Department of Microbiology, 815 Biological Sciences Building, University of Georgia, Athens, GA 30602, USA.
DNA Repair (Amst). 2011 Apr 3;10(4):373-9. doi: 10.1016/j.dnarep.2011.01.004. Epub 2011 Feb 2.
Two pathways for DNA recombination, AddAB (RecBCD-like) and RecRO, were identified in Helicobacter pylori, a pathogenic bacterium that colonizes human stomachs resulting in a series of gastric diseases. In this study, we examined the physiological roles of H. pylori RecRO pathway in DNA recombinational repair. We characterized H. pylori single mutants in recR and in recO, genes in the putative gap repair recombination pathway, and an addA recO double mutant that is thus deficient in both pathways that initiate DNA recombinational repair. The recR or recO single mutants showed the same level of sensitivity to mitomycin C as the parent strain, suggesting that the RecRO pathway is not responsible for the repair of DNA double strand breaks. However, H. pylori recR and recO mutants are highly sensitive to oxidative stress and separately to acid stress, two major stress conditions that H. pylori encounters in its physiological niche. The complementation of the recR mutant restored the sensitivity to oxidative and acid stress to the wild type level. By measuring DNA transformation frequencies, the recR and recO single mutants were shown to have no effect on inter-genomic recombination, whereas the addA recO double mutant had a greatly (∼12-fold) reduced transformation frequency. On the other hand, the RecRO pathway was shown to play a significant role in intra-genomic recombination with direct repeat sequences. Whereas the recA strain had a deletion frequency 35-fold lower than that of background level, inactivation of recR resulted in a 4-fold decrease in deletion frequency. In a mouse infection model, the three mutant strains displayed a greatly reduced ability to colonize the host stomachs. The geometric means of colonization number for the wild type, recR, recO, and addA recO strains were 6 x 10⁵, 1.6 x 10⁴, 1.4 x 10⁴ and 4 x 10³ CFU/g stomach, respectively. H. pylori RecRO-mediated DNA recombinational repair (intra-genomic recombination) is thus involved in repairing DNA damage induced by oxidative and acid stresses and plays an important role in bacterial survival and persistent colonization in the host.
幽门螺杆菌（一种定植于人类胃部、可引发一系列胃部疾病的致病菌）中存在两种 DNA 重组途径：AddAB（RecBCD 样）和 RecRO。在本研究中，我们检测了幽门螺杆菌 RecRO 途径在 DNA 重组修复中的生理作用。我们对单个突变株 recR 和 recO（假定的缺口修复重组途径中的基因）以及 addA recO 双突变株（因此缺乏启动 DNA 重组修复的两种途径）进行了表征。recR 或 recO 单突变株对丝裂霉素 C 的敏感性与亲本菌株相同，这表明 RecRO 途径不负责修复 DNA 双链断裂。然而，幽门螺杆菌 recR 和 recO 突变株对氧化应激和酸应激高度敏感，这是幽门螺杆菌在生理生境中遇到的两种主要应激条件。recR 突变株的互补恢复了对氧化应激和酸应激的敏感性，使其恢复到野生型水平。通过测量 DNA 转化频率，发现 recR 和 recO 单突变株对基因组间重组没有影响，而 addA recO 双突变株的转化频率大大降低（约 12 倍）。另一方面，RecRO 途径在带有直接重复序列的基因组内重组中发挥了重要作用。recA 株的缺失频率比背景水平低 35 倍，而 recR 的失活导致缺失频率降低了 4 倍。在小鼠感染模型中，这三个突变株显示出定植宿主胃的能力大大降低。野生型、recR、recO 和 addA recO 菌株的定植数几何平均值分别为 6 x 10⁵、1.6 x 10⁴、1.4 x 10⁴和 4 x 10³ CFU/g 胃。因此，幽门螺杆菌 RecRO 介导的 DNA 重组修复（基因组内重组）参与修复氧化应激和酸应激诱导的 DNA 损伤，并在细菌存活和在宿主中持续定植中发挥重要作用。
