Evaluation of nitric oxide production by lactobacilli

Six strains of Lactobacillus fermentum and Lactobacillus plantarum were inv estigated for nitric oxide (NO) production. First, the potential presence o f NO synthase was examined. None of the strains of L. fermentum and L. plan tarum examined produced NO from L-arginine under aerobic conditions. Intere stingly, all L. fermentum strains expressed strong L-arginine deiminase act ivity. All L. fermentum strains produced NO in MRS broth, but the NO was fo und to be chemically derived from nitrite, which was produced by L. ferment um from nitrate present in the medium. Indeed all L. fermentum strains expr ess nitrate reductase under anaerobic conditions. Moreover, one strain, L. fermentum LF1, had nitrate reductase activity under aerobic conditions. It was also found that L. fermentum strains JCM1173 and LF I possessed ammonif ying nitrite reductase. The latter strain also had denitrifying nitrite red uctase activity at neutral pH under both anaerobic and aerobic conditions. The LF1 strain is thus capable of biochemically converting nitrate to NO. N O and nitrite produced from nitrate by lactobacilli may constitute a potent ial antimicrobial mechanism.