| Lactobacillus delbrueckii subsp. bulgaricus is widely used in the production of fermented dairy for its excellent fermentation characteristics as a lactic acid bacteria with high economic value. Although researchers have done a lot of work on Lactobacillus delbrueckii subsp. bulgaricus, such as fermentation characteristics and application research, the metabolism mechanism has not been studied scarcely.Two-component signal system is an important regulatory mechanism involved in pH, chemiotaxis, sporulation, cell division, biofilm formation, other physiological and biochemical processes to adapt to the change of environment. The system consists of histidine kinase and response regulator protein. In recent years, researchers have found two component signal system involved in acid resistance, adherence, colonization and bacteriocin synthesis in some lactic acid bacteria.In this thesis, L. delbrueckii subsp. bulgaricus is used as sample to make functional analysis of two-component system HPK1/RR1 for revealing the role in the regulation of acid resistance and adherence. In this study, suicide vector pUC18-rr1-EM-1 and pUC18-hpk1-EM-1 were constructed and transformed into wild-type strain. The hpk1-defective mutant CH3-H1 and rr1-defective mutant CH3-R1 are screened and selected. Complementary-type strains were also constructed named as CH3-H1C and CH3-R1C. Fuctional comparative analysis of these strains were investigated, including growth rate, morphological character, acid ability, and adhesion ability. The results showed that growth rate of mutant strains was significantly lower than those of wild-type strain. The biofilm formation ability of mutant strains were lower than those of the wild-type. These results suggested that HPK1/RR1 was a pleiotropic regulatory system which could participate in acid regulation, the ability of adhesion and growth regulation. |
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