Microbial processes at the lost city vent field, Mid-Atlantic Ridge

Microbiological and biogeochemical measurements showed that the intensities of CO2 assimilation, methane oxidation, and sulfate reduction at the Lost City vent field (30 degrees N) reach 3.8 mu g C/(1 day), 0.06 mu g C/(1 day), and 117 mu g S/(l day), respectively. On the surface of the carbonate structures occurring at this field, two varieties of bacterial mats were found. The first variety, which is specific to the Lost City alkaline vent field, represents jellylike bacterial mats dominated by slime-producing bacteria of several morphotypes. This mat variety also contains chemolithotrophic and heterotrophic microorganisms, either microaerobic or anaerobic. The intensities of CO2 assimilation, methane oxidation, and sulfate reduction in this variety reach 747 mu g C/(dm(3) day), 0.02 mu g C/(dm(3) day), and 28000 mu g S/(dm(3) day), respectively. Bacterial mats of the second variety are formed by nonpigniented filamentous sulfur bacteria, which are close morphologically to Thiothrix. The intensities of CO2 assimilation, methane oxidation, and sulfate reduction in the second mat variety reach 8.2 mu g C/(dm(3) day), 5.8 mu g C/(dm(3) day), and 17000 mu g S/(dm(3) day), respectively. These data suggest the existence of subsurface microflora at the Lost City vent field.