The maximal rates and effective constants of 2,6-dichlorphenolindophenol and oxygen reduction by bacterim Gluconobacter oxydans in bacterial fuel cells under different conditions were evaluated. In an open-circuit mode, the rate of 2,6-dichlorphenolindophenol reduction coupled with ethanol oxidation under oxygen and nirogen atmospheres were 1.0 and 1.1 μM s–1 g–1, respectively. In closed-circuit mode, these values were 0.4 and 0.44 μM s–1 g–1, respectively. The initial rate of mediator reduction with the use of membrane fractions of bacteria in oxygen and nitrogen atmospheres in open-circuit mode were 6.3 and 6.9 μM s–1 g–1, whereas these values in closed-circuit mode comprised 2.2 and 2.4 μM s–1 g–1, respectively. The oxygen reduction rates in the presence and absence of 2,6-dichlorphenolindophenol were 0.31 and 0.32 μM s–1 g–1, respectively. The data obtained in this work demonstrated independent electron transfer from bacterial redox centers to the mediator and the absence of competition between the redox mediator and oxygen. The results can make it possible to reduce costs of microbial fuel cells based on activity of acetic acid bacteria G. oxydans.