Enhancement of Hydrogen Peroxide Production by RNA Polymerase rif Mutations of Lactobacillus delbrueckii subsp. lactis MDC 9617

Abstract

It was found out that among rifampicin resistant mutants (Rif) of Lactobacillus delbrueckii subsp. lactis MDC 9617 the frequency of occurrence of active hydrogen peroxide producers is about five times higher than in Rif + strain. Aerobically growing Rif mutants show relatively higher kinetics of H 2 O 2 production and earlier entry into the stationary phase due to auto-inhibition caused by inhibitory concentrations of H 2 O 2 . As a result, they synthesize about the same amount of H 2 O 2 but with a smaller biomass. The concentration of H 2 O 2 , which causes auto-inhibition of aerobically growing cultures is approximately 2 times lower than the MIC of exogenous H 2 O 2 for anaerobically growing cultures. The higher sensitivity of aerobically growing cultures is rather due to the existing intracellular H 2 O 2 , which together with extracellular H 2 O 2 causes an additive/cumulative effect. Lack of auto-inhibition at 5 °C allows the mutants to accumulate 50-70% more peroxide than the parental strain. Reduction of the food-borne pathogen Escherichia coli O157:H7 by selected active Rif-4 mutant during co-cultivation in LAPTg at 5 °C was significantly higher than that of the parental strain. Due to high (~40%) co-aggregation ability of LAB with E. coli , the death of the pathogen detected at an early stage of co-cultivation in the absence of inhibitory concentrations of H 2 O 2 , may occur by direct release of H 2 O 2 onto the target cell. The ability of Rif mutants to produce higher amounts of H 2 O 2 with a smaller biomass enable them to extend the shelf-life of refrigerated food without risk of altering sensory characteristics of the latter.