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Multiple transcription factors of the FNR family in denitrifying Pseudomonas stutzeri : characterization of four fnr ‐like genes, regulatory responses and cognate metabolic processes
Author(s) -
Vollack KaiUwe,
Härtig Elisabeth,
Körner Heinz,
Zumft Walter G.
Publication year - 1999
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1046/j.1365-2958.1999.01302.x
Subject(s) - biology , pseudomonas stutzeri , gene , transcription factor , genetics , denitrifying bacteria , transcription (linguistics) , cognate , microbiology and biotechnology , bacteria , denitrification , nitrogen , linguistics , philosophy , physics , quantum mechanics
Pseudomonas stutzeri is a facultative anaerobic bacterium with the capability of denitrification. In searching for regulators that control the expression of this trait in response to oxygen withdrawal, we have found an unprecedented multiplicity of four genes encoding transcription factors of the FNR family. The fnrA gene encodes a genuine FNR‐type regulator, which is expressed constitutively and controls the cytochrome cbb 3 ‐type terminal oxidase (the cco operon), cytochrome c peroxidase (the ccp gene) and the oxygen‐independent coproporphyrinogen III oxidase (the hemN gene), in addition to its previously demonstrated role in arginine catabolism (the arc operon). The fnr homologues dnrD , dnrE and dnrS encode regulators of a new subgroup within the FNR family. Their main distinctive feature is the lack of cysteine residues for complexing the [4Fe–4S] centre of redox‐active FNR‐type regulators. However, they form a phylogenetic lineage separate from the FixK branch of FNR proteins, which also lack this cysteine signature. We have studied the expression of the dnr genes under aerobic, oxygen‐limited and denitrifying conditions. DnrD is a key regulator of denitrification by selective activation of the genes for cytochrome cd 1 nitrite reductase and NO reductase. The dnrD gene is part of the 30 kb region carrying denitrification genes of P. stutzeri . Transcription of dnrD was activated in O 2 ‐limited cells and particularly strongly in denitrifying cells, but was not under the control of FnrA. In response to denitrifying growth conditions, dnrD was transcribed as part of an operon together with genes downstream and upstream of dnrD. dnrS was found about 9 kb upstream of dnrD , next to the nrdD gene for anaerobic ribonucleotide reductase. The transcription of dnrS required FnrA in O 2 ‐limited cells. Mutation of dnrS affected nrdD and the expression of ferredoxin I as an element of the oxidative stress response. The dnrE gene is part of the nar region encoding functions for respiratory nitrate reduction. We found the highest amount of dnrE transcripts in aerobically nitrate‐challenged cells. The gene was transcribed from two promoters, P1 and P2, of which promoter P1 was under the control of the nitrate response regulator NarL. The multiplicity of FNR factors in P. stutzeri underlines the versatility of the FNR scaffold to serve for transcriptional regulation directed at anaerobic or nitrate‐activated metabolic processes.