Department of Microbiology and Immunology, School of Medicine, The University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, United States of America.
PLoS Genet. 2012;8(8):e1002877. doi: 10.1371/journal.pgen.1002877. Epub 2012 Aug 9.
Microbes have evolved many strategies to adapt to changes in environmental conditions and population structures, including cooperation and competition. One apparently competitive mechanism is contact dependent growth inhibition (CDI). Identified in Escherichia coli, CDI is mediated by Two-Partner Secretion (TPS) pathway proteins, CdiA and CdiB. Upon cell contact, the toxic C-terminus of the TpsA family member CdiA, called the CdiA-CT, inhibits the growth of CDI(-) bacteria. CDI(+) bacteria are protected from autoinhibition by an immunity protein, CdiI. Bioinformatic analyses indicate that CDI systems are widespread amongst α, β, and γ proteobacteria and that the CdiA-CTs and CdiI proteins are highly variable. CdiI proteins protect against CDI in an allele-specific manner. Here we identify predicted CDI system-encoding loci in species of Burkholderia, Ralstonia and Cupriavidus, named bcpAIOB, that are distinguished from previously-described CDI systems by gene order and the presence of a small ORF, bcpO, located 5' to the gene encoding the TpsB family member. A requirement for bcpO in function of BcpA (the TpsA family member) was demonstrated, indicating that bcpAIOB define a novel class of TPS system. Using fluorescence microscopy and flow cytometry, we show that these genes are expressed in a probabilistic manner during culture of Burkholderia thailandensis in liquid medium. The bcpAIOB genes and extracellular DNA were required for autoaggregation and adherence to an abiotic surface, suggesting that CDI is required for biofilm formation, an activity not previously attributed to CDI. By contrast to what has been observed in E. coli, the B. thailandensis bcpAIOB genes only mediated interbacterial competition on a solid surface. Competition occurred in a defined spatiotemporal manner and was abrogated by allele-specific immunity. Our data indicate that the bcpAIOB genes encode distinct classes of CDI and TPS systems that appear to function in sociomicrobiological community development.
微生物已经进化出许多策略来适应环境条件和种群结构的变化，包括合作和竞争。一种明显的竞争机制是接触依赖性生长抑制（CDI）。在大肠杆菌中发现的 CDI 是由双伙伴分泌（TPS）途径蛋白 CdiA 和 CdiB 介导的。当细胞接触时，TpsA 家族成员 CdiA 的毒性 C 端，称为 CdiA-CT，抑制 CDI(-)细菌的生长。CDI(+)细菌通过免疫蛋白 CdiI 免受自身抑制。生物信息学分析表明，CDI 系统在α、β和γ变形菌中广泛存在，并且 CdiA-CT 和 CdiI 蛋白高度可变。CdiI 蛋白以等位基因特异性的方式保护免受 CDI 的侵害。在这里，我们在伯克霍尔德氏菌、罗尔斯顿氏菌和铜绿假单胞菌的物种中鉴定出预测的 CDI 系统编码基因座，命名为 bcpAIOB，其基因顺序和存在一个小 ORF（位于编码 TpsB 家族成员的基因 5'端的 bcpO）与先前描述的 CDI 系统不同。证明了 bcpO 在 BcpA（TpsA 家族成员）功能中的必要性，表明 bcpAIOB 定义了一类新型的 TPS 系统。使用荧光显微镜和流式细胞术，我们表明这些基因在液体培养基中培养泰国伯克霍尔德氏菌时以概率方式表达。bcpAIOB 基因和细胞外 DNA 是自动聚集和附着于非生物表面所必需的，这表明 CDI 是生物膜形成所必需的，而生物膜形成以前并未归因于 CDI。与在大肠杆菌中观察到的情况不同，泰国伯克霍尔德氏菌的 bcpAIOB 基因仅在固体表面上介导细菌间竞争。竞争以特定的时空方式发生，并被等位基因特异性免疫所阻断。我们的数据表明，bcpAIOB 基因编码不同类别的 CDI 和 TPS 系统，这些系统似乎在社会微生物群落发育中发挥作用。
