Department of Molecular Microbiology, Utrecht University, Padualaan 8, Utrecht 3584 CH, The Netherlands.
BMC Genomics. 2013 Sep 14;14:622. doi: 10.1186/1471-2164-14-622.
Two-partner secretion systems in Gram-negative bacteria consist of an outer membrane protein TpsB that mediates the secretion of a cognate TpsA protein into the extracellular milieu. TpsA proteins have diverse, often virulence-related functions, and some of them inhibit the growth of related bacteria. In Neisseria meningitidis, several functions have been attributed to the TpsA proteins. Downstream of the tpsB and tpsA genes, several shorter tpsA-related gene cassettes, called tpsC, are located interspersed with intervening open-reading frames (IORFs). It has been suggested that the tpsC cassettes may recombine with the tpsA gene as a mechanism of antigenic variation. Here, we investigated (i) whether TpsA of N. meningitidis also has growth-inhibitory properties, (ii) whether tpsC cassettes recombine with the tpsA gene, and (iii) what the consequences of such recombination events might be.
We demonstrate that meningococcal TpsA has growth-inhibitory properties and that the IORF located immediately downstream of tpsA confers immunity to the producing strain. Although bioinformatics analysis suggests that recombination between tpsC cassettes and tpsA occurs, detailed analysis of the tpsA gene in a large collection of disease isolates of three clonal complexes revealed that the frequency is very low and cannot be a mechanism of antigenic variation. However, recombination affected growth inhibition. In vitro experiments revealed that recombination can be mediated through acquirement of tpsC cassettes from the environment and it identified the regions involved in the recombination.
Meningococcal TpsA has growth-inhibitory properties. Recombination between tpsA and tpsC cassettes occurs in vivo but is rare and has consequences for growth inhibition. A recombination model is proposed and we propose that the main goal of recombination is the collection of new IORFs for protection against a variety of TpsA proteins.
革兰氏阴性菌中的双组份分泌系统由外膜蛋白 TpsB 组成，该蛋白介导同源 TpsA 蛋白分泌到细胞外环境中。TpsA 蛋白具有多种功能，通常与毒力有关，其中一些蛋白抑制相关细菌的生长。在脑膜炎奈瑟菌中，已经确定了几种 TpsA 蛋白的功能。在 tpsB 和 tpsA 基因的下游，有几个较短的 TpsA 相关基因盒，称为 tpsC，散布在插入的开放阅读框（ORF）之间。有人提出，tpsC 盒可能与 tpsA 基因重组，作为抗原变异的一种机制。在这里，我们研究了（i）脑膜炎奈瑟菌的 TpsA 是否也具有生长抑制特性，（ii）tpsC 盒是否与 tpsA 基因重组，以及（iii）这种重组事件的后果可能是什么。
我们证明了脑膜炎奈瑟菌 TpsA 具有生长抑制特性，并且位于 tpsA 下游的 ORF 赋予了产生菌株的免疫性。尽管生物信息学分析表明 tpsC 盒与 tpsA 之间发生重组，但对三个克隆复合体的大量疾病分离株中 tpsA 基因的详细分析表明，这种重组的频率非常低，不能作为抗原变异的机制。然而，重组确实会影响生长抑制。体外实验表明，重组可以通过从环境中获得 tpsC 盒来介导，并且确定了参与重组的区域。
脑膜炎奈瑟菌 TpsA 具有生长抑制特性。tpsA 和 tpsC 盒之间的重组在体内发生，但频率很低，并且对生长抑制有影响。提出了一种重组模型，我们提出重组的主要目标是收集新的 ORF，以防止多种 TpsA 蛋白的侵害。
