Response to Gaseous NO2 Air Pollutant of P. fluorescens Airborne Strain MFAF76a and Clinical Strain MFN1032

Abstract

Human exposure to nitrogen dioxide (NO2), an air pollutant of increasing interest in biology, results in several toxic effects to human health and also to the air microbiota. The aim of this study was to investigate the bacterial response to gaseous NO2. Two Pseudomonas fluorescens strains, namely the airborne strain MFAF76a and the clinical strain MFN1032 were exposed to 0.1, 5, or 45 ppm concentrations of NO2, and their effects on bacteria were evaluated in terms of motility, biofilm formation, antibiotic resistance, as well as expression of several chosen target genes. While 0.1 and 5 ppm of NO2did not lead to any detectable modification in the studied phenotypes of the two bacteria, several alterations were observed when the bacteria were exposed to 45 ppm of gaseous NO2. We thus chose to focus on this high concentration. NO2-exposed P. fluorescens strains showed reduced swimming motility, and decreased swarming in case of the strain MFN1032. Biofilm formed by NO2-treated airborne strain MFAF76a showed increased maximum thickness compared to non-treated cells, while NO2 had no apparent effect on the clinical MFN1032 biofilm structure. It is well known that biofilm and motility are inversely regulated by intracellular c-di-GMP level. The c-di-GMP level was however not affected in response to NO2 treatment. Finally, NO2-exposed P. fluorescens strains were found to be more resistant to ciprofloxacin and chloramphenicol. Accordingly, the resistance nodulation cell division (RND) MexEF-OprN efflux pump encoding genes were highly upregulated in the two P. fluorescens strains. Noticeably, similar phenotypes had been previously observed following a NO treatment. Interestingly, an hmp-homolog gene in P. fluorescens strains MFAF76a and MFN1032 encodes a NO dioxygenase that is involved in NO detoxification into nitrites. Its expression was upregulated in response to NO2, suggesting a possible common pathway between NO and NO2 detoxification. Taken together, our study provides evidences for the bacterial response to NO2 toxicity.

Deleterious Effects of an Air Pollutant (NO2) on a Selection of Commensal Skin Bacterial Strains, Potential Contributor to Dysbiosis?

“…In P. fluorescens , no difference of swimming, swarming or twitching motility was observed with gNO 2 80 ppm, although a response delay was also noted, as previously for enzymatic activities. A different result was reported in a previous study in which 45 ppm gNO 2 were sufficient to reduce the motility of airborne and clinical strains of P. fluorescens ( Kondakova et al, 2016 ). However, it is essential to remember that P. fluorescens is a species-complex particularly wide and heterogeneous phylogenetically and physiologically and this diversity appears closely related to ecological niches ( Bodilis et al, 2004 ; Scales et al, 2014 ).…”

“…In this strain, the biofilm roughness was markedly increased suggesting a disorganization of the matrix. The effects of gNO 2 on cutaneous P. fluorescens and C. tuberculostearicum biofilm formation were limited in contrast to those observed in airborne P. fluorescens which exhibited a high increase in biofilm thickness ( Kondakova et al, 2016 ). Globally, the impact of gNO 2 on exo-enzymes production, motility, and biofilm formation suggests that gNO 2 should have limited influence on the initial steps of cutaneous bacteria implantation on skin.…”

“…The absence of impact of gNO 2 on antibiotics sensitivity of studied cutaneous bacteria suggests that gNO 2 and antibiotics act through different mechanisms. Conversely, under similar conditions of exposure, in clinical and airborne strains of P. fluorescens , gNO 2 induces an overexpression of genes encoding for the RND efflux pumps MexEF-OprN causing an increase in resistance to ciprofloxacin and chloramphenicol ( Kondakova et al, 2016 ). In fact, as observed for enzymatic activities, motility, and antibiotic susceptibility, cutaneous bacteria appear to share a common high metabolic resilience to gNO 2 .…”

The Hidden Face of Nitrogen Oxides Species: From Toxic Effects to Potential Cure?

“…More recently, an antibiotic resistance modulation was promoted by a bacterial NO 2 gaseous exposure. Indeed, an upregulation in expression of MexEF-OprN efflux pump was observed coupled with an increase in related antibiotic resistance [84]. The link between NO 2 and this efflux pump is yet not established, but the authors suggest here a potential role of this protein in the releasing of NOx outside the cells.…”

“…They also reported that the higher NO doses are used, the faster is the formation rate of NO 2 . In contrast, a direct gaseous NO 2 exposure could also be benefit in the struggle against undesirable microorganism because it seems to impact their metabolism, social behavior, and growth [84]. Moreover, a continuous high-dose NO 2 exposure seems to lead in membrane alteration through an increased permeability [98].…”