Kinetics of CO2 fixation by Sulfurovum lithotrophicum 42BKTT: Medium optimization and tolerance of CO2 toxicity

Abstract

CO2 toxicity, ionic strength, and specific culture media components, such as thiosulfate have been reported to influence the growth of CO2-fixing autotrophic bacteria. In this study, a chemostat culture was used to determine the kinetics of CO2 fixation by S. lithotrophicum 42BKTT. The medium composition was determined to be capable of reaching a steady state at a high concentration of thiosulfate, an energy source, without growth inhibition by the excessively high ionic strength and thiosulfate itself. CO2 was supplied by saturating the medium with a 1 atm CO2 gas or a gaseous mixture of 0.8 atm N2 and 0.2 atm CO2. The Monod equation successfully described the kinetics of CO2 fixation; the maximum specific growth rate was 0.33 h−1 regardless of CO2 pressure while the Monod constant was 0.0379 g Na2S2O3/L and 0.196 g Na2S2O3/L under 0.2 atm and 1.0 atm CO2, respectively. We found that when nutrients, including thiosulfate, were supplied sufficiently, the CO2 fixation rate at 1 atm CO2 was only slightly lower than that at 0.2 atm CO2 (e.g. only by 4.7 % for 3.0 g Na2S2O3/L). Therefore, the CO2 fixation by S. lithotrophicum 42BKTT is not subject to CO2 toxicity at least up to 1.0 atm CO2.