Batut J, Boistard P
Laboratoire de Biologie Moléculaire des Relations Plantes-Microorganismes, CNRS INRA, Castanet-Tolosan, France.
Antonie Van Leeuwenhoek. 1994;66(1-3):129-50. doi: 10.1007/BF00871636.
Rhizobia are gram-negative bacteria with two distinct habitats: the soil rhizosphere in which they have a saprophytic and, usually, aerobic life and a plant ecological niche, the legume nodule, which constitutes a microoxic environment compatible with the operation of the nitrogen reducing enzyme nitrogenase. The purpose of this review is to summarize the present knowledge of the changes induced in these bacteria when shifting to a microoxic environment. Oxygen concentration regulates the expression of two major metabolic pathways: energy conservation by respiratory chains and nitrogen fixation. After reviewing the genetic data on these metabolic pathways and their response to oxygen we will put special emphasis on the regulatory molecules which are involved in the control of gene expression. We will show that, although homologous regulatory molecules allow response to oxygen in different species, they are assembled in various combinations resulting in a variable regulatory coupling between genes for microaerobic respiration and nitrogen fixation genes. The significance of coordinated regulation of genes not essential for nitrogen fixation with nitrogen fixation genes will also be discussed.
根瘤菌是革兰氏阴性菌，有两个不同的生存环境：土壤根际，它们在其中过着腐生且通常为需氧的生活；以及植物生态位，即豆科植物根瘤，它构成了一个与固氮酶（一种能还原氮的酶）发挥作用相适应的微氧环境。本综述的目的是总结目前关于这些细菌在转变至微氧环境时所发生变化的知识。氧气浓度调节两条主要代谢途径的表达：通过呼吸链进行能量守恒以及固氮作用。在回顾了关于这些代谢途径及其对氧气反应的遗传数据后，我们将特别强调参与基因表达调控的调节分子。我们将表明，尽管同源调节分子使不同物种能够对氧气作出反应，但它们以各种组合方式组装，导致微需氧呼吸基因与固氮基因之间的调控偶联存在差异。同时也将讨论对固氮并非必需的基因与固氮基因协同调控的意义。
