Gene Identification Of The Acid Tolerance Two-component Regulatory System HPK1/RR1

Lactobacillus delbrueckii subsp. bulgaricus is widely used in a variety of dairyproducts, which is essential for the making process of yogurt. Lactic acid bacteria willproduce lactic acid in their growth or fermentation process, resulting decreasing pH ofculture fluid or fermentation broth, suppressing the increase in the density of the cellitself. Acid capacity is essential for cell growth.After acid-induction, acid capacity of bacteria will be greatly improved and theirphysiologically will significantly change. The ability to survive in low pH of bacteriawill be improved by physiological changes. Acid tolerance response(ATR) can be bettersimulated when treated with low pH, which can cover more acid bacteria viability geneinvolved in the improved process. Therefore, expression levels of72specific genes ofmutant CH3-H, mutant CH3-R were compared with wild-type CH3after the acidinduction. The results were combined with preliminary laboratory experimental resultsunder natural fermentation to study genes activated or inhibited by HPK1/RR1.Expression of many genes of HPK1mutant CH3-H, RR1mutant CH3-R changedafter treatment with acid, compared with the wild-type strain CH3. These genesinvolved many processes including cell division and cell membrane, signal transduction,pyruvate and acetyl-CoA metabolism, lipid metabolism, transport and degradation ofpolypeptide, chaperone and proton pump and so on. Among them, signal transductionand pyruvate and acetyl-CoA metabolism changed significantly after mutantion of hpk1and rr1genes, which may possiblly affect cell growth by means of signal transducionprocesses and energy production capacity. Comparing with the normal fermentationconditions, more genes expression levels changed in the wild type strain CH3, mutantCH3-H and mutant CH3-R under acid-induction suggesting that it may be the result ofacid-induction. These results can be speculated that the acid regulation of HPK1/RR1in L. delbrueckii subsp. bulgaricus is a complex process including many metabolicpathways.cDNA-AFLP technology was used to conduct a preliminary exploration in acidregulation of L. delbrueckii subsp. bulgaricus which is of HPK1/RR1participation. Avariety of experimental conditions has been identified, so cDNA-AFLP can be carriedout to explore unknown genes associated with HPK1/RR1.