Mutagenicity induced by UVC in Escherichia coli cells: reactive oxygen species involvement

Fungal Extracellular Vesicles Are Involved in Intraspecies Intracellular Communication

Fungal infections are associated with high mortality rates in humans. The risk of fungal diseases creates the urgent need to broaden the knowledge base regarding their pathophysiology. In this sense, the role of extracellular vesicles (EVs) has been described to convey biological information and participate in the fungus-host interaction process. We hypothesized that fungal EVs work as an additional element in the communication routes regulating fungal responses in intraspecies interaction systems. In this respect, the aim of this study was to address the gene regulation profiles prompted by fungal EVs in intraspecies recipient cells. Our data demonstrated the intraspecies uptake of EVs in pathogenic fungi, such as Candida albicans, Aspergillus fumigatus, and Paracoccidioides brasiliensis, and the effects triggered by EVs in fungal cells. In C. albicans, we evaluated the involvement of EVs in the yeast-to-hypha transition, while in P. brasiliensis and A. fumigatus the function of EVs as stress transducers was investigated. P. brasiliensis and A. fumigatus were exposed to an inhibitor of glycosylation or UV light, respectively. The results demonstrated the role of EVs in regulating the expression of target genes and triggering phenotypic changes. The EVs treatment induced cellular proliferation and boosted the yeast to hyphal transition in C. albicans, while they enhanced stress responsiveness in A. fumigatus and P. brasiliensis, establishing a role for EVs in fungal intraspecies communication. Thus, EVs regulate fungal behavior, acting as potent message effectors, and understanding their effects and mechanism(s) of action could be exploited in antifungal therapies. IMPORTANCE Here, we report a study about extracellular vesicles (EVs) as communication mediators in fungi. Our results demonstrated the role of EVs from Candida albicans, Aspergillus fumigatus, and Paracoccidioides brasiliensis regulating the expression of target genes and phenotypic features. We asked whether fungal EVs play a role as message effectors. We show that fungal EVs are involved in fungal interaction systems as potent message effectors, and understanding their effects and mechanisms of action could be exploited in antifungal therapies.

Contributions of Spore Secondary Metabolites to UV-C Protection and Virulence Vary in Different Aspergillus fumigatus Strains

Fungal spores contain secondary metabolites that can protect them from a multitude of abiotic and biotic stresses. Conidia (asexual spores) of the human pathogen Aspergillus fumigatus synthesize several metabolites, including melanin, which has been reported to be important for virulence in this species and to be protective against UV radiation in other fungi. Here, we investigate the role of melanin in diverse isolates of A. fumigatus and find variability in its ability to protect spores from UV-C radiation or impact virulence in a zebrafish model of invasive aspergillosis in two clinical strains and one ISS strain. Further, we assess the role of other spore metabolites in a clinical strain of A. fumigatus and identify fumiquinazoline as an additional UV-C-protective molecule but not a virulence determinant. The results show differential roles of secondary metabolites in spore protection dependent on the environmental stress and strain of A. fumigatus. As protection from elevated levels of radiation is of paramount importance for future human outer space explorations, the discovery of small molecules with radiation-protective potential may result in developing novel safety measures for astronauts.

Fungi are versatile organisms which thrive in hostile environments, including the International Space Station (ISS). Several isolates of the human pathogen Aspergillus fumigatus have been found contaminating the ISS, an environment with increased exposure to UV radiation. Secondary metabolites (SMs) in spores, such as melanins, have been shown to protect spores from UV radiation in other fungi. To test the hypothesis that melanin and other known spore SMs provide UV protection to A. fumigatus isolates, we subjected SM spore mutants to UV-C radiation. We found that 1,8-dihydroxynaphthalene (DHN)-melanin mutants of two clinical A. fumigatus strains (Af293 and CEA17) but not an ISS-isolated strain (IF1SW-F4) were more sensitive to UV-C than their respective wild-type (WT) strains. Because DHN-melanin has been shown to shield A. fumigatus from the host immune system, we examined all DHN mutants for virulence in the zebrafish model of invasive aspergillosis. Following recent studies highlighting the pathogenic variability of different A. fumigatus isolates, we found DHN-melanin to be a virulence factor in CEA17 and IF1SW-F4 but not Af293. Three additional spore metabolites were examined in Af293, where fumiquinazoline also showed UV-C-protective properties, but two other spore metabolites, monomethylsulochrin and fumigaclavine, provided no UV-C-protective properties. Virulence tests of these three SM spore mutants indicated a slight increase in virulence of the monomethylsulochrin deletion strain. Taken together, this work suggests differential roles of specific spore metabolites across Aspergillus isolates and by types of environmental stress.

