Microbial processes at the Lost City vent field, Mid-Atlantic Ridge

Abstract

Microbiological and biogeochemical measurements showed that the intensities of CO2 assimilation, methane oxidation, and sulfate reduction at the Lost City vent field (3° N) reach 3.8 µg C/(1 day), 0.06 µg C/(1 day), and 117 µg S/(1 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 µg C/(dm3 day), 0.02 µg C/(dm3 day), and 28000 µg S/(dm3 day), respectively. Bacterial mats of the second variety are formed by nonpigmented 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 µg C/(dm3 day), 5.8 µg C/(dm3 day), and 17000 µg S/(dm3 day), respectively. These data suggest the existence of subsurface microflora at the Lost City vent field.