期刊
JOURNAL OF INDUSTRIAL MICROBIOLOGY & BIOTECHNOLOGY
卷 46, 期 5, 页码 751-758出版社
SPRINGER HEIDELBERG
DOI: 10.1007/s10295-019-02145-x
关键词
gal operon; Galactose positive; galK promoter; Streptococcus thermophilus
资金
- National Natural Science Foundation of China [31871776, 31771956]
- National Key R&D Program of China [2018YFD0502306]
- Natural Science Foundation of Shanghai [18ZR1426800]
- Guangdong Sci. Tech project [2014B020201001, 2017A030313149]
- Nansha District Sci. Tech project [2015GG003]
- Shuguang Program by Shanghai Education Development Foundation [15SG42]
- Shanghai Municipal Education Commission [15SG42]
Streptococcus thermophilus is one of the most important homo-fermentative thermophilic bacteria, which is widely used as a starter culture in dairy industry. Both wild-type galactose-negative (Gal(-)) S. thermophilus AR333 and galactose-positive (Gal(+)) S. thermophilus S-3 in this study were isolated from Chinese traditional dairy products. Here, to access the mechanism of the difference of galactose utilization between strains AR333 and S-3, the expression of gal-lac operons was examined using real-time qPCR in the presence of different sugars, and the gene organization of gal-lac operons was characterized using comparative genomics analysis. As compared with medium containing glucose, the expression of gal-lac operons in AR333 and S-3 was significantly activated (>5-fold) in the presence of galactose or lactose in the medium. More importantly, the expression of gal operon in S-3 was higher than that of AR333, suggesting that the strength of gal promoter in AR333 and S-3 may be different. The genomes of AR333 and S-3 were the first time sequenced to provide insight into the difference of gal-lac operons in these two strains. Comparative genomics analysis showed that gene order and individual gene size of gal-lac operons are conserved in AR333 and S-3. The DNA sequence of gal operon responsible for galactose utilization between AR333 and S-3 is almost identical except that galK promoter of S-3 possesses single base pair mutation (G to A substitution) at -9 box galK region. Moreover, the expression of red fluorescent protein can be activated by galK promoter of S-3, but cannot by galK promoter of AR333 in galactose medium, suggesting that gal operon is silent in AR333 and active in S-3 under galactose-containing medium. Overall, our results indicated that single point mutation at -9 box in the galK promoter can significantly affect the expression of gal operon and is largely responsible for the Gal(+) phenotype of S. thermophilus.
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