Great Lakes Bioenergy Research Center, University of Wisconsin-Madison, Madison, WI, USA.
BMC Microbiol. 2013 Jun 12;13:130. doi: 10.1186/1471-2180-13-130.
Many pathogenic E. coli strains secrete virulence factors using type II secretory systems, homologs of which are widespread in Gram-negative bacteria. Recently, the enteropathogenic Escherichia coli strain E2348/69 was shown to secrete and surface-anchor SslE, a biofilm-promoting virulence factor, via a type II secretion system. Genes encoding SslE and its associated secretion system are conserved in some non-pathogenic E. coli, including the commonly-used W (Waksman) strain.
We report here that E. coli W uses its type II secretion system to export a cognate SslE protein. SslE secretion is temperature- and nutrient-dependent, being robust at 37°C in rich medium but strongly repressed by lower temperatures or nutrient limitation. Fusing either of two glycosyl hydrolases to the C-terminus of SslE prevented it from being secreted or surface-exposed. We screened mutations that inactivated the type II secretion system for stress-related phenotypes and found that inactivation of the secretion system conferred a modest increase in tolerance to high concentrations of urea. Additionally, we note that the genes encoding this secretion system are present at a hypervariable locus and have been independently lost or gained in different lineages of E. coli.
The non-pathogenic E. coli W strain shares the extracellular virulence factor SslE, and its associated secretory system, with pathogenic E. coli strains. The pattern of regulation of SslE secretion we observed suggests that SslE plays a role in colonization of mammalian hosts by non-pathogenic as well as pathogenic E. coli. Our work provides a non-pathogenic model system for the study of SslE secretion, and informs future research into the function of SslE during host colonization.
许多致病性大肠杆菌菌株通过 II 型分泌系统分泌毒力因子，该系统在革兰氏阴性菌中广泛存在。最近，肠致病性大肠杆菌菌株 E2348/69 被证明通过 II 型分泌系统分泌和表面锚定生物膜促进毒力因子 SslE。编码 SslE 及其相关分泌系统的基因在一些非致病性大肠杆菌中保守，包括常用的 W（Waksman）菌株。
我们在这里报告，大肠杆菌 W 使用其 II 型分泌系统来输出同源的 SslE 蛋白。SslE 分泌受温度和营养依赖性影响，在富含营养的培养基中 37°C 时强劲，但在较低温度或营养限制下强烈受到抑制。将两个糖基水解酶中的任何一个融合到 SslE 的 C 末端都可以防止其分泌或表面暴露。我们筛选了使 II 型分泌系统失活的突变体，以寻找与应激相关的表型，并发现该分泌系统的失活赋予了对高浓度尿素的适度耐受性增加。此外，我们注意到编码该分泌系统的基因存在于高变区位点，并且在不同大肠杆菌谱系中已独立丢失或获得。
非致病性大肠杆菌 W 株与致病性大肠杆菌株共享细胞外毒力因子 SslE 和其相关分泌系统。我们观察到的 SslE 分泌调节模式表明，SslE 在非致病性和致病性大肠杆菌对哺乳动物宿主的定植中发挥作用。我们的工作为 SslE 分泌的研究提供了非致病性模型系统，并为未来宿主定植期间 SslE 功能的研究提供了信息。
