Growth yields of Desulfotomaculum orientis with hydrogen in chemostat culture

Abstract

Desulfotomaculum orientis (strain Singapore 1) was grown autotrophically with H2+CO2 and sulfate, thiosulfate or sulfite as electron acceptor in sulfide- and pH-controlled continuous culture. Under sulfate-limiting conditions real growth yields of up to 9.7 g cell dry mass per mol sulfate were obtained. Electron acceptor limitation resulted in the excretion of up to 14.5 mmol acetate per liter, formed by reduction of CO2 with H2. Acetate production was not coupled to an increase of growth yields: under hydrogen-limiting conditions only 1.6 mmol acetate per liter was produced, and even higher growth yields of up to 12,4 g cell dry mass per mol sulfate were obtained. With thiosulfate or sulfite as electron acceptor growth yields increased up to 17.9 g cell dry mass per mol electron acceptor. Growth yields were not simply correlated with the growth rate, and did not allow the determination of maintenance coefficients and the extrapolation to maximal yields at infinite growth rate (Ymax). The maximal growth rates (μmax) with sulfate and thiosulfate were 0.090 and 0.109 h-1, respectively, if cells were grown continuously in sulfidostat culture under nonlimiting conditions.