Rio Rita V M, Anderegg Matthias, Graf Joerg
Department of Molecular and Cell Biology, University of Connecticut, 91 N. Eagleville Road, Unit-3125, Storrs, CT 06269-3125, USA.
Institute for Infectious Diseases, University of Berne, Friedbühlstr. 51, CH-3010 Berne, Switzerland.
Microbiology (Reading). 2007 Jun;153(Pt 6):1897-1906. doi: 10.1099/mic.0.2006/003020-0.
The catalase gene katA of the medicinal leech symbiont Aeromonas veronii bv. sobria was cloned, sequenced, and functionally characterized. Southern hybridization, using an A. veronii katA-specific hybridization probe, suggested the presence of a single gene copy in many Aeromonas species. A. veronii katA consisted of 1446 nt encoding a protein with a high degree of similarity to the small-subunit group III bacterial catalases. A catalase-null mutant (JG186) was constructed through gene-replacement mutagenesis. In the parent strain (HM21R), catalase activity was only detected in extracts of cells grown to early exponential phase following H(2)O(2) induction, in which the ability to induce activity was inversely related to optical density. In contrast, induced JG186 cells were very sensitive to oxidative stress, with survival being affected even at low H(2)O(2) concentrations. In contrast to the findings of previous reports of other symbiotic systems, the catalase mutant was not defective in its ability to competitively colonize or persist within its host, in both co-inoculation and sole-colonization assays. This body of evidence suggests either that oxidative stress, in the form of H(2)O(2) exposure, is not encountered by the microbial partner under the examined symbiotic conditions or that compensatory mechanisms exist. The data suggest that although many colonization factors reoccur, each symbiotic system has also evolved specific mechanisms that affect symbiont-host dynamics.
对药用蚂蟥共生菌维氏气单胞菌温和生物变种（Aeromonas veronii bv. sobria）的过氧化氢酶基因katA进行了克隆、测序及功能鉴定。使用维氏气单胞菌katA特异性杂交探针进行的Southern杂交表明，许多气单胞菌物种中存在单个基因拷贝。维氏气单胞菌katA由1446个核苷酸组成，编码一种与III型小亚基细菌过氧化氢酶高度相似的蛋白质。通过基因置换诱变构建了一个过氧化氢酶缺失突变体（JG186）。在亲本菌株（HM21R）中，仅在经H₂O₂诱导生长至指数早期的细胞提取物中检测到过氧化氢酶活性，其中诱导活性的能力与光密度呈负相关。相比之下，诱导的JG186细胞对氧化应激非常敏感，即使在低H₂O₂浓度下存活率也会受到影响。与先前其他共生系统的报道结果不同，在共接种和单独定殖试验中，过氧化氢酶突变体在竞争性定殖或在宿主内持续存在的能力方面没有缺陷。这一系列证据表明，在所研究的共生条件下，微生物伙伴未遇到以H₂O₂暴露形式存在的氧化应激，或者存在补偿机制。数据表明，尽管许多定殖因子会反复出现，但每个共生系统也都进化出了影响共生体 - 宿主动态的特定机制。
