Antioxidant Defense Mechanisms in Pseudomonas aeruginosa: Role of Iron-Cofactored Superoxide Dismutase in Response to UV-C Radiations

Low-dose zinc oxide nanoparticles trigger the growth and biofilm formation of Pseudomonas aeruginosa: a hormetic response

INTRODUCTION

Hormesis describes an inverse dose-response relationship, whereby a high dose of a toxic compound is inhibitory, and a low dose is stimulatory. This study explores the hormetic response of low concentrations of zinc oxide nanoparticles (ZnO NPs) toward Pseudomonas aeruginosa.

METHOD

Samples of P. aeruginosa, i.e. the reference strain, ATCC 27,853, together with six strains recovered from patients with cystic fibrosis, were exposed to ten decreasing ZnO NPs doses (0.78-400 µg/mL). The ZnO NPs were manufactured from Peganum harmala using a chemical green synthesis approach, and their properties were verified utilizing X-ray diffraction and scanning electron microscopy. A microtiter plate technique was employed to investigate the impact of ZnO NPs on the growth, biofilm formation and metabolic activity of P. aeruginosa. Real-time polymerase chain reactions were performed to determine the effect of ZnO NPs on the expression of seven biofilm-encoding genes.

RESULT

The ZnO NPs demonstrated concentration-dependent bactericidal and antibiofilm efficiency at concentrations of 100-400 µg/mL. However, growth was significantly stimulated at ZnO NPs concentration of 25 µg/mL (ATCC 27853, Pa 3 and Pa 4) and at 12.5 µg/mL and 6.25 µg/mL (ATCC 27853, Pa 2, Pa 4 and Pa 5). No significant positive growth was detected at dilutions < 6.25 µg/mL. similarly, biofilm formation was stimulated at concentration of 12.5 µg/mL (ATCC 27853 and Pa 1) and at 6.25 µg/mL (Pa 4). At concentration of 12.5 µg/mL, ZnO NPs upregulated the expression of LasB ( ATCC 27853, Pa 1 and Pa 4) and LasR and LasI (ATCC 27853 and Pa 1) as well as RhII expression (ATCC 27853, Pa 2 and Pa 4).

CONCLUSION

When exposed to low ZnO NPs concentrations, P. aeruginosa behaves in a hormetic manner, undergoing positive growth and biofilm formation. These results highlight the importance of understanding the response of P. aeruginosa following exposure to low ZnO NPs concentrations.

Comparative proteomics unveils the bacteriostatic mechanisms of Ga(III) on the regulation of metabolic pathways in Pseudomonas aeruginosa

Gallium has a long history as a chemotherapeutic agent. The mechanisms of action of Ga(III)-based anti-infectives are different from conventional antibiotics, which primarily result from the chemical similarities of Ga(III) with Fe(III) and substitution of gallium into iron-dependent biological pathways. However, more aspects of the molecular mechanisms of Ga(III) against human pathogens, especially the effects on bacterial metabolic processes, remain to be understood. Herein, by using conventional quantitative proteomics, we identified the protein changes of Pseudomonas aeruginosa (P. aeruginosa) in response to Ga(NO3)3 treatment. We show that Ga(III) exhibits bacteriostatic mode of action against P. aeruginosa through affecting the expressions of a number of key enzymes in the main metabolic pathways, including glycolysis, TCA cycle, amino acid metabolism, and protein and nucleic acid biosynthesis. In addition, decreased expressions of proteins associated with pathogenesis and virulence of P. aeruginosa were also identified. Moreover, the correlations between protein expressions and metabolome changes in P. aeruginosa upon Ga(III) treatment were identified and discussed. Our findings thus expand the understanding on the antimicrobial mechanisms of Ga(III) that shed light on enhanced therapeutic strategies. BIOLOGICAL SIGNIFICANCE: Mounting evidence suggest that the efficacy and resistance of clinical antibiotics are closely related to the metabolic homeostasis in bacterial pathogens. Ga(III)-based compounds have been repurposed as antibacterial therapeutic candidates against antibiotics resistant pathogens, and represent a safe and promising treatment for clinical human infections, while more thorough understandings of how bacteria respond to Ga(III) treatment are needed. In the present study, we provide evidences at the proteome level that indicate Ga(III)-induced metabolic perturbations in P. aeruginosa. We identified and discussed the interference of Ga(III) on the expressions and activities of enzymes in the main metabolic pathways in P. aeruginosa. In view of our previous report that the antimicrobial efficacy of Ga(III) could be modulated according to Ga(III)-induced metabolome changes in P. aeruginosa, our current analyses may provide theoretical basis at the proteome level for the development of efficient gallium-based therapies by exploiting bacterial metabolic mechanisms.

