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NifA is required for maximal expression of denitrification genes in Bradyrhizobium japonicum
Author(s) -
Bueno Emilio,
Mesa Socorro,
Sanchez Cristina,
Bedmar Eulogio J.,
Delgado María J.
Publication year - 2010
Publication title -
environmental microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.954
H-Index - 188
eISSN - 1462-2920
pISSN - 1462-2912
DOI - 10.1111/j.1462-2920.2009.02076.x
Subject(s) - bradyrhizobium japonicum , nitrite reductase , biology , nitrate reductase , denitrification , mutant , biochemistry , nitrite , denitrifying bacteria , nitrate , bradyrhizobium , rpon , nitrous oxide reductase , lac operon , gene , microbiology and biotechnology , gene expression , promoter , rhizobium , rhizobiaceae , enzyme , bacteria , symbiosis , chemistry , genetics , nitrogen , ecology , organic chemistry
Summary In Bradyrhizobium japonicum the napEDABC , nirK , norCBQD and nosRZDYFLX genes, which encode reductases for nitrate, nitrite, nitric oxide and nitrous oxide, respectively, are required for denitrification. Microaerobic induction of these genes depends on fixLJ and fixK 2 , whose products form the FixLJ‐FixK 2 regulatory cascade. In B. japonicum , a second oxygen‐responsive regulatory cascade mediated by the nitrogen fixation regulatory protein, NifA, has been described. In this study, we show that disruption of nifA caused a growth defect in B. japonicum cells, when grown under denitrifying conditions, and decreased activity of periplasmic nitrate and nitrite reductase enzymes was also observed. Furthermore, expression of napE–lacZ , nirK–lacZ or norC–lacZ transcriptional fusions, as well as levels of nirK transcripts were significantly reduced in the nifA mutant after incubation under nitrate‐respiring conditions. Haem c staining analyses revealed that NifA is required for full synthesis of the NapC and NorC proteins, which are required for denitrification. A B. japonicum rpoN 1/2 mutant, lacking both copies of the gene encoding the alternative sigma factor σ 54 , was able to grow anaerobically with nitrate as terminal electron acceptor and showed wild‐type levels of nitrate and nitrite reductase activities. We propose that the nitrogen fixation regulatory protein, NifA, is involved in the maximal expression of the denitrification genes in B. japonicum . This influence is independent of σ 54 .