Lactic acid bacteria (LAB) obtain all the necessary small peptides and free amino acids by their complex proteolytic system,because LAB itself can not directly use the exogenous proteins.In this study,six Lactobadllus bulgaricu strains (KLDS 1.0207,1.0501,1.1007,1.9201,1.9203,and 1.0208) which had different initial pH values(5.6,5.9,6.2,6.5) incubated in skim milk were to analyze the dynamic changes of the genes expressions of the key proteinase (prtB,oppD,pepC,pepF,pepQ,pepX and pepT) at the mRNA transcription level using the real-time quantitative PCR technique.The effects of initial pH on key proteolytic enzyme genes expression among the six strains was significant (P＜0.05),it was up-regulated that the genes expression of the key proteolytic enzyme for the strains KLDS 1.0501,1.9201,1.9203 and 1.0208 with the increase of initial pH in skim milk.Meanwhile,some genes increased continuously at the initial pH6.5,significant differences in which are also observed.%由于保加利亚乳杆菌自身不能直接利用外源蛋白,其必须通过蛋白水解体系外源蛋白质,生成供菌体正常生长需要的短肽和游离氨基酸.选择具有高蛋白水解活力的6株保加利亚乳杆菌作为供试菌种.将菌株接种于不同初始pH值的灭菌脱脂乳中,在mRNA转录水平上,应用实时荧光定量PCR技术,探讨保加利亚乳杆菌的蛋白水解体系中关键蛋白酶基因表达情况.结果表明:在脱脂乳体系中,初始pH值对保加利亚乳杆菌蛋白水解关键酶基因的表达存在显著影响,随着初始pH值的升高菌株KLDS 1.0501,1.9201,1.9203和1.0208的各基因表达量均上调,在pH=6.5时,部分基因表达量继续上调,且各菌株间蛋白基因表达有较大差异.
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