Carbon source regulates polysaccharide capsule biosynthesis in Streptococcus pneumoniae
Carbon source regulates polysaccharide capsule biosynthesis in Streptococcus pneumoniae
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DOI：
10.1074/jbc.ra119.010764
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发表时间：
2019-11-15
影响因子：
4.8
通讯作者：
Hilty, Markus
中科院分区：
文献类型：
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作者：
Troxler, Lukas J.;Werren, Joel P.;Hilty, Markus
肺炎链球菌胞外多糖膜是一种重要的毒力因子，但其调控膜厚的机制尚不完全清楚。在这里，我们研究了不同的外源碳水化合物对几种肺炎球菌血清型的包膜产量和基因表达的影响。显微镜分析表明，当肺炎链球菌生长在果糖上时，几乎没有荚膜多糖(CPS)。此外，7F型肺炎球菌在葡萄糖或蔗糖上生长时，产生的CPS比其他血清型(6B、6C、9V、15和23F)少得多。RNA测序揭示了WT菌株和6B、7F型衣壳开关突变株的不同基因对碳源的调节，但不能解释衣壳厚度调节的机制。相比之下，被囊基因敲除菌株全细胞提取物(Delta Cps)的P-31核磁共振清楚地显示了细胞在葡萄糖或果糖上生长时被膜前体代谢物的积累或缺失。这一发现表明，果糖的摄取主要导致细胞内的果糖1-磷酸，而不是转化为CPS前体。此外，7F型菌株比6B型菌株积累了更多的前体，这表明7F型菌株的前体代谢产物转化为CPS的效率较低，这与7F型菌株的被膜较薄一致。最后，同位素蔗糖标记和核磁共振分析表明，标记的果糖亚单位进入胶囊的摄取是
The exopolysaccharide capsule of Streptococcus pneumoniae is an important virulence factor, but the mechanisms that regulate capsule thickness are not fully understood. Here, we investigated the effects of various exogenously supplied carbohydrates on capsule production and gene expression in several pneumococcal serotypes. Microscopy analyses indicated a near absence of the capsular polysaccharide (CPS) when S. pneumoniae was grown on fructose. Moreover, serotype 7F pneumococci produced much less CPS than strains of other serotypes (6B, 6C, 9V, 15, and 23F) when grown on glucose or sucrose. RNA-sequencing revealed carbon source-dependent regulation of distinct genes of WT strains and capsule-switch mutants of serotypes 6B and 7F, but could not explain the mechanism of capsule thickness regulation. In contrast, P-31 NMR of whole-cell extract from capsule-knockout strains (Delta cps) clearly revealed the accumulation or absence of capsule precursor metabolites when cells were grown on glucose or fructose, respectively. This finding suggests that fructose uptake mainly results in intracellular fructose 1-phosphate, which is not converted to CPS precursors. In addition, serotype 7F strains accumulated more precursors than did 6B strains, indicating less efficient conversion of precursor metabolites into the CPS in 7F, in line with its thinner capsule. Finally, isotopologue sucrose labeling and NMR analyses revealed that the uptake of the labeled fructose subunit into the capsule is