Noguez Raúl, Segura Daniel, Moreno Soledad, Hernandez Alberto, Juarez Katy, Espín Guadalupe
Departamento de Microbiología Molecular, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Cuernavaca, Morelos, México.
J Mol Microbiol Biotechnol. 2008;15(4):244-54. doi: 10.1159/000108658. Epub 2007 Sep 20.
The ptsP, ptsO, and ptsN genes encode Enzyme I(Ntr), NPr, and enzyme IIA(Ntr) (IIA(Ntr)) proteins of the nitrogen-related phosphotransferase system. These proteins participate in a phosphoryl transfer chain in several bacteria, where IIA(Ntr) appears to be the terminal phosphoryl acceptor. Inactivation of the ptsP gene in Azotobacter vinelandii was previously shown to reduce poly-beta-hydroxybutyrate (PHB) production. Therefore, the question of a role of the ptsO and ptsN gene products in PHB synthesis was raised. In this work we constructed strains carrying mutations in the ptsO and ptsN genes and tested their effects on PHB accumulation. In the ptsO mutant, PHB accumulation diminished as in the ptsP mutant, while the ptsN mutant accumulated more PHB than the wild-type strain. The negative effects of the ptsP and ptsO mutations on PHB accumulation was suppressed by the ptsN mutation, and a H68A mutation in the phosphorylatable site of IIA(Ntr), impaired PHB accumulation similar to the ptsP mutation. The ptsP and ptsO mutations negatively affected transcription of the phbBAC biosynthetic operon and of the phbR gene coding for a transcriptional activator of phbBAC, whereas the ptsN mutation increased expression of this operon. Taken together our data provide genetic evidence suggesting that the non-phosphorylated form of IIA(Ntr) is involved in negative regulation of phbR and phbBAC expression in A. vinelandii.
ptsP、ptsO和ptsN基因编码与氮相关的磷酸转移酶系统的酶I（Ntr）、NPr和酶IIA（Ntr）（IIA（Ntr））蛋白。这些蛋白参与了几种细菌中的磷酸转移链，其中IIA（Ntr）似乎是末端磷酸受体。先前已证明，在棕色固氮菌中ptsP基因失活会降低聚-β-羟基丁酸酯（PHB）的产量。因此，人们提出了ptsO和ptsN基因产物在PHB合成中的作用问题。在这项工作中，我们构建了ptsO和ptsN基因发生突变的菌株，并测试了它们对PHB积累的影响。在ptsO突变体中，PHB积累如ptsP突变体一样减少，而ptsN突变体积累的PHB比野生型菌株更多。ptsP和ptsO突变对PHB积累的负面影响被ptsN突变所抑制，并且IIA（Ntr）可磷酸化位点的H68A突变损害了PHB积累，类似于ptsP突变。ptsP和ptsO突变对phbBAC生物合成操纵子以及编码phbBAC转录激活因子的phbR基因的转录产生负面影响，而ptsN突变则增加了该操纵子的表达。综合我们的数据提供了遗传证据，表明IIA（Ntr）的非磷酸化形式参与了棕色固氮菌中phbR和phbBAC表达的负调控。
