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Recently developed techniques involving opposed, gel-stabilized gradients of O2 and H2 S permit cultivation of a marineBeggiatoa strain as a chemolithoautotroph which uses gliding motility to precisely track the interface between H2 S and O2 . In the current study with microelectrodes, vertical profiles of H2 , O2 , and pH were measured in replicate cultures grown for various intervals. After an initial period of exponential biomass increase (doubling time, 11 h), linear growth prevailed throughout much of the time course. This H2 S-limited growth was followed by a transition to stationary phase when the declining H2 S flux was sufficient only to supply maintenance energy. During late-exponential and linear growth phases, theBeggiatoa sp. consumed a constant 0.6 mol of H2 S for each 1.0 mol of O2 , the ratio anticipated for balanced lithoautotrophic growth at the expense of complete oxidation of H2 S to SO4 2− . Over the entire range of conditions studied, this consumption ratio varied by approximately twofold. By measuring the extent to which the presence of the bacterial plate diminished the overlap of O2 and H2 S, we demonstrated that oxidation of H2 S byBeggiatoa sp. is approximately 3 orders of magnitude faster than spontaneous chemical oxidation. By integrating sulfide profiles and comparing sulfide consumed with biomass produced, a growth yield of 8.4 g (dry weight) mol−1 of H2 S was computed. This is higher than that found for sulfide-grown thiobacilli, indicating very efficient growth ofBeggiatoa sp. as a chemoautotroph. The methods used here offer a unique opportunity to determine the yield of H2 S-oxidizing chemolithoautotrophs while avoiding several problems inherent in the use of homogeneous liquid culture. Finally, by monitoring time-dependent formation of H2 S profiles under anoxic conditions, we demonstrate a method for calculating the molecular diffusion coefficient of soluble substrates in gel-stabilized media.

Growth Pattern and Yield of a Chemoautotrophic Beggiatoa sp. in Oxygen-Sulfide Microgradients