Production of a Heterologous Nonheme Catalase by Lactobacillus casei : an Efficient Tool for Removal of H 2 O 2 and Protection of Lactobacillus bulgaricus from Oxidative Stress in Milk

Abstract

ABSTRACT Lactic acid bacteria (LAB) are generally sensitive to H 2 O 2 , a compound that they can paradoxically produce themselves, as is the case for Lactobacillus bulgaricus. Lactobacillus plantarum ATCC 14431 is one of the very few LAB strains able to degrade H 2 O 2 through the action of a nonheme, manganese-dependent catalase (hereafter called MnKat). The MnKat gene was expressed in three catalase-deficient LAB species: L. bulgaricus ATCC 11842, Lactobacillus casei BL23, and Lactococcus lactis MG1363. While the protein could be detected in all heterologous hosts, enzyme activity was observed only in L. casei . This is probably due to the differences in the Mn contents of the cells, which are reportedly similar in L. plantarum and L. casei but at least 10- and 100-fold lower in Lactococcus lactis and L. bulgaricus , respectively. The expression of the MnKat gene in L. casei conferred enhanced oxidative stress resistance, as measured by an increase in the survival rate after exposure to H 2 O 2 , and improved long-term survival in aerated cultures. In mixtures of L. casei producing MnKat and L. bulgaricus , L. casei can eliminate H 2 O 2 from the culture medium, thereby protecting both L. casei and L. bulgaricus from its deleterious effects.