HAN Wei-wei, HOU Jun-cai, CAO Qiu-ge, GAO Meng-ni, ZHANG Jia-xiu, WU Yao, LI Xiao-jing
Lactic acid bacteria( LAB) obtain all the necessary small peptides and free amino acids through their complex proteolytic system because LAB itself can not directly use the exogenous proteins. In this study,six Lactobacillus delbrueckii subsp. bulgaricu strains( KLDS 1. 0207,1. 0501,1. 1007,1. 9201,1. 9203,1. 0208) were incubated in skim milk 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 growth curves of all incubated strains were the S-shaped growth. The proteolytic activities of the six strains incubated in skim milk were significant increase( P < 0. 01),and the genes expressions of seven target genes were unregulated with the continuous growth. The prtB and oppD gene expressions of the six strains were significantly higher in logarithmic phase than those in the control group( 4h)( P < 0. 01). The genes expressions of intracellular peptidase( pepC, pepF,pepQ,pepX,and pepT) showed significant increase at the logarithmic phase compared with the control group( P <0. 01),however the pepQ gene expression of the KLDS 1. 0207 strain was downregulated at the logarithmic phase,and unregulated in the stable phase. The results indicated that the strains with higher proteolytic activity had better growth and acidification. The key protease genes expressions of Lactobacillus debreuckii ssp. bulgaricus incubated in the skim milk were time-dependent,wherein significant differences were also observed.
