Hydrogen and thiosulfate limits for growth of a thermophilic, autotrophic Desulfurobacterium species from a deep-sea hydrothermal vent

Hydrothermal fluids (341 degrees C and 19 degrees C) were collected <1m apart from a black smoker chimney and a tubeworm mound on the Boardwalk edifice at the Endeavour Segment in the northeastern Pacific Ocean to study anaerobic microbial growth in hydrothermal mineral deposits. Geochemical modelling of mixed vent fluid and seawater suggests the mixture was anoxic above 55 degrees C and that low H-2 concentrations (79molkg(-1) in end-member hydrothermal fluid) limit anaerobic hydrogenotrophic growth above this temperature. A thermophilic, hydrogenotrophic sulfur reducer, Desulfurobacterium strain HR11, was isolated from the 19 degrees C fluid raising questions about its H-2-dependent growth kinetics. Strain HR11 grew at 40-77 degrees C (T-opt 72-75 degrees C), pH 5-8.5 (pH(opt) 6-7) and 1-5% (wt vol(-1)) NaCl (NaClopt 3-4%). The highest growth rates occurred when S2O32- and S degrees were reduced to H2S. Modest growth occurred by NO3- reduction. Monod constants for its growth were K-s of 30M for H-2 and K-s of 20M for S2O32- with a (max) of 2.0h(-1). The minimum H-2 and S2O32- concentrations for growth were 3M and 5M respectively. Possible sources of S2O32- and S degrees are from abiotic dissolved sulfide and pyrite oxidation by O-2.