Adaptation of chemosynthetic microorganisms to elevated mercury concentrations in deep-sea hydrothermal vents

Abstract

The response of deep-sea vent microorganisms to mercury (Hg) was investigated through measurements of total Hg (THg) concentrations in hydrothermal fluids from diffuse and focused flow vents on the East Pacific Rise at 9uN and the estimations of the proportion of Hg-resistant chemosynthetic thiosulfate-oxidizing microbes in a representative subset of diffuse flow fluids. Fluids were enriched in THg, with concentrations ranging from 15 to 445 pmol L21 and 3.5 6 0.1 to 11.0 6 0.8 nmol L21 in diffuse and focused flow emissions, respectively. In diffuse flow samples, most probable numbers (MPN) indicated that 0.25–24.6% of the total chemosynthetic thiosulfateoxidizing bacteria were resistant to Hg. The highest resistance levels were observed in samples with the highest THg concentrations, indicating that adaptation to life with toxic Hg had occurred in the diffuse flow environment. High THg concentrations in vent emissions and adaptation to Hg among chemosynthetic vent microbes indicate that (1) Hg in vent emissions may contribute to the oceanic Hg mass balance, and (2) activities of chemosynthetic microbes may mobilize solid-phase Hg in metal sulfide and contribute to Hg detoxification in deep-sea diffuse flow vents. Thus, the activities of chemosynthetic microbes may be critical to the mobility, geochemical cycling, and toxicity of Hg in the vent ecosystem.