Campos Evangelina, de la Riva Lucia, Garces Fernando, Giménez Rosa, Aguilar Juan, Baldoma Laura, Badia Josefa
Department of Biochemistry and Molecular Biology, Institut de Biomedecina de la Universitat de Barcelona, Faculty of Pharmacy, University of Barcelona, Barcelona, Spain.
J Bacteriol. 2008 Oct;190(20):6615-24. doi: 10.1128/JB.00815-08. Epub 2008 Aug 15.
The capacity to both ferment and oxidize L-ascorbate has been widely documented for a number of enteric bacteria. Here we present evidence that all the strains of Klebsiella pneumoniae tested in this study ferment L-ascorbate using the ula regulon-encoded proteins. Under aerobic conditions, several phenotypes were observed for the strains. Our results showed that the yiaK-S system is required for this aerobic metabolic process. Gel shift experiments performed with UlaR and YiaJ and probes corresponding to the specific promoters indicated that L-ascorbate-6-phosphate is the effector molecule recognized by both regulators, since binding of the repressors to their recognition sites was impaired by the presence of this compound. We demonstrated that in K. pneumoniae cells L-ascorbate-6-phosphate is formed only by the action of the UlaABC phosphotransferase system. This finding explains why strains that lack the ula genetic system and therefore are unable to form the inducer intracellularly cannot efficiently use this vitamin as a carbon source under either anaerobic or aerobic conditions. Thus, efficient aerobic metabolism of L-ascorbate in K. pneumoniae is dependent on the presence of both the yiaK-S and ula systems. The expression of the yiaK-S operon, but not the expression of the ula regulon, is controlled by oxygen availability. Both systems are regulated by the cyclic AMP (cAMP)-cAMP receptor protein (CRP) complex and by IHF.
许多肠道细菌都具有发酵和氧化L-抗坏血酸的能力，这已得到广泛记载。在此，我们提供证据表明，本研究中测试的所有肺炎克雷伯菌菌株都利用ula操纵子编码的蛋白质发酵L-抗坏血酸。在有氧条件下，观察到这些菌株有几种表型。我们的结果表明，yiaK-S系统是这种有氧代谢过程所必需的。用UlaR和YiaJ以及对应于特定启动子的探针进行的凝胶迁移实验表明，6-磷酸-L-抗坏血酸是这两种调节因子识别的效应分子，因为该化合物的存在会损害阻遏物与其识别位点的结合。我们证明，在肺炎克雷伯菌细胞中，6-磷酸-L-抗坏血酸仅由UlaABC磷酸转移酶系统的作用形成。这一发现解释了为什么缺乏ula遗传系统因而无法在细胞内形成诱导物的菌株，在厌氧或有氧条件下都不能有效地将这种维生素用作碳源。因此，肺炎克雷伯菌中L-抗坏血酸的有效有氧代谢依赖于yiaK-S和ula系统的存在。yiaK-S操纵子的表达，而不是ula操纵子的表达，受氧气可用性的控制。这两个系统都受环腺苷酸（cAMP）-cAMP受体蛋白（CRP）复合物和整合宿主因子（IHF）的调节。
