Jahid Iqbal K, Silva Anisia J, Benitez Jorge A
Morehouse School of Medicine, Department of Microbiology, Biochemistry and Immunology, 720 Westview Dr. SW, Atlanta, GA 30310-1495, USA.
Appl Environ Microbiol. 2006 Nov;72(11):7043-9. doi: 10.1128/AEM.00924-06. Epub 2006 Sep 1.
Vibrio cholerae, the causative agent of Asiatic cholera, has been reported to make large quantities of polyphosphate. Inorganic polyphosphate is a ubiquitous molecule with a variety of functions in prokaryotic and eukaryotic cells. We constructed a V. cholerae mutant with a deletion in the polyphosphate kinase (ppk) gene. The mutant was defective in polyphosphate biosynthesis. Deletion of ppk had no significant effect on production of cholera toxin, hemagglutinin/protease, motility, biofilm formation, and colonization of the suckling mouse intestine. The wild type and mutant had similar growth rates in rich and minimal medium and exhibited similar phosphate uptake and alkaline phosphatase induction. In contrast to ppk mutants from other gram-negative bacteria, the V. cholerae mutant survived prolonged starvation in LB medium and artificial seawater basal salts. The ppk mutant was significantly more sensitive to low pH, high salinity, and oxidative stress when it was cultured in low-phosphate minimal medium. The ppk mutant failed to induce catalase when it was downshifted to phosphorus-limiting conditions. Furthermore, the increased sensitivity of the ppk mutant to environmental stressors in phosphate-limited medium correlated with a diminished capacity to synthesize ATP from intracellular reservoirs. We concluded that polyphosphate protects V. cholerae from environmental stresses under phosphate limitation conditions. It has been proposed that toxigenic V. cholerae can survive in estuaries and brackish waters in which phosphorus and/or nitrogen can be a limiting nutrient. Thus, synthesis of large polyphosphate stores could enhance the ability of V. cholerae to survive in the aquatic environment.
霍乱弧菌是亚洲霍乱的病原体，据报道能产生大量多聚磷酸盐。无机多聚磷酸盐是一种普遍存在的分子，在原核细胞和真核细胞中具有多种功能。我们构建了一个多聚磷酸盐激酶（ppk）基因缺失的霍乱弧菌突变体。该突变体在多聚磷酸盐生物合成方面存在缺陷。ppk基因的缺失对霍乱毒素、血凝素/蛋白酶的产生、运动性、生物膜形成以及在乳鼠肠道中的定殖没有显著影响。野生型和突变体在丰富培养基和基本培养基中的生长速率相似，并且表现出相似的磷酸盐摄取和碱性磷酸酶诱导情况。与其他革兰氏阴性菌的ppk突变体不同，霍乱弧菌突变体在LB培养基和人工海水基础盐中能在长时间饥饿状态下存活。当在低磷酸盐基本培养基中培养时，ppk突变体对低pH、高盐度和氧化应激更为敏感。当转移到磷限制条件下时，ppk突变体无法诱导过氧化氢酶的产生。此外，ppk突变体在磷酸盐限制培养基中对环境应激源敏感性的增加与从细胞内储存库合成ATP的能力下降有关。我们得出结论，多聚磷酸盐在磷酸盐限制条件下保护霍乱弧菌免受环境压力。有人提出，产毒霍乱弧菌可以在河口和微咸水中存活，在这些环境中磷和/或氮可能是限制营养物质。因此，大量多聚磷酸盐储存的合成可以增强霍乱弧菌在水生环境中的生存能力。
