A microbiological study of Guaymas Basin high temperature hydrothermal vents

Abstract

Water samples and suspended particulate matter were collected from three high temperature (156–319°C) hydrothermal vents in the Guaymas Basin during July 1985, and were analysed for a variety of chemical constituents and for the presence of viable microorganisms. Our results indicate that black smoker fluids (> 150°C) are devoid of recognizable bacteria and contain negligible concentrations of ATP (<10 ng 1 -1) and low concentrations of particulate organic matter. In contrast, vent water samples collected in the hydrothermal plume at a distance of only 25 cm from the point of hot fluid discharge contain a diverse, metabolically active bacterial assemblage, high ATP concentrations (up to 372 ng 1 -1) and high concentrations of particulate organic carbon and nitrogen (up to 999 and 163 μg 1 -1, respectively). The hottest waters (> 150°C) displayed a low, but measurable level of metabolic activity (incorporation of 3H-adenine and 14C-glutamate) at temperatures ranging from 25 to 80°C, 1 atm with maximal activity at 45°C. The maximum rate of incorporation, however, was only ∼ 1% of the activity measured in the samples collected in the hydrothermal plume. The strong metabolic preference for mesophilic growth temperatures (45°C) argues against a high temperature origin. Thermophilic sulfur-respiring bacteria were isolated from a variety of source materials including black smoker vent waters (112–319°C). All positive enrichments grew at 80°C, but none survived at temperatures in excess of 93°C. We conclude that these bacterial cells did not originate from the high temperature hydrothermal vent waters. Two different sample devices (reffered to as vent cap and smoker poker) were designed and employed during in situ collection-incubation experiments. Neither the vent cap attachment-colonization experiment nor the smoker poker collection device revealed the existence of bacterial cells in the black smoker fluids, despite evidence for a significant bacterial population in the hydrothermal plume. Our field and laboratory results indicate that thermophilic and mesophilic bacteria observed in hydrothermal vent plumes are not derived from the hot hydrothermal fluids but must originate in peripheral habitats.