Department of Microbiology and Immunology, Stanford University School of Medicine, Stanford, California 94305, USA.
Appl Environ Microbiol. 2010 Jan;76(2):596-608. doi: 10.1128/AEM.02037-09. Epub 2009 Nov 30.
Francisella tularensis, the zoonotic cause of tularemia, can infect numerous mammals and other eukaryotes. Although studying F. tularensis pathogenesis is essential to comprehending disease, mammalian infection is just one step in the ecology of Francisella species. F. tularensis has been isolated from aquatic environments and arthropod vectors, environments in which chitin could serve as a potential carbon source and as a surface for attachment and growth. We show that F. tularensis subsp. novicida forms biofilms during the colonization of chitin surfaces. The ability of F. tularensis to persist using chitin as a sole carbon source is dependent on chitinases, since mutants lacking chiA or chiB are attenuated for chitin colonization and biofilm formation in the absence of exogenous sugar. A genetic screen for biofilm mutants identified the Sec translocon export pathway and 14 secreted proteins. We show that these genes are important for initial attachment during biofilm formation. We generated defined deletion mutants by targeting two chaperone genes (secB1 and secB2) involved in Sec-dependent secretion and four genes that encode putative secreted proteins. All of the mutants were deficient in attachment to polystyrene and chitin surfaces and for biofilm formation compared to wild-type F. novicida. In contrast, mutations in the Sec translocon and secreted factors did not affect virulence. Our data suggest that biofilm formation by F. tularensis promotes persistence on chitin surfaces. Further study of the interaction of F. tularensis with the chitin microenvironment may provide insight into the environmental survival and transmission mechanisms of this pathogen.
土拉弗朗西斯菌是土拉热的动物病原体，能感染多种哺乳动物和其他真核生物。尽管研究土拉弗朗西斯菌的发病机制对于理解疾病至关重要，但哺乳动物感染只是弗朗西斯菌属物种生态的一个环节。已经从水生环境和节肢动物媒介中分离出土拉弗朗西斯菌，在这些环境中，几丁质可以作为一种潜在的碳源，并作为附着和生长的表面。我们表明，土拉弗朗西斯菌亚种 novicida 在几丁质表面定植过程中形成生物膜。土拉弗朗西斯菌利用几丁质作为唯一碳源持续存在的能力依赖于几丁质酶，因为缺乏 chiA 或 chiB 的突变体在没有外源糖的情况下，对几丁质定植和生物膜形成的能力减弱。生物膜突变体的遗传筛选鉴定了 Sec 易位通道和 14 种分泌蛋白。我们表明，这些基因对于生物膜形成过程中的初始附着很重要。我们通过靶向参与 Sec 依赖性分泌的两个伴侣基因（secB1 和 secB2）和四个编码推定分泌蛋白的基因，生成了明确的缺失突变体。与野生型 novicida 相比，所有突变体在附着到聚苯乙烯和几丁质表面以及生物膜形成方面都存在缺陷。相比之下，Sec 易位通道和分泌因子的突变并不影响毒力。我们的数据表明，土拉弗朗西斯菌生物膜的形成促进了其在几丁质表面的持久存在。进一步研究土拉弗朗西斯菌与几丁质微环境的相互作用，可能为了解该病原体的环境生存和传播机制提供线索。
