotic-resistant bacteria during the austral summer (13th Indian Antarctic expedition) along the cruise track extending from 50 degrees S and 18 degrees E to 65 degrees S and 30 degrees E. The bacterial isolates from these waters showed varying degrees of resistance to antibiotics (Chloramphenicol, ampicillin, streptomycin, tetracycline and kanamycin) and metals (K(2)CrO(4), CdCl(2), ZnCl(2) and HgCl(2)) tested. Of the isolates screened, about 29% and 16% were resistant to 100 ppm of cadmium and chromium salt respectively. Tolerance to lower concentration (10 ppm) of mercury (Hg) was observed in 68% of the isolates. Depending on the antibiotics the isolates showed different percentage of resistance. Multiple drug and metal-resistance were observed. High incidence of resistance to both antibiotics and metals were common among the pigmented bacterial isolates. Increased resistance decreased the ability of bacteria to express enzymes. The results reiterate previous findings by other researchers that the waters of southern ocean may not be exempt from the spread of metal and antibiotic-resistance.

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Net nitrous oxide production and denitrification activity were measured in two mangrove ecosystems of Goa, India. The relatively pristine site Tuvem was compared to Divar which is prone to high nutrient input. Stratified sampling at 2 cm intervals within the 0-10 cm depth range showed that N 2 O production at both the locations decreased with depth. Elevated denitrification activity at Divar resulted in maximum production of up to 1.95 nmol N 2 O-N g -1 h -1 at 2-4 cm which was 3 times higher than at Tuvem. Detailed investigations to understand the major pathway contributing to nitrous oxide production carried out at Tuvem showed that incomplete denitrification was responsible for up to 43-93% of N 2 O production. N 2 O production rates closely correlated to nitrite concentration (n=15; r=-0.47; p<0.05) and denitrifier abundance (r=0.55; p<0.05) suggesting that nitrite utilisation by microbial activity leads to N 2 O production. Nitrous oxide production through nitrification was below detection affirming that denitrification is the major pathway responsible for production of the greenhouse gas. Net N 2 O production in these mangrove systems are comparatively higher than those reported from other natural estuarine sediments and therefore warrant mitigation measures.

In order to investigate whether geochemical, physiographic and lithological differences in two end-member sedimentary settings could evoke varied microbe-sediment interactions, two 25 cm long sediment cores from contrasting regions in the Central Indian Basin have been examined. Site TVBC 26 in the northern siliceous realm (10°S, 75AE5°E) is organic-C rich with 0AE3 ± 0AE09% total organic carbon. Site TVBC 08 in the southern pelagic red clay realm (16°S, 75AE5°E), located on the flank of a seamount in a mid-plate volcanic area with hydrothermal alterations of recent origin, is organic-C poor (0AE1 ± 0AE07%). Significantly higher bacterial viability under anaerobic conditions, generally lower microbial carbon uptake and higher numbers of aerobic sulphur oxidizers at the mottled zones, characterize core TVBC 26. In the carbon-poor environment of core TVBC 08, a doubling of the 14 C uptake, a 250 times increase in the number of autotrophic nitrifiers, a four-fold lowering in the number of aerobic sulphur oxidizers and a higher order of denitrifiers exists when compared with core TVBC 26; this suggests the prevalence of a potentially autotrophic microbial community in core TVBC 08 in response to hydrothermal activity. Microbial activity at the northern TVBC 26 is predominantly heterotrophic with enhanced chemosynthetic activity restricted to tan-green mottled zones. The southern TVBC 08 is autotrophic with increased heterotrophic activity in the deepest layers. Notably, the bacterial activity is generally dependent on the surface productivity in TVBC 26, the carbon-rich core, and mostly independent in TVBC 08, the carbon-poor, hydrothermally influenced core. The northern sediment is more organic sink-controlled and the southern sediment is more hydrothermal source-controlled. Hydrothermal activity and associated rock alteration processes may be more relevant than organic matter delivery in these deep-sea sediments. Thus, this study highlights the relative importance of hydrothermal activity versus organic delivery in evoking different microbial responses in the Central Indian Basin sediments.

The eastern Arabian Sea has a unique and permanent oxygen minimum zone (OMZ) that extends along the western continental margin of India. The sediment below this region is rich in organic matter. This study describes the bacterial community structure and diversity in OMZ sediments of the eastern Arabian Sea (AS) through 16S rRNA clone library analysis. Phylogenetic analysis of the sequences demonstrated that phylum Proteobacteria (52%), followed by Planctomycetes (12.7%), Chloroflexi and an unidentified bacterial group (8.8% each) were represented in the library. Deltaproteobacteria was the dominant class (62.5%) in phylum Proteobacteria with clones falling in orders Syntrophobacterales and Desulfovibrionales. Few minor phylogenetic groups, corresponding to Spirochetes, Firmicutes, Acidobacteria and Verrucomicrobia were found. Unidentified candidate groups falling in OP11, OP8 and OP3 were represented by 0.9, 2.9 and 3.9%, respectively and two clusters of the cloned sequences in this study showed very low identity to known sequences. This is the first report that discusses the phylogenetic groups in the OMZ sediments of eastern Arabian Sea individually and compares it with available data from marine hypoxic locales and water mass. LIBSHUFF statistics revealed high richness of the bacterial community of the Arabian Sea OMZ (AS-OMZ) compared to the other regions.

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