The latency phase, growth rate, cell yield and end-products of Lactobacillus sanfranciscensis CB1 were affected by oxygen and the supply of 225 microM Mn2+. Mn2+ was especially related to the highest substrate consumption. Aerobiosis and Mn2+ supply were responsible for the highest superoxide dismutase activity. An auto-inhibitory accumulation of H2O2 meant that the survival of air-grown cells supplied with Mn2+ rapidly decreased during the stationary phase. As shown by sodium dodecyl sulfate/polyacrylamide gel electrophoresis, Mn2+ supply influenced protein expression. As shown by non-denaturating zymograms, Lb. sanfranciscensis CB1 expressed an approximately 12.5-kDa superoxide dismutase, which is probably Mn-dependent. The enzyme was insensitive to H2O2 treatment, was not induced by the presence of paraquat under aerobic conditions and was relatively stable at pH 4.0. Sourdoughs that contained high levels of oxygen enhanced cell growth, acidification and acetic acid production by Lb. sanfranciscensis CB1.