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

Summary Hydrothermal fluids (341°C and 19°C) were collected < 1 m apart from a black smoker chimney and a tubeworm mound on the B oardwalk edifice at the E ndeavour S egment in the northeastern P acific O cean to study anaerobic microbial growth in hydrothermal mineral deposits. Geochemical modelling of mixed vent fluid and seawater suggests the mixture was anoxic above 55°C and that low H 2 concentrations (79 μmol kg −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°C fluid raising questions about its H 2 ‐dependent growth kinetics. Strain HR 11 grew at 40–77°C (T opt 72–75°C), pH 5–8.5 (pH opt 6–7) and 1–5% (wt vol −1 ) NaCl (NaCl opt 3–4%). The highest growth rates occurred when S 2 O 3 2− and S° were reduced to H 2 S . Modest growth occurred by NO 3 − reduction. Monod constants for its growth were K s of 30 μM for H 2 and K s of 20 μM for S 2 O 3 2− with a μ max of 2.0 h −1 . The minimum H 2 and S 2 O 3 2− concentrations for growth were 3 μM and 5 μM respectively. Possible sources of S 2 O 3 2− and S° are from abiotic dissolved sulfide and pyrite oxidation by O 2 .