2-Hydroxymethyl-1-methyl-5-nitroimidazole, one siderophore inhibitor, occludes quorum sensing in Pseudomonas aeruginosa

Siderophore is necessary for the survival of microorganisms and is interregulated with quorum sensing (QS) systems. It is related to growth, proliferation, virulence, and other bacterial social activities as a virulence factor. Thus, we speculated that the QS system could be occluded by inhibiting siderophore production. 2-Hydroxymethyl-1-methyl-5-nitroimidazole (HMMN), one siderophore inhibitor of Pseudomonas aeruginosa PAO1 (P. aeruginosa PAO1), was obtained by using the Chromeazurol S (CAS) method. We found that HMMN inhibited siderophore production and influenced the biological effects of QS regulation, including biofilm formation and pyocyanin production. HMMN (150 μg/ml) inhibited the siderophore production of P. aeruginosa PAO1 by 69.37%. In addition, HMMN could inhibit pyocyanin production and biofilm formation and erase the formed biofilm of P. aeruginosa PAO1. HMMN (150 μg/ml) inhibited the biofilm formation of P. aeruginosa PAO1 by 28.24%. The erasure rate of the formed biofilm reached 17.03%. Furthermore, HMMN (150 μg/ml) inhibited P. aeruginosa PAO1 pyocyanin production by 36.06%. Meanwhile, positive-control hordenine (500.0 μg/ml) reduced the biofilm formation and pyocyanin production of P. aeruginosa PAO1 by 14.42% and 34.35%, respectively. The erasure rate of hordenine to the formed biofilm is 11.05% at 500 μg/ml. Quantitative real-time polymerase chain reaction (qRT-PCR) showed that HMMN downregulates not only siderophore-related genes but also QS-related genes, as well as hordenine. These results suggest that a siderophore inhibitor could be used as a QS inhibitor to occlude the QS system and reduce virulence.

UV-C treatment inhibits browning, inactivates Pseudomonas tolaasii and reduces associated chemical and enzymatic changes of button mushrooms

BACKGROUND

Button mushrooms with completely white appearance are popular with consumers. However, button mushrooms are susceptible to infection with Pseudomonas tolaasii, which results in browning. This study evaluates the effects of ultraviolet-C (UV-C) treatment on the inactivation of P. tolaasii in vitro and in vivo and on the physiological and chemical changes of button mushrooms during storage for 21 days at 4 °C.

RESULTS

UV-C doses of 0.5 to 9.0 kJ m^-2 resulted in 3.91-6.26 log CFU mL^-1 reduction of P. tolaasii populations in vitro, and UV-C treatment reduced P. tolaasii populations inoculated on mushroom cap surfaces and browning severity. Moreover, P. tolaasii increased polyphenol oxidase (PPO) activity, and decreased phenylalanine ammonia-lyase (PAL) activity, the accumulation of phenolics and contents of brown melanin precursors, including γ-l-glutaminyl-4-hydroxybenzene (GHB), γ-l-glutaminyl-3,4-dihydroxybenzene (GDHB), and tyrosine in button mushrooms. UV-C treatment was found to reduce the negative changes due to P. tolaasii infection.

CONCLUSION

These results indicated that the application of UV-C treatment inhibited browning, inactivated P. tolaasii and reduced P. tolaasii - associated chemical and enzymatic changes of button mushrooms. © 2021 Society of Chemical Industry.

