Dependence of the specific growth rate of methanogenic mutualistic cocultures on the methanogen

Methanogenesis from ethanol was studied in batch cocultures of a proton-reducing acetogenic Desulfovibrio sp. together with one of eight methanogenic bacteria representing five genera. A mathematical model of mutualistic cocultures predicts an equalisation in the specific growth rates of the two species which defines a specific growth rate for the coculture. At non-limiting ethanol concentrations the model predicts that the specific growth rate of the coculture is dependent upon the K_s (H₂) of the methanogen and its maximum specific growth rate in axenic culture when utilising H₂ as the energy source. We demonstrate experimentally that with methanogens known to have similar K_s (H₂) values, the specific growth rates of methanogenic mutualistic cocultures are dependent upon the maximum specific growth rates of the methanogens.