Stanley Nicola R, Lazazzera Beth A
Department of Microbiology, Immunology and Molecular Genetics, University of California, Los Angeles, Los Angeles, CA 90095, USA.
Mol Microbiol. 2005 Aug;57(4):1143-58. doi: 10.1111/j.1365-2958.2005.04746.x.
Biofilms are communities of microbial cells that are encased in a self-produced, polymeric matrix and are adherent to a surface. For several species of bacteria, an enhanced ability to form biofilms has been linked with an increased capability to produce exopolymers. To identify exopolymers of Bacillus subtilis that can contribute to biofilm formation, we transferred the genetic determinants that control exopolymer production from a wild, exopolymer-positive strain to a domesticated, exopolymer-negative strain. Mapping these genetic determinants led to the identification of gamma-poly-dl-glutamic acid (gamma-PGA) as an exopolymer that increases biofilm formation, possibly through enhancing cell-surface interactions. Production of gamma-PGA by Bacillus subtilis was known to be dependent on the two-component regulator ComPA; this study highlighted the additional dependence on the DegS-DegU, DegQ and SwrA regulator proteins. The inability of the domestic strain of B. subtilis to produce gamma-PGA was mapped to two base pairs; a single base pair change in the promoter region of degQ and a single base pair insertion in the coding region of swrA. Introduction of alleles of degQ and swrA from the wild strain into the domestic strain was sufficient to allow gamma-PGA production. In addition to controlling gamma-PGA production, ComPA and DegSU were also shown to activate biofilm formation through an as yet undefined pathway. The identification of these regulators as affecting gamma-PGA production and biofilm formation suggests that these processes are regulated by osmolarity, high cell density and phase variation.
生物膜是微生物细胞群落，这些细胞被包裹在自身产生的聚合基质中并附着于某一表面。对于几种细菌而言，形成生物膜能力的增强与产生胞外聚合物能力的提高有关。为了鉴定枯草芽孢杆菌中能够促进生物膜形成的胞外聚合物，我们将控制胞外聚合物产生的遗传决定因素从野生的、胞外聚合物阳性菌株转移到驯化的、胞外聚合物阴性菌株中。对这些遗传决定因素进行定位，从而鉴定出γ-聚-dl-谷氨酸（γ-PGA）是一种可能通过增强细胞表面相互作用来增加生物膜形成的胞外聚合物。已知枯草芽孢杆菌产生γ-PGA依赖于双组分调节因子ComPA；本研究强调了对DegS-DegU、DegQ和SwrA调节蛋白的额外依赖性。枯草芽孢杆菌驯化菌株无法产生γ-PGA的原因定位到两个碱基对；degQ启动子区域的一个单碱基对变化以及swrA编码区域的一个单碱基对插入。将野生菌株的degQ和swrA等位基因导入驯化菌株足以使其产生γ-PGA。除了控制γ-PGA的产生外，ComPA和DegSU还被证明通过一条尚未明确的途径激活生物膜形成。这些调节因子对γ-PGA产生和生物膜形成的影响表明，这些过程受渗透压、高细胞密度和相变的调节。
