Gauntlett Jonathan C, Nilsson Hans-Olof, Fulurija Alma, Marshall Barry J, Benghezal Mohammed
Ondek Pty Ltd and Helicobacter pylori Research Laboratory, School of Pathology and Laboratory Medicine, Marshall Centre for Infectious Disease Research and Training, University of Western Australia, Nedlands 6009, Western Australia, Australia.
Gut Pathog. 2014 Sep 5;6:35. doi: 10.1186/s13099-014-0035-z. eCollection 2014.
One mechanism utilized by bacterial pathogens for host adaptation and immune evasion is the generation of phenotypic diversity by the phasevarion that results from the differential expression of a suite of genes regulated by the activity of a phase-variable methyltransferase within a restriction modification (RM) system. Phasevarions are active in Helicobacter pylori, however there have been no studies investigating the significance of phase-variable RM systems on host colonization.
Two mutant types incapable of phase variation were constructed; a clean deletion mutant ('DEL') and a mutant ('ON') where the homopolymeric repeat was replaced with a non-repeat synonymous sequence, resulting in expression of the full-length protein. The resulting mutants were assessed for their colonisation ability in the mouse model.
Five phase-variable genes encoding either methyltransferases or members of RM systems were found in H. pylori OND79. Our mutants fell into three categories; 1, those with little effect on colonization, 2, those where expression of the full-length protein was detrimental, 3, those where both mutations were detrimental.
Our results demonstrated that phase-variable methyltransferases are critical to H. pylori colonization, suggesting that genome methylation and generation of epigenetic diversity is important for colonization and pathogenesis. The third category of mutants suggests that differential genome methylation status of H. pylori cell populations, achieved by the phasevarion, is essential for host adaptation. Studies of phase-variable RM mutants falling in the two other categories, not strictly required for colonization, represent a future perspective to investigate the role of phasevarion in persistence of H. pylori.
细菌病原体用于宿主适应和免疫逃避的一种机制是通过相变调控子产生表型多样性，相变调控子由限制修饰（RM）系统中可变甲基转移酶活性调控的一组基因的差异表达产生。相变调控子在幽门螺杆菌中具有活性，然而，尚未有研究调查可变RM系统对宿主定植的重要性。
构建了两种不能发生相变的突变体类型；一种是完全缺失突变体（“DEL”），另一种是突变体（“ON”），其中同聚物重复序列被非重复同义序列取代，导致全长蛋白表达。评估所得突变体在小鼠模型中的定植能力。
在幽门螺杆菌OND79中发现了五个编码甲基转移酶或RM系统成员的可变基因。我们的突变体分为三类；1. 对定植影响较小的；2. 全长蛋白表达有害的；3. 两种突变均有害的。
我们的结果表明，可变甲基转移酶对幽门螺杆菌的定植至关重要，这表明基因组甲基化和表观遗传多样性的产生对定植和发病机制很重要。第三类突变体表明，通过相变调控子实现的幽门螺杆菌细胞群体不同的基因组甲基化状态对宿主适应至关重要。对另外两类对定植并非严格必需的可变RM突变体的研究，代表了未来研究相变调控子在幽门螺杆菌持续性中的作用方面的展望。
