本文研究了在mRNA转录水平上三种L-乳酸脱氢酶基因在乳酸乳球菌KLDS4.0325不同生长阶段的表达情况。以16s rRNA作为内参基因，应用实时荧光定量PCR技术测定不同生长阶段的菌体中L-乳酸脱氢酶基因（ldh、ldhX和ldhB）表达的动态变化规律。该菌株的生长曲线呈S型，培养2~6 h为菌体的生长对数期，随后进入稳定期。生长曲线的测定表明该菌株生长力极其旺盛；16s rRNA、ldh、ldhX和ldhB基因的扩增效率曲线显示，内参基因与目的基因的扩增效率一致且接近100%，这说明利用相对荧光定量法能够较好的反应目的基因的表达量；ldh、ldhX和ldhB基因在菌体生长的3个时间点（6 h、9 h和12 h）都有一定量的表达，随着菌体的不断生长，基因表达的变化均呈现显著性上升趋势，且上升幅度不断增加，在12 h时基因表达量达到最大值。其中ldh基因在的表达量在菌体生长的3个时间点存在显著性差异，而ldhX、ldhB基因的表达量存在极显著差异。

The expressions of three L-lactate dehydrogenase genes at the mRNA transcription level during the different phases of Lactococcus lactis KLDS4.0325 growth were investigated in this study. Dynamic variations in the expressions of the three L-lactate dehydrogenase genes (ldh , ldhB, and ldhX) during the different growth phases were detected by fluorescence-based quantitative real time polymerase chain reaction (PCR), using the 16s rRNA gene as the internal standard. The growth curves of the strain were observed to be ‘S’-shaped, with the strains reaching the exponential phase of growth within 2~6 h of culture; subsequently, the cells remained in the stationary phase. The growth curve revealed the extremely strong vitality of the cells; the amplification efficiency curve of the 16s rRNA, ldh, ldhB, and ldhX genes indicated similar amplification efficiencies (close to 100%) of the reference and target genes. These results indicated that the fluorescence-based quantitative real time PCR method reflected the expression level of the target genes adequately. The ldh, ldhB, and ldhX genes were expressed to specific levels during the three time points (6 h, 9 h, and 12 h) of strain growth. In addition to the growth of the strain, the gene expression levels demonstrated a significant upward trend, with a continuous amplitude of increase; the highest expression level was observed at 12 h post-initiation. The levels of expression of the ldh gene significantly differed among the three time points; in addition, the expression of ldhB significantly differed from that of ldhX.

国家863科技计划项目（2011AA100902、2012AA022108）