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Two-pronged survival strategy for the major cystic fibrosis pathogen, Pseudomonas aeruginosa, lacking the capacity to degrade nitric oxide during anaerobic respiration.

ABSTRACT: Protection from NO gas, a toxic byproduct of anaerobic respiration in Pseudomonas aeruginosa, is mediated by nitric oxide (NO) reductase (NOR), the norCB gene product. Nevertheless, a norCB mutant that accumulated approximately 13.6 microM NO paradoxically survived anaerobic growth. Transcription of genes encoding nitrate and nitrite reductases, the enzymes responsible for NO production, was reduced >50- and 2.5-fold in the norCB mutant. This was due, in part, to a predicted compromise of the [4Fe-4S](2+) cluster in the anaerobic regulator ANR by physiological NO levels, resulting in an inability to bind to its cognate promoter DNA sequences. Remarkably, two O(2)-dependent dioxygenases, homogentisate-1,2-dioxygenase (HmgA) and 4-hydroxyphenylpyruvate dioxygenase (Hpd), were derepressed in the norCB mutant. Electron paramagnetic resonance studies showed that HmgA and Hpd bound NO avidly, and helped protect the norCB mutant in anaerobic biofilms. These data suggest that protection of a P. aeruginosa norCB mutant against anaerobic NO toxicity occurs by both control of NO supply and reassignment of metabolic enzymes to the task of NO sequestration.

SUBMITTER: Yoon SS

PROVIDER: S-EPMC1949006 | biostudies-literature | 2007 Aug

REPOSITORIES: biostudies-literature

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Two-pronged survival strategy for the major cystic fibrosis pathogen, Pseudomonas aeruginosa, lacking the capacity to degrade nitric oxide during anaerobic respiration.

Yoon Sang Sun SS Karabulut Ahmet C AC Lipscomb John D JD Hennigan Robert F RF Lymar Sergei V SV Groce Stephanie L SL Herr Andrew B AB Howell Michael L ML Kiley Patricia J PJ Schurr Michael J MJ Gaston Benjamin B Choi Kyoung-Hee KH Schweizer Herbert P HP Hassett Daniel J DJ

The EMBO journal 20070712 15

Protection from NO gas, a toxic byproduct of anaerobic respiration in Pseudomonas aeruginosa, is mediated by nitric oxide (NO) reductase (NOR), the norCB gene product. Nevertheless, a norCB mutant that accumulated approximately 13.6 microM NO paradoxically survived anaerobic growth. Transcription of genes encoding nitrate and nitrite reductases, the enzymes responsible for NO production, was reduced >50- and 2.5-fold in the norCB mutant. This was due, in part, to a predicted compromise of the [4 ...[more]

PMID: 17627281

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Project description:Pseudomonas aeruginosa (PA) is a common bacterial pathogen, responsible for a high incidence of nosocomial and respiratory infections. KatA is the major catalase of PA that detoxifies hydrogen peroxide (H2O2), a reactive oxygen intermediate generated during aerobic respiration. Paradoxically, PA displays elevated KatA activity under anaerobic growth conditions where the substrate of KatA, H2O2, is not produced. The aim of the present study is to elucidate the mechanism underlying this phenomenon and define the role of KatA in PA during anaerobiosis using genetic, biochemical and biophysical approaches. We demonstrated that anaerobic wild-type PAO1 cells yielded higher levels of katA transcription and expression than aerobic cells, whereas a nitrite reductase mutant ?nirS produced ?50% the KatA activity of PAO1, suggesting that a basal NO level was required for the increased KatA activity. We also found that transcription of the katA gene was controlled, in part, by the master anaerobic regulator, ANR. A ?katA mutant and a mucoid mucA22 ?katA bacteria demonstrated increased sensitivity to acidified nitrite (an NO generator) in anaerobic planktonic and biofilm cultures. EPR spectra of anaerobic bacteria showed that levels of dinitrosyl iron complexes (DNIC), indicators of NO stress, were increased significantly in the ?katA mutant, and dramatically in a ?norCB mutant compared to basal levels of DNIC in PAO1 and ?nirS mutant. Expression of KatA dramatically reduced the DNIC levels in ?norCB mutant. We further revealed direct NO-KatA interactions in vitro using EPR, optical spectroscopy and X-ray crystallography. KatA has a 5-coordinate high spin ferric heme that binds NO without prior reduction of the heme iron (Kd ?6 ?M). Collectively, we conclude that KatA is expressed to protect PA against NO generated during anaerobic respiration. We proposed that such protective effects of KatA may involve buffering of free NO when potentially toxic concentrations of NO are approached.

Dataset Information

Two-pronged survival strategy for the major cystic fibrosis pathogen, Pseudomonas aeruginosa, lacking the capacity to degrade nitric oxide during anaerobic respiration.

Publications

Two-pronged survival strategy for the major cystic fibrosis pathogen, Pseudomonas aeruginosa, lacking the capacity to degrade nitric oxide during anaerobic respiration.

Similar Datasets

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