Enhancing the oxidative resistance of yoghurt starter bacteria with heterologous catalase expression in Streptococcus thermophilus

During yoghurt fermentation, the starter bacteria often suffer oxidative damage. In this study, a heme-dependent catalase gene (katE) was isolated from Lactobacillus brevis ATCC 367 and transferred into Streptococcus thermophilus ST5. The functional expression of katE in S. thermophilus ST5 resulted in enhanced oxidative stress resistance. The survival of cells in the exponential and stationary growth phases increased 52- and 143-fold, respectively, after short-term H2O2 exposure. The long-term survival rate was also significantly improved under aerobic conditions. Furthermore, the katE expression in S. thermophilus ST5 was beneficial to Lactobacillus delbrueckii subsp. bulgaricus ATCC 11842 co-cultured in milk. The survival rates of Lb. delbrueckii subsp. bulgaricus ATCC 11842 after short-term H2O2 exposure increased 18- and 127-fold during the exponential and stationary phases, respectively. The catalase expressed in S. thermophilus eliminated H2O2 efficiently, thereby protecting the yoghurt starter bacteria from oxidative damage.