The Streptococcus agalactiae Stringent Response Enhances Virulence and Persistence in Human Blood.
The Streptococcus agalactiae Stringent Response Enhances Virulence and Persistence in Human Blood.
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DOI：
10.1128/iai.00612-17
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发表时间：
2018-01
影响因子：
3.1
通讯作者：
Ratner AJ
中科院分区：
文献类型：
--
作者：
Hooven TA;Catomeris AJ;Bonakdar M;Tallon LJ;Santana-Cruz I;Ott S;Daugherty SC;Tettelin H;Ratner AJ
无乳链球菌（B组链球菌[GBS]）可导致新生儿严重感染。我们以前报道了一个转座子测序（Tn-seq）系统进行全基因组评估GBS的基因适应性。为了鉴定GBS从粘膜粘膜侵袭生活方式转变为血流侵袭所需的分子机制，我们用人全血对GBS菌株A909进行了Tn-seq。我们的分析确定了16个GBS在血液中生存的条件必需基因，其中75%是荚膜多糖（cps）操纵子的成员。在非cps基因被确定为条件必需的relA，它编码的酶的活性是中央的细菌严格的反应，一个保守的适应环境压力。我们使用靶向敲除菌株的血液共孵育研究来确认GBS缺乏包膜或严格反应激活的预期生长缺陷。出乎意料的是，我们发现relA敲除菌株表现出β-溶血素/溶细胞素的表达降低，β-溶血素/溶细胞素是促进GBS侵袭的重要细胞毒素。此外，用丝氨酸异羟肟酸盐化学活化严格响应增加β-溶血素/溶细胞素表达。为了建立严格响应导致细胞毒性增加的机制，我们对在严格响应或对照条件下生长的两种GBS菌株进行了转录组测序（RNA-seq）。这揭示了在严格响应激活过程中精氨酸脱亚胺酶途径中基因表达的保守性降低。通过与补充精氨酸和精氨酸拮抗剂刀豆氨酸共孵育，我们表明，精氨酸的可用性是GBS细胞毒性的决定因素，严格的反应激活和增加的毒力之间的途径是精氨酸依赖性。
Streptococcus agalactiae (group B Streptococcus [GBS]) causes serious infections in neonates. We previously reported a transposon sequencing (Tn-seq) system for performing genomewide assessment of gene fitness in GBS. In order to identify molecular mechanisms required for GBS to transition from a mucosal commensal lifestyle to bloodstream invasion, we performed Tn-seq on GBS strain A909 with human whole blood. Our analysis identified 16 genes conditionally essential for GBS survival in blood, of which 75% were members of the capsular polysaccharide (cps) operon. Among the non-cps genes identified as conditionally essential was relA, which encodes an enzyme whose activity is central to the bacterial stringent response—a conserved adaptation to environmental stress. We used blood coincubation studies of targeted knockout strains to confirm the expected growth defects of GBS deficient in capsule or stringent response activation. Unexpectedly, we found that the relA knockout strains demonstrated decreased expression of β-hemolysin/cytolysin, an important cytotoxin implicated in facilitating GBS invasion. Furthermore, chemical activation of the stringent response with serine hydroxamate increased β-hemolysin/cytolysin expression. To establish a mechanism by which the stringent response leads to increased cytotoxicity, we performed transcriptome sequencing (RNA-seq) on two GBS strains grown under stringent response or control conditions. This revealed a conserved decrease in the expression of genes in the arginine deiminase pathway during stringent response activation. Through coincubation with supplemental arginine and the arginine antagonist canavanine, we show that arginine availability is a determinant of GBS cytotoxicity and that the pathway between stringent response activation and increased virulence is arginine dependent.