Occurrence of large fractions of mercury-resistant bacteria in the Bay of Bengal.pdf

RESEARCH COMMUNICATIONS CURRENT SCIENCE, VOL. 91, NO. 3, 10 AUGUST 2006 368 *For correspondence. (e-mail: jaysankarde@) Occurrence of large fractions of mercury-resistant bacteria in the Bay of Bengal De Jaysankar1,2,* and N. Ramaiah1 1Biological Oceanography Division, National Institute of Oceanography, Dona Paula, Goa 403 004, India 2Present address: Graduate School of Kuroshio Science, Kochi University, Nankoku, Kochi 783 8502, Japan As insights from tolerance responses of native microflora are useful in deciphering their involvement in biogeo- chemical cycling of heavy metals, we enumerated mer- cury-resistant bacteria (MRB) using sea water nutrient agar medium amended with 10 ppm Hg from oceanic and coastal waters of the Bay of Bengal (BOB) during the summer monsoon (July–August 2001) period. MRB were present in all samples and, intriguingly, the MRB per cent based on total viable counts (TVC) in- creased significantly (r = 0.86; P 0.001; df = 44) with depth. On an average, MRB contributed to over 20% of TVC on the surface, 12% at 100 m, 35% at 500 m and a staggering 49% at 1000 m. The fact that a major portion of the natural, culturable bacterial flora was mercury-resistant from the offshore regions of the BOB points to the global nature of mercury pollution. The higher percentages of MRB in the offshore waters of the BOB might signify the already prevalent ad- verse impact of heavy metals on the metabolic per- formance of heterotrophic microflora. Keywords: Bay of Bengal, extremophiles, mercury- resistant bacteria, mercury pollution, total viable count. OBSERVATIONS on the occurrence and distribution of na- tive bacteria capable of metal tolerance are of relevance in microbial ecology to understand the extent of metal pollution as well as to reflect on the ability of such native forms to exist and carry on with their metabolic func- tions1,2. Many human activities have a negative impact on several biological proc