Braun Martin, Thöny-Meyer Linda
Institut für Mikrobiologie, ETH Hönggerberg, Wolfgang-Pauli-Str. 10, 8093 Zürich, Switzerland.
J Bacteriol. 2005 Sep;187(17):5996-6004. doi: 10.1128/JB.187.17.5996-6004.2005.
Vibrio cholerae lives in different habitats, varying from aquatic ecosystems to the human intestinal tract. The organism has acquired a set of electron transport pathways for aerobic and anaerobic respiration that enable adaptation to the various environmental conditions. We have inactivated the V. cholerae ccmE gene, which is required for cytochrome c biogenesis. The resulting strain is deficient of all c-type cytochromes and allows us to characterize the physiological role of these proteins. Under aerobic conditions in rich medium, V. cholerae produces at least six c-type cytochromes, none of which is required for growth. Wild-type V. cholerae produces active fumarate reductase, trimethylamine N-oxide reductase, cbb3 oxidase, and nitrate reductase, of which only the fumarate reductase does not require maturation of c-type cytochromes. The reduction of nitrate in the medium resulted in the accumulation of nitrite, which is toxic for the cells. This suggests that V. cholerae is able to scavenge nitrate from the environment only in the presence of other nitrite-reducing organisms. The phenotypes of cytochrome c-deficient V. cholerae were used in a transposon mutagenesis screening to search for additional genes required for cytochrome c maturation. Over 55,000 mutants were analyzed for nitrate reductase and cbb3 oxidase activity. No transposon insertions other than those within the ccm genes for cytochrome c maturation and the dsbD gene, which encodes a disulphide bond reductase, were found. In addition, the role of a novel CcdA-like protein in cbb3 oxidase assembly is discussed.
霍乱弧菌生活在不同的栖息地，从水生生态系统到人类肠道。该生物体已经获得了一套用于有氧和无氧呼吸的电子传递途径，使其能够适应各种环境条件。我们已经使霍乱弧菌的ccmE基因失活，该基因是细胞色素c生物合成所必需的。产生的菌株缺乏所有c型细胞色素，这使我们能够表征这些蛋白质的生理作用。在富含营养的培养基中，在有氧条件下，霍乱弧菌至少产生六种c型细胞色素，其中没有一种是生长所必需的。野生型霍乱弧菌产生活性延胡索酸还原酶、三甲胺N-氧化物还原酶、cbb3氧化酶和硝酸盐还原酶，其中只有延胡索酸还原酶不需要c型细胞色素成熟。培养基中硝酸盐的还原导致亚硝酸盐的积累，亚硝酸盐对细胞有毒。这表明霍乱弧菌只有在存在其他亚硝酸盐还原生物体的情况下才能从环境中清除硝酸盐。细胞色素c缺陷型霍乱弧菌的表型用于转座子诱变筛选，以寻找细胞色素c成熟所需的其他基因。分析了超过55000个突变体的硝酸盐还原酶和cbb3氧化酶活性。除了细胞色素c成熟的ccm基因和编码二硫键还原酶的dsbD基因内的转座子插入外，未发现其他转座子插入。此外，还讨论了一种新型CcdA样蛋白在cbb3氧化酶组装中的作用。
