Bingham-Ramos Lacey K, Hendrixson David R
University of Texas Southwestern Medical Center, Department of Microbiology, 5323 Harry Hines Boulevard, Dallas, TX 75390-9048, USA.
Infect Immun. 2008 Mar;76(3):1105-14. doi: 10.1128/IAI.01430-07. Epub 2007 Dec 17.
Campylobacter jejuni is a leading cause of bacterial gastroenteritis in humans throughout the world, but infection of animals, especially poultry, results in a commensal colonization of the intestines. We previously found that a mutant lacking docA, which encodes a putative cytochrome c peroxidase (CCP), demonstrates up to a 10(5)-fold reduction in colonization of the chick cecum compared to wild-type C. jejuni strain 81-176. Predictions from genomic sequences identified CJJ0382 as a second locus in C. jejuni encoding a CCP, making the bacterium unusual in having two putative CCPs. To understand what advantages are imparted by having two putative CCPs, we compared the colonization requirements of C. jejuni mutants lacking DocA or Cjj0382. Unlike the DeltadocA mutant, a DeltaCJJ0382 mutant demonstrates a maximal 50-fold colonization defect that is dependent on the inoculum dose. The colonization differences of mutants lacking DocA or Cjj0382 suggest that the two predicted CCPs are unlikely to perform redundant functions during in vivo growth. In the characterizations of DocA and Cjj0382, we found that they are stable periplasmic proteins with an apparent heme-dependent peroxidase activity, which are characteristics of bacterial CCPs. However, the peroxidase activities of the proteins do not appear to contribute to resistance to hydrogen peroxide. Instead, we found that resistance to hydrogen peroxide in C. jejuni is mostly attributed to the cytoplasmic catalase KatA. Our data suggest that DocA and Cjj0382 have characteristics of CCPs but likely perform different physiological functions for the bacterium in colonization that are not related to resisting oxidative stress.
空肠弯曲菌是全球人类细菌性肠胃炎的主要病因,但它感染动物,尤其是家禽后,会在肠道内形成共生定植。我们之前发现,一个缺失编码假定细胞色素c过氧化物酶(CCP)的docA基因的突变体,与野生型空肠弯曲菌81-176菌株相比,在雏鸡盲肠中的定植能力降低了多达10^5倍。基因组序列预测表明,CJJ0382是空肠弯曲菌中编码CCP的第二个位点,这使得该细菌因拥有两个假定的CCP而显得不同寻常。为了了解拥有两个假定的CCP会带来哪些优势,我们比较了缺失DocA或Cjj0382的空肠弯曲菌突变体的定植需求。与ΔdocA突变体不同,ΔCJJ0382突变体表现出最大50倍的定植缺陷,且该缺陷依赖于接种剂量。缺失DocA或Cjj0382的突变体在定植方面的差异表明,这两个预测的CCP在体内生长过程中不太可能执行冗余功能。在对DocA和Cjj0382的特性研究中,我们发现它们是稳定的周质蛋白,具有明显的血红素依赖性过氧化物酶活性,这是细菌CCP的特征。然而,这些蛋白的过氧化物酶活性似乎并未对过氧化氢抗性产生贡献。相反,我们发现空肠弯曲菌对过氧化氢的抗性主要归因于细胞质过氧化氢酶KatA。我们的数据表明,DocA和Cjj0382具有CCP的特征,但可能在细菌定植过程中执行不同的生理功能,且这些功能与抵抗氧化应激无关。