Electrochemical elimination of Microcystis aeruginosa with boron-doped diamond anode in different electrolyte systems: chemical and biological mechanisms

The chemical and biological mechanisms of electrochemical elimination of Microcystis aeruginosa (M. aeruginosa) using boron-doped diamond (BDD) anode were comparatively explored in three different electrolytes (chloride, sulfate, and phosphate solutions). The most efficient elimination of M. aeruginosa was observed in chloride solution, which was attributed to the greatest total long-lived oxidants from the favorable formation of active chlorine. Moreover, the high permeability of active chlorine resulted in profound intracellular damages to chlorophyll-a, microcystin-LR (MC-LR), superoxide dismutase (SOD) enzyme, and DNA in the chloride system. The change of membrane permeability and degradation of the released MC-LR induced by active chlorine were further confirmed by the increase of extracellular MC-LR in the initial 5 min and a complete decay in the subsequent 15 min, while the change in morphology of algae cells was insignificant from SEM images. In sulfate and phosphate electrolytes, membrane damages were much more pronounced based on lipid peroxidation observation, although changes in cell morphology was found more significant in phosphate system. The higher concentrations of oxidants (·OH, O₃, H₂O₂, S₂O₈^2-) generated in sulfate than in phosphate solution explained the greater efficiency of electrochemical elimination of M. aeruginosa in the sulfate electrolyte in terms of changes of cell density, OD₆₈₀, chlorophyll-a, MC-LR, lipids, SOD enzyme, and DNA.

Oxidative Stress Response in Pseudomonas aeruginosa

Pseudomonas aeruginosa is a Gram-negative environmental and human opportunistic pathogen highly adapted to many different environmental conditions. It can cause a wide range of serious infections, including wounds, lungs, the urinary tract, and systemic infections. The high versatility and pathogenicity of this bacterium is attributed to its genomic complexity, the expression of several virulence factors, and its intrinsic resistance to various antimicrobials. However, to thrive and establish infection, P. aeruginosa must overcome several barriers. One of these barriers is the presence of oxidizing agents (e.g., hydrogen peroxide, superoxide, and hypochlorous acid) produced by the host immune system or that are commonly used as disinfectants in a variety of different environments including hospitals. These agents damage several cellular molecules and can cause cell death. Therefore, bacteria adapt to these harsh conditions by altering gene expression and eliciting several stress responses to survive under oxidative stress. Here, we used PubMed to evaluate the current knowledge on the oxidative stress responses adopted by P. aeruginosa. We will describe the genes that are often differently expressed under oxidative stress conditions, the pathways and proteins employed to sense and respond to oxidative stress, and how these changes in gene expression influence pathogenicity and the virulence of P. aeruginosa. Understanding these responses and changes in gene expression is critical to controlling bacterial pathogenicity and developing new therapeutic agents.

Mechanisms of Bacterial Tolerance and Persistence in the Gastrointestinal and Respiratory Environments

Pathogens that infect the gastrointestinal and respiratory tracts are subjected to intense pressure due to the environmental conditions of the surroundings. This pressure has led to the development of mechanisms of bacterial tolerance or persistence which enable microorganisms to survive in these locations. In this review, we analyze the general stress response (RpoS mediated), reactive oxygen species (ROS) tolerance, energy metabolism, drug efflux pumps, SOS response, quorum sensing (QS) bacterial communication, (p)ppGpp signaling, and toxin-antitoxin (TA) systems of pathogens, such as Escherichia coli, Salmonella spp., Vibrio spp., Helicobacter spp., Campylobacter jejuni, Enterococcus spp., Shigella spp., Yersinia spp., and Clostridium difficile, all of which inhabit the gastrointestinal tract. The following respiratory tract pathogens are also considered: Staphylococcus aureus, Pseudomonas aeruginosa, Acinetobacter baumannii, Burkholderia cenocepacia, and Mycobacterium tuberculosis Knowledge of the molecular mechanisms regulating the bacterial tolerance and persistence phenotypes is essential in the fight against multiresistant pathogens, as it will enable the identification of new targets for developing innovative anti-infective treatments.