Cloeckaert Axel, Vergnaud Gilles, Zygmunt Michel S
INRAE, UMR ISP, Université de Tours, Nouzilly, France.
Institute for Integrative Biology of the Cell (I2BC), CEA, CNRS, Université Paris-Saclay, Gif-sur-Yvette, France.
Front Microbiol. 2020 Feb 24;11:284. doi: 10.3389/fmicb.2020.00284. eCollection 2020.
The genus comprises major pathogenic species causing disease in livestock and humans, e.g. . In the past few years, the genus has been significantly expanded by the discovery of phylogenetically more distant lineages comprising strains from diverse wildlife animal species, including amphibians and fish. The strains represent several potential new species, with as solely named representative. Being genetically more distant between each other, relative to the "classical" species, they present distinct atypical phenotypes and surface antigens. Among surface protein antigens, the Omp2a and Omp2b porins display the highest diversity in the classical species. The genes coding for these proteins are closely linked in the genome and oriented in opposite directions. They share between 85 and 100% sequence identity depending on the species, biovar, or genotype. Only the gene copy has been shown to be expressed and genetic variation is extensively generated by gene conversion between the two copies. In this study, we analyzed the loci of the non-classical spp. Starting from two distinct ancestral genes, represented by Australian rodent strains and , a stepwise nucleotide reduction was observed in the gene copy. It consisted of a first reduction affecting the region encoding the surface L5 loop of the porin, previously shown to be critical in sugar permeability, followed by a nucleotide reduction in the surface L8 loop-encoding region. It resulted in a final gene size shared between two distinct clades of non-classical spp. (African bullfrog isolates) and the group of classical species. Further evolution led to complete homogenization of both gene copies in some species such as or . The stepwise deletions seemed to be generated through recombination with the respective gene copy, presenting a conserved size among spp., and may involve short direct DNA repeats. Successive Omp2b porin alteration correlated with increasing porin permeability in the course of evolution of spp. They possibly have adapted their porin to survive environmental conditions encountered and to reach their final status as intracellular pathogen.
该属包含导致家畜和人类患病的主要致病物种，例如 。在过去几年中，通过发现系统发育上更遥远的谱系，该属得到了显著扩展，这些谱系包含来自不同野生动物物种（包括两栖动物和鱼类）的菌株。这些菌株代表了几个潜在的新物种， 是唯一命名的代表。相对于“经典” 物种，它们彼此之间在基因上距离更远，呈现出独特的非典型表型和表面抗原。在表面蛋白抗原中，Omp2a和Omp2b孔蛋白在经典 物种中表现出最高的多样性。编码这些蛋白质的基因在 基因组中紧密相连且方向相反。根据 物种、生物变种或基因型的不同，它们的序列同一性在85%至100%之间。只有 基因拷贝已被证明会表达，并且两个拷贝之间通过基因转换广泛产生遗传变异。在本研究中，我们分析了非经典 物种的 基因座。从以澳大利亚啮齿动物菌株和 代表的两个不同祖先基因开始，在 基因拷贝中观察到逐步的核苷酸减少。它首先是影响孔蛋白表面L5环编码区域的减少，该区域先前已被证明在糖通透性方面至关重要，随后是表面L8环编码区域的核苷酸减少。这导致了非经典 物种（非洲牛蛙分离株）的两个不同进化枝与经典 物种组之间最终共享的 基因大小。进一步的进化导致在一些 物种（如 或 ）中两个 基因拷贝完全同质化。逐步的 缺失似乎是通过与各自的 基因拷贝重组产生的，在 物种中呈现出保守的大小，并且可能涉及短的直接DNA重复序列。在 物种的进化过程中，连续的Omp2b孔蛋白改变与孔蛋白通透性增加相关。它们可能已经使其孔蛋白适应以在遇到的环境条件下生存，并最终成为细胞内病原体。
