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PLoS One. 2019 Jun 3;14(6):e0216401. doi: 10.1371/journal.pone.0216401. eCollection 2019.

The anti-sigma factor MucA of Pseudomonas aeruginosa: Dramatic differences of a mucA22 vs. a ΔmucA mutant in anaerobic acidified nitrite sensitivity of planktonic and biofilm bacteria in vitro and during chronic murine lung infection.

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Department of Molecular Genetics, Biochemistry and Microbiology, University of Cincinnati College of Medicine, Cincinnati, OH United States of America.
Department of Immunology and Microbiology, University of Colorado School of Medicine, Aurora, CO United States of America.
College of Veterinary Medicine, University of Illinois at Urbana-Champaign, Urbana, IL United States of America.
Division of Biomedical Informatics, Cincinnati Children's Hospital Medical Center, Cincinnati, OH United States of America.
Department of Microbiology and Immunology, Virginia Commonwealth University Medical Center, Richmond, VA United States of America.
McGuire Veterans Affairs Medical Center, Richmond, VA United States of America.
Department of Medicine, University of Calgary, Calgary, Alberta, Canada.
Department of Medicine, Cincinnati Veterans Affairs Medical Center, Cincinnati, OH United States of America.
Pulmonary, Critical Care, and Sleep Division, Department of Medicine, University of Cincinnati College of Medicine, Cincinnati, OH United States of America.
Department of Biochemistry and Microbiology, Marshall University, Huntington, WV United States of America.
Department of Life Sciences, University of Nevada-Las Vegas, Las Vegas, NV United States of America.


Mucoid mucA22 Pseudomonas aeruginosa (PA) is an opportunistic lung pathogen of cystic fibrosis (CF) and chronic obstructive pulmonary disease (COPD) patients that is highly sensitive to acidified nitrite (A-NO2-). In this study, we first screened PA mutant strains for sensitivity or resistance to 20 mM A-NO2- under anaerobic conditions that represent the chronic stages of the aforementioned diseases. Mutants found to be sensitive to A-NO2- included PA0964 (pmpR, PQS biosynthesis), PA4455 (probable ABC transporter permease), katA (major catalase, KatA) and rhlR (quorum sensing regulator). In contrast, mutants lacking PA0450 (a putative phosphate transporter) and PA1505 (moaA2) were A-NO2- resistant. However, we were puzzled when we discovered that mucA22 mutant bacteria, a frequently isolated mucA allele in CF and to a lesser extent COPD, were more sensitive to A-NO2- than a truncated ΔmucA deletion (Δ157-194) mutant in planktonic and biofilm culture, as well as during a chronic murine lung infection. Subsequent transcriptional profiling of anaerobic, A-NO2--treated bacteria revealed restoration of near wild-type transcript levels of protective NO2- and nitric oxide (NO) reductase (nirS and norCB, respectively) in the ΔmucA mutant in contrast to extremely low levels in the A-NO2--sensitive mucA22 mutant. Proteins that were S-nitrosylated by NO derived from A-NO2- reduction in the sensitive mucA22 strain were those involved in anaerobic respiration (NirQ, NirS), pyruvate fermentation (UspK), global gene regulation (Vfr), the TCA cycle (succinate dehydrogenase, SdhB) and several double mutants were even more sensitive to A-NO2-. Bioinformatic-based data point to future studies designed to elucidate potential cellular binding partners for MucA and MucA22. Given that A-NO2- is a potentially viable treatment strategy to combat PA and other infections, this study offers novel developments as to how clinicians might better treat problematic PA infections in COPD and CF airway diseases.

Conflict of interest statement

The authors have declared that no competing interests exist.

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