An integrated biochemical system for nitrate assimilation and nitric oxide detoxification in Bradyrhizobium japonicum.
An integrated biochemical system for nitrate assimilation and nitric oxide detoxification in Bradyrhizobium japonicum.
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DOI：
10.1042/bj20150880
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发表时间：
2016-02-01
期刊：
影响因子：
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通讯作者：
Delgado MJ
中科院分区：
文献类型：
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作者：
Cabrera JJ;Salas A;Torres MJ;Bedmar EJ;Richardson DJ;Gates AJ;Delgado MJ
我们报告了细菌硝酸盐（NO3−）同化和一氧化氮（NO）解毒的双功能系统。同化NO3−还原酶（NasC）可以产生一氧化氮（NO）。NO解毒系统的共表达可以在厌氧NO3−依赖性生长过程中抵消细胞毒性NO的积累。根瘤菌被认为与豆科植物建立固氮共生相互作用。大豆的共生体大豆慢生根瘤菌（Bradyrhizobium japonicum）可以在以硝酸盐（NO3−）或亚硝酸盐（NO2−）作为唯一氮源的自由生活条件下繁殖和生长。与同化NO3−的相关细菌不同，B中编码同化NO3−还原酶（nasC）和NO2−还原酶（nirA）的基因。japonicum位于不同的染色体位点。nasC基因与编码ABC型NO3−转运蛋白、主要促进剂家族NO3−/NO2−转运蛋白（NarK）、黄素蛋白（Flp）和单域血红蛋白（Bjgb）的基因一起定位。然而，nirA与NO3−/NO2−反应调节因子（NasS-NasT）的基因簇在一起。在本研究中，我们证明了NasC和NirA都是NO3−同化的关键，并且NO3−而不是NO2−的生长需要flp，这意味着Flp可能作为NasC的电子供体。此外，bjgb和flp编码一氧化氮（NO）解毒系统，其功能是减轻作为NO3−同化的副产物形成的细胞毒性NO。进一步的实验表明，narK-bjgb-flp-nasC转录单位和nirA基因的NO3-响应性表达需要NasT，并且NasS也参与了这种新型的二分同化NO3-/NO2-还原酶途径的调控。
We report a dual functional system for bacterial nitrate (NO3−) assimilation and nitric oxide (NO) detoxification. The assimilatory NO3− reductase (NasC) can generate nitric oxide (NO). Co-expression of an NO-detoxification system acts to counteract accumulation of cytotoxic NO during anaerobic NO3−-dependent growth. Rhizobia are recognized to establish N2-fixing symbiotic interactions with legume plants. Bradyrhizobium japonicum, the symbiont of soybeans, can denitrify and grow under free-living conditions with nitrate (NO3−) or nitrite (NO2−) as sole nitrogen source. Unlike related bacteria that assimilate NO3−, genes encoding the assimilatory NO3− reductase (nasC) and NO2− reductase (nirA) in B. japonicum are located at distinct chromosomal loci. The nasC gene is located with genes encoding an ABC-type NO3− transporter, a major facilitator family NO3−/NO2− transporter (NarK), flavoprotein (Flp) and single-domain haemoglobin (termed Bjgb). However, nirA clusters with genes for a NO3−/NO2−-responsive regulator (NasS-NasT). In the present study, we demonstrate NasC and NirA are both key for NO3− assimilation and that growth with NO3−, but not NO2− requires flp, implying Flp may function as electron donor to NasC. In addition, bjgb and flp encode a nitric oxide (NO) detoxification system that functions to mitigate cytotoxic NO formed as a by-product of NO3− assimilation. Additional experiments reveal NasT is required for NO3−-responsive expression of the narK-bjgb-flp-nasC transcriptional unit and the nirA gene and that NasS is also involved in the regulatory control of this novel bipartite assimilatory NO3−/NO2− reductase pathway.