Klebsiella oxytoca M5al was used as the original strain to breed mutants after mutagenesis with NTG 44 single colony were obtained from medium containing 0.17 mol/L NaBr-NaBrO3 (proton suicide method) and 3 lactic acid-producing mutants were selected by shaking cultivation in optimized medium, their lactate dehydrogenase activity was only 50.6%, 58.8%, 61.3% of the parent strain, respectively. The lowest one of them batch-cultured in 5 L fermenter, results indicated that the yield of lactic acid of the mutant was decreased remarkably, r...