Research On The Isolation, Identification, Production Characteristics And Difference Of Two-component Signal Transduction System Of Streptococcus Thermophilus

Streptococcus streptococcus is one of the most important fermentation strains in fermented dairy products such as yogurt, which has high economic value and is recognized as a probiotic, whichhas many positive effects on humen’s health.The production characteristics of S. thermophilus, such as fast growth capacity, acid production, the metabolism of lactose, the synthesis of extracellular polysaccharides(EPS), bacteriocin and flavor production, are directly related to the quality of fermented dairy. In this study, S. thermophilus strains were screened and isolated from the traditional fermented milk, and their characteristics were analyzed in order to obtain excellent strains.Two-component signal transduction system is one of the most important mechanisms when the bacteria feel the external environment signal. The purpose of this research is to establish initial connection between strains’ characteristics diversity and TCS by means of studying the distribution, the number and gene sequence information of TCS in strains. That will lay the foundation for determining the role of TCS in the production characteristics of strainsIn total 103 isolates were obtained from 26 fermented milksamples. After the elimination of poorly growing cells during subcultivations, 56 of the isolates were selected. 22 of 56 the isolates were determined to be spherical or ovoid morphology appearing as pairs or chains. After microscopic examination, physiological and biochemical tests, and 16 S rRNA identification, these strains were identified to be S. thermophilus. Two different types of 16S-23 S ITSs were observed in this study, and revealed the presence of a 16S-23 S ITS of 273 or 274 bp. Four strains, including CS2, CS9, CS15, and CS21 corresponded to ITS-St-I type. Other strains were corresponded to ITS-St-II type. In previous studies, the types of 16S-23 S ITSs were related with the some production properties, which provide reference for the follow-up experience.In this study, the important production characteristics of 22 S. thermophilus were discussed, including growth ability, acid production ability, utilization of carbohydrate, antimicrobial activity, producing flavor compounds(acetaldehyde) capability, the ability to produce extracellular polysaccharides and protease. After the comprehensive assessment, it was determined that strains CS1, CS3 andCS5 were better than others on the growth characteristics, they shownhigh growth rate, strong acid production capacity, antibacterial ability, production of extracellular polysaccharide and so on. The strains CS2 andCS9 were at a disadvantage.In this study, appropriate primers were designed based on the eight TCSs sequences information of S. thermophilu LMG18311. 22 strains DNA as templates, TCSs gene were amplified to determine the number and sequence differences of TCSs in strains. Results indicated that 22 strains contained eight TCSs, but there are different in TCSs sequences of different strains. Cluster analysis of strains was based on all TCSs sequences. All strains can be divided into two groups, strains CS2, CS9 and CS6 were belong to II group which were inferior ones, other strains were belong to I group which contained I-1, I-2, I-3 and I-4. This classification showed a certain correlation between differences characteristics of strains and TCS. The result established a foundation for further study role of TCS in difference of production characteristics of strains.