关键词: 胞外多糖；嗜热链球菌；eps基因簇；基因组信息；实时聚合酶链式反应

Abstract: DNA was extracted from an exopolysaccharide (EPS)-producing strain of Streptococcus thermophilus IMAU20551, and was sequenced on an Illumina HiSeq platform and the filtrated reads were assembled using the SOAPdenovo software. Functional genes were annotated to the RAST, the Clusters of Orthologous Groups (COG), the Gene Ontology (GO), and the Kyoto Encyclopedia of Genes and Genomes (KEGG) databases. The genome of S. thermophilus IMAU20551 was found to be 1 725 107 bp in length, and 1 884 functional genes were annotated, including a complete eps gene cluster of 19 376 bp in length. In total 18 genes related to EPS synthesis were contained in the gene cluster, including epsA, epsB, epsC, epsD, epsE, eps1F, eps2F, epsJ, wzx, epsP and epsX. These genes regulate the synthesis, assembly and transport of exopolysaccharides. Furthermore, real-time PCR was used to verify the expression of the eps gene cluster from S. thermophilus IMAU20551, and it was found that all genes could be expressed. Except for a few glycosyltransferase genes, most of the genes showed maximum expression levels at 6 h. This study lays a foundation for further studies on the interaction between gene clusters and the structures of EPS from S. thermophilus.

Key words: exopolysaccharide; Streptococcus thermophilus; eps gene cluster; genomic information; real-time polymerase chain reaction