Oliveira Amanda C P, Ferreira Rafael M, Ferro Maria Inês T, Ferro Jesus A, Chandler Mick, Varani Alessandro M
School of Agricultural and Veterinarian Sciences-Agricultural and Livestock Microbiology Graduation Program, Universidade Estadual Paulista, Jaboticabal, Sao Paulo, Brazil.
School of Agricultural and Veterinarian Sciences, Universidade Estadual Paulista, Jaboticabal, Sao Paulo, Brazil.
PeerJ. 2018 Dec 19;6:e6111. doi: 10.7717/peerj.6111. eCollection 2018.
subsp. 306 (XccA) is the causal agent of type A citrus canker (CC), one of the most significant citriculture diseases. Murein lytic transglycosylases (LT), potentially involved in XccA pathogenicity, are enzymes responsible for peptidoglycan structure assembly, remodeling and degradation. They directly impact cell wall expansion during bacterial growth, septum division allowing cell separation, cell wall remodeling allowing flagellar assembly, bacterial conjugation, muropeptide recycling, and secretion system assembly, in particular the Type 3 Secretion System involved in bacterial virulence, which play a fundamental role in XccA pathogenicity. Information about the XccA LT arsenal is patchy: little is known about family diversity, their exact role or their connection to virulence in this bacterium. Among the LTs with possible involvement in virulence, two paralogue open reading frames (ORFs) (one on the chromosome and one in plasmid pXAC64) are passenger genes of the Tn family transposon Tn, known to play a significant role in the evolution and emergence of pathogenicity in and to carry a variety of virulence determinants. This study addresses LT diversity in the XccA genome and examines the role of plasmid and chromosomal Tn LT passenger genes using site-directed deletion mutagenesis and functional characterization. We identified 13 XccA LTs: 12 belong to families 1A, 1B, 1C, 1D (two copies), 1F, 1G, 3A, 3B (two copies), 5A, 6A and one which is non-categorized. The non-categorized LT is exclusive to the genus and related to the 3B family but contains an additional domain linked to carbohydrate metabolism. The categorized LTs are probably involved in cell wall remodeling to allow insertion of type 3, 4 and 6 secretion systems, flagellum assembly, division and recycling of cell wall and degradation and control of peptidoglycan production. The Tn passenger LT genes (3B family) are not essential to XccA or for CC development but are implicated in peptidoglycan metabolism, directly impacting bacterial fitness and CC symptom enhancement in susceptible hosts (e.g., ). This underlines the role of Tn as a virulence and pathogenicity-propagating agent in XccA and suggests that LT acquisition by horizontal gene transfer mediated by Tn may improve bacterial fitness, conferring adaptive advantages to the plant-pathogen interaction process.
亚种306（XccA）是A型柑橘溃疡病（CC）的病原体，柑橘溃疡病是最重要的柑橘类疾病之一。胞壁质溶解转糖基酶（LT）可能与XccA的致病性有关，是负责肽聚糖结构组装、重塑和降解的酶。它们在细菌生长过程中直接影响细胞壁扩张、允许细胞分离的隔膜分裂、允许鞭毛组装的细胞壁重塑、细菌接合、胞壁肽循环以及分泌系统组装，特别是参与细菌毒力的Ⅲ型分泌系统，这在XccA的致病性中起基本作用。关于XccA的LT库的信息不完整：关于其家族多样性、确切作用或与该细菌毒力的联系知之甚少。在可能参与毒力的LT中，两个旁系同源开放阅读框（ORF）（一个在染色体上，一个在质粒pXAC64中）是Tn家族转座子Tn的乘客基因，已知其在致病性的进化和出现中起重要作用，并携带多种毒力决定因素。本研究探讨了XccA基因组中LT的多样性，并使用定点缺失诱变和功能表征研究了质粒和染色体Tn LT乘客基因的作用。我们鉴定出13个XccA LT：12个属于1A、1B、1C、1D（两个拷贝）、1F、1G、3A、3B（两个拷贝）、5A、6A家族，还有一个未分类。未分类的LT是该属特有的，与3B家族相关，但包含一个与碳水化合物代谢相关的额外结构域。已分类的LT可能参与细胞壁重塑，以允许Ⅲ型、Ⅳ型和Ⅵ型分泌系统的插入、鞭毛组装、细胞壁的分裂和循环以及肽聚糖产生的降解和控制。Tn乘客LT基因（3B家族）对XccA或CC的发展不是必需的，但与肽聚糖代谢有关，直接影响细菌适应性并增强易感宿主（如……）中的CC症状。这强调了Tn作为XccA中毒力和致病性传播因子的作用，并表明由Tn介导的水平基因转移获得LT可能提高细菌适应性，赋予植物 - 病原体相互作用过程适应性优势。
