Heindl Jason E, Wang Yi, Heckel Brynn C, Mohari Bitan, Feirer Nathan, Fuqua Clay
Department of Biology, Indiana University, Bloomington IN, USA.
Front Plant Sci. 2014 May 6;5:176. doi: 10.3389/fpls.2014.00176. eCollection 2014.
For many pathogenic bacteria surface attachment is a required first step during host interactions. Attachment can proceed to invasion of host tissue or cells or to establishment of a multicellular bacterial community known as a biofilm. The transition from a unicellular, often motile, state to a sessile, multicellular, biofilm-associated state is one of the most important developmental decisions for bacteria. Agrobacterium tumefaciens genetically transforms plant cells by transfer and integration of a segment of plasmid-encoded transferred DNA (T-DNA) into the host genome, and has also been a valuable tool for plant geneticists. A. tumefaciens attaches to and forms a complex biofilm on a variety of biotic and abiotic substrates in vitro. Although rarely studied in situ, it is hypothesized that the biofilm state plays an important functional role in the ecology of this organism. Surface attachment, motility, and cell division are coordinated through a complex regulatory network that imparts an unexpected asymmetry to the A. tumefaciens life cycle. In this review, we describe the mechanisms by which A. tumefaciens associates with surfaces, and regulation of this process. We focus on the transition between flagellar-based motility and surface attachment, and on the composition, production, and secretion of multiple extracellular components that contribute to the biofilm matrix. Biofilm formation by A. tumefaciens is linked with virulence both mechanistically and through shared regulatory molecules. We detail our current understanding of these and other regulatory schemes, as well as the internal and external (environmental) cues mediating development of the biofilm state, including the second messenger cyclic-di-GMP, nutrient levels, and the role of the plant host in influencing attachment and biofilm formation. A. tumefaciens is an important model system contributing to our understanding of developmental transitions, bacterial cell biology, and biofilm formation.
对于许多致病细菌而言，表面附着是其与宿主相互作用过程中必需的第一步。附着之后可能会侵入宿主组织或细胞，或者形成一种称为生物膜的多细胞细菌群落。从单细胞、通常具有运动性的状态转变为固着的、多细胞的、与生物膜相关的状态，是细菌最重要的发育决策之一。根癌土壤杆菌通过将一段质粒编码的转移DNA（T-DNA）转移并整合到宿主基因组中来对植物细胞进行遗传转化，它也是植物遗传学家的一个有价值的工具。根癌土壤杆菌能在体外多种生物和非生物底物上附着并形成复杂的生物膜。尽管很少在原位进行研究，但据推测生物膜状态在该生物体的生态学中起着重要的功能作用。表面附着、运动性和细胞分裂通过一个复杂的调控网络进行协调，该网络赋予根癌土壤杆菌生命周期意想不到的不对称性。在这篇综述中，我们描述了根癌土壤杆菌与表面结合的机制以及这一过程的调控。我们重点关注基于鞭毛的运动性与表面附着之间的转变，以及有助于生物膜基质的多种细胞外成分的组成、产生和分泌。根癌土壤杆菌形成生物膜在机制上以及通过共享的调控分子与毒力相关。我们详细阐述了目前对这些及其他调控机制的理解，以及介导生物膜状态发育的内部和外部（环境）信号，包括第二信使环二鸟苷酸、营养水平，以及植物宿主在影响附着和生物膜形成中的作用。根癌土壤杆菌是一个重要的模型系统，有助于我们理解发育转变、细菌细胞生物学和生物膜形成。
