Estación Experimental del Zaidin, CSIC, Granada, Spain.
J Appl Microbiol. 2013 Jun;114(6):1772-81. doi: 10.1111/jam.12168. Epub 2013 Mar 15.
In this work, phenotypic analyses of a Ensifer meliloti fixN1 mutant under free-living and symbiotic conditions have been carried out.
Ensifer meliloti fixN1 mutant showed a defect in growth as well as in TMPD-dependent oxidase activity when cells were incubated under micro-oxic conditions. Furthermore, haem c staining analyses of a fixN1 and a fixP1 mutant identified two membrane-bound c-type cytochromes of 27 and 32 kDa, present in microaerobically grown cells and in bacteroids, as the FixO and FixP components of the E. meliloti cbb3 oxidase. Under symbiotic conditions, fixN1 mutant showed a clear nitrogen fixation defect in alfalfa plants that were grown in an N-free nutrient solution during 3 weeks. However, in plants grown for a longer period, fixNOQP1 copy was not indispensable for symbiotic nitrogen fixation.
The copy 1 of the fixNOQP operon is involved in E. meliloti respiration and growth under micro-oxic conditions as well as in the expression of the FixO and FixP components of the cbb3 oxidase present in free-living microaerobic cultures and in bacteroids. This copy is important for nitrogen fixation during the early steps of the symbiosis.
It is the first time that a functional analysis of the E. meliloti copy 1 of the fixNOQP operon is performed. In this work, the cytochromes c that constitute the cbb3 oxidase operating in free-living micro-oxic cultures and in bacteroids of E. meliloti have been identified.
本工作对自由生活和共生条件下根瘤菌 fixN1 突变体的表型分析进行了研究。
根瘤菌 fixN1 突变体在微氧条件下培养时，生长和 TMPD 依赖性氧化酶活性均出现缺陷。此外，fixN1 和 fixP1 突变体的血红素 c 染色分析鉴定了两种膜结合的 c 型细胞色素，分子量分别为 27 和 32 kDa，存在于微氧生长的细胞和类菌体中，是根瘤菌 cbb3 氧化酶的 FixO 和 FixP 成分。在共生条件下，fixN1 突变体在在无氮营养溶液中生长 3 周的紫花苜蓿植物中表现出明显的固氮缺陷。然而，在生长时间更长的植物中，fixNOQP1 拷贝对于共生固氮并非必不可少。
fixNOQP 操纵子的拷贝 1 参与根瘤菌在微氧条件下的呼吸和生长，以及在自由生活的微氧培养物和类菌体中存在的 cbb3 氧化酶的 FixO 和 FixP 成分的表达。该拷贝对于共生早期的固氮作用很重要。
这是首次对根瘤菌 fixNOQP 操纵子的拷贝 1 进行功能分析。在这项工作中，鉴定了在自由生活的微氧培养物和根瘤菌类菌体中起作用的 cbb3 氧化酶的细胞色素 c。
