Transcriptome analysis of exogenous glycogen availability regulating gene expression of Streptococcus suis

Abstract:

[Background] Carbohydrate is closely related to the colonization and pathogenicity of Streptococcus suis in hosts, and the glycogen released from host cells may be an important carbon source of S. suis. [Objective] This paper aims to analyze the effect of exogenous glycogen on the transcriptome response of S. suis, especially the virulence genes. [Methods] The virulent S. suis type 2 SC19 strain was cultured in the glycogen and glucose medium, respectively. Through high-throughput transcriptome sequencing, the effect of glycogen on the metabolic pathways and virulence genes of S. suis were identified and analyzed, followed by verification through in vitro experiment and challenge test. [Results] S. suis grew well in the medium containing glycogen as the carbon source. Transcriptome data showed 908 (46.07% of the whole genome) differentially expressed genes under the glycogen culture condition, with 501 up-regulated and 407 down-regulated. Enrichment analysis revealed that glycogen affected a wide range of basic metabolic pathways in S. suis, but the glycolysis pathway remained stable. The expression levels of 30 virulence genes significantly changed. In particular, a series of known and important virulence factors, such as SLY, ApuA, and ArcABC, were highly up-regulated (fold change>20). Moreover, results showed that the hemolytic activity, adhesion, and invasion of S. suis cultured in glycogen significantly enhanced, and that its virulence to the tested animal model predictably increased. Thus, it was confirmed that S. suis responded to glycogen and glycogen regulated the pathogenicity of S. suis. [Conclusion] Exogenous glycogen significantly affected the genome expression profile of S. suis. Such response to the carbon source suggests the adaptability of the bacteria to the changing habitats and the close relationship between the carbohydrate and S. suis pathogenicity.