Institute for Glycomics, Griffith University, Gold Coast, Queensland 4222, Australia.
Department of Veterinary Medicine, University of Cambridge, Cambridge CB3 0ES, UK.
Nucleic Acids Res. 2023 Apr 24;51(7):3240-3260. doi: 10.1093/nar/gkad091.
Actinobacillus pleuropneumoniae is the cause of porcine pleuropneumonia, a severe respiratory tract infection that is responsible for major economic losses to the swine industry. Many host-adapted bacterial pathogens encode systems known as phasevarions (phase-variable regulons). Phasevarions result from variable expression of cytoplasmic DNA methyltransferases. Variable expression results in genome-wide methylation differences within a bacterial population, leading to altered expression of multiple genes via epigenetic mechanisms. Our examination of a diverse population of A. pleuropneumoniae strains determined that Type I and Type III DNA methyltransferases with the hallmarks of phase variation were present in this species. We demonstrate that phase variation is occurring in these methyltransferases, and show associations between particular Type III methyltransferase alleles and serovar. Using Pacific BioSciences Single-Molecule, Real-Time (SMRT) sequencing and Oxford Nanopore sequencing, we demonstrate the presence of the first ever characterised phase-variable, cytosine-specific Type III DNA methyltransferase. Phase variation of distinct Type III DNA methyltransferase in A. pleuropneumoniae results in the regulation of distinct phasevarions, and in multiple phenotypic differences relevant to pathobiology. Our characterisation of these newly described phasevarions in A. pleuropneumoniae will aid in the selection of stably expressed antigens, and direct and inform development of a rationally designed subunit vaccine against this major veterinary pathogen.
胸膜肺炎放线杆菌是猪传染性胸膜肺炎的病原体，这是一种严重的呼吸道感染，给养猪业造成了重大经济损失。许多宿主适应的细菌病原体编码称为相变异子（相位可变调节子）的系统。相变异子是由细胞质 DNA 甲基转移酶的可变表达引起的。可变表达导致细菌群体中全基因组的甲基化差异，从而通过表观遗传机制改变多个基因的表达。我们对多样化的胸膜肺炎放线杆菌菌株群体进行了检查，确定该物种存在具有相变异特征的 I 型和 III 型 DNA 甲基转移酶。我们证明了这些甲基转移酶中确实存在相变异，并且显示了特定的 III 型甲基转移酶等位基因与血清型之间的关联。使用 Pacific Biosciences 单分子实时（SMRT）测序和 Oxford Nanopore 测序，我们展示了首个经鉴定的可相变异的、胞嘧啶特异性的 III 型 DNA 甲基转移酶。胸膜肺炎放线杆菌中不同的 III 型 DNA 甲基转移酶的相变异导致了不同的相变异子的调节，以及与病理生物学相关的多种表型差异。我们对胸膜肺炎放线杆菌中这些新描述的相变异子的特性描述将有助于选择稳定表达的抗原，并指导和告知针对这种主要兽医病原体的合理设计亚单位疫苗的开发。
