Laboratoire de Microbiologie de l'Environnement, Université de Caen, EA956 USC INRA2017 IFR 146, 14032 Caen Cedex, France.
J Bacteriol. 2010 Feb;192(3):779-85. doi: 10.1128/JB.00959-09. Epub 2009 Dec 4.
Enterococcus faecalis is equipped with two pathways of glycerol dissimilation. Glycerol can either first be phosphorylated by glycerol kinase and then oxidized by glycerol-3-phosphate oxidase (the glpK pathway) or first be oxidized by glycerol dehydrogenase and then phosphorylated by dihydroxyacetone kinase (the dhaK pathway). Both pathways lead to the formation of dihydroxyacetone phosphate, an intermediate of glycolysis. It was assumed that the glpK pathway operates during aerobiosis and that the dhaK pathway operates under anaerobic conditions. Because this had not been analyzed by a genetic study, we constructed mutants of strain JH2-2 affected in both pathways. The growth of these mutants on glycerol under aerobic and anaerobic conditions was monitored. In contrast to the former model, results strongly suggest that glycerol is catabolized simultaneously by both pathways in the E. faecalis JH2-2 strain in the presence of oxygen. In accordance with the former model, glycerol is metabolized by the dhaK pathway under anaerobic conditions. Comparison of different E. faecalis isolates revealed an impressive diversity of growth behaviors on glycerol. Analysis by BLAST searching and real-time reverse transcriptase PCR revealed that this diversity is based not on different gene contents but rather on differences in gene expression. Some strains used preferentially the glpK pathway whereas others probably exclusively the dhaK pathway under aerobic conditions. Our results demonstrate that the species E. faecalis cannot be represented by only one model of aerobic glycerol catabolism.
屎肠球菌配备了两条甘油分解途径。甘油可以先被甘油激酶磷酸化，然后被甘油-3-磷酸氧化酶氧化（glpK 途径），或者先被甘油脱氢酶氧化，然后被二羟丙酮激酶磷酸化（dhaK 途径）。这两条途径都导致了 1,3-二羟丙酮磷酸的形成，这是糖酵解的中间产物。人们认为 glpK 途径在需氧条件下起作用，而 dhaK 途径在厌氧条件下起作用。因为这一点尚未通过遗传研究进行分析，我们构建了两条途径都受影响的 JH2-2 菌株突变体。监测这些突变体在有氧和厌氧条件下利用甘油的生长情况。与之前的模型相反，结果强烈表明，在有氧气存在的情况下，E. faecalis JH2-2 菌株同时通过两条途径分解甘油。与之前的模型一致，在厌氧条件下，甘油通过 dhaK 途径代谢。对不同 E. faecalis 分离株的比较显示，它们在甘油上的生长行为存在显著的多样性。通过 BLAST 搜索和实时逆转录 PCR 分析表明，这种多样性不是基于不同的基因含量，而是基于基因表达的差异。一些菌株在需氧条件下优先使用 glpK 途径，而其他菌株可能只使用 dhaK 途径。我们的结果表明，粪肠球菌不能只用一种有氧甘油分解模型来代表。