Antidepressant fluoxetine induces multiple antibiotics resistance in Escherichia coli via ROS-mediated mutagenesis

BACKGROUND

Antibiotic resistance poses a great threat to global public health. Overuse of antibiotics is generally considered as the major factor contributing to it. However, little is known about whether non-antibiotic drugs could play potential roles in the emergence of antibiotic resistance.

OBJECTIVE

We aimed to investigate whether antidepressant fluoxetine induces multiple antibiotic resistances and reveal underlying mechanisms.

METHODOLOGY

Escherichia coli K12 was exposed to different concentrations of fluoxetine (0, 0.5, 5, 50 and 100 mg/L) and the resistant strains were isolated by plating on antibiotic containing plates. Resistant strains were randomly selected to determine the increase of minimum inhibition concentration (MIC) of multiple antibiotics. Genome-wide DNA sequencing was performed on cells cultured in lysogeny broth (LB) without any fluoxetine or antibiotics exposure. RNA sequencing and proteomic profiling of isolated mutants grown in LB with 100 mg/L fluoxetine were analyzed to reveal the underlying mechanisms.

RESULTS

Exposure of Escherichia coli to fluoxetine at 5-100 mg/L after repeated subculture in LB for 30 days promoted its mutation frequency resulting in increased resistance against the antibiotics chloramphenicol, amoxicillin and tetracycline. This increase was up to 5.0 × 10⁷ fold in a dose-time pattern. Isolated mutants with resistance to one of these antibiotics also exhibited multiple resistances against fluoroquinolone, aminoglycoside, β-lactams, tetracycline and chloramphenicol. According to global transcriptional and proteomic analyses, the AcrAB-TolC pump together with the YadG/YadH transporter, a Tsx channel and the MdtEF-TolC pump have been triggered to export the antibiotics to the exterior of the cell. Whole-genome DNA analysis of the mutants further revealed that ROS-mediated mutagenesis (e.g., deletion, insertion, and substitution) of DNA-binding transcriptional regulators (e.g., marR, rob, sdiA, cytR and crp) to up-regulate the expression of efflux pumps, may further enhance the antibiotic efflux.

CONCLUSIONS

Our findings for the first time demonstrated that the exposure to antidepressant fluoxetine induces multiple antibiotic resistance in E. coli via the ROS-mediated mutagenesis.

Silibinin protects Staphylococcus aureus from UVC-induced bactericide via enhanced generation of reactive oxygen species

ROS produced by silibinin suppresses UVC-inducedStaphylococcus aureuscell death.

Modification of the properties of biological membrane and its protection against oxidation by Actinidia arguta leaf extract

The aim of the study was to determine the polyphenol composition and biological activity of an extract from the leaves of kiwi. Antioxidant and hemolytic activity of the extract were examined, as well as its effect on the physical properties of the erythrocyte membrane such as osmotic resistance, membrane fluidity, and packing order of its hydrophilic area. Antioxidant activity of the extract was determined in relation to the erythrocyte membrane oxidized with free radicals induced by UVB and UVC radiation and the compound AAPH. Chromatographic, spectrophotometric and fluorimetric methods were applied in the research. The obtained results showed that kiwi leaves are a rich source of polyphenolic substances, mainly catechins and their dimers, which do not induce red blood cell hemolysis but make them stronger and more resistant to changes in medium tonicity. Substances contained in the extract effectively protect erythrocyte membranes against oxidation induced by physicochemical factors, the effectiveness of the protection depending on the concentration and type of free radical inducer. In addition, the study showed that the kiwi extract increases fluidity of the erythrocyte membrane and causes an increase in packing disorder in the hydrophilic membrane area. The changes seem to be due to the presence of polyphenolic substances in the extract, mainly in the region of the polar heads of lipids, where they can form a barrier protecting the membrane against diffusion of free radicals to the membrane interior. The effects of the extract evidenced by the present research, in particular protection of the biological membrane against free radicals induced by physicochemical agents, make it a potential valuable food additive, to enrich it with polyphenolic compounds that inhibit lipid oxidation in food exposed to UVB radiation. Supplementing the organism with substances contained in kiwi leaves is expected to provide protection against many diseases that develop as a result of oxidative stress.

Bystander effect induced by UVC radiation in Chinese hamster V79 cells

In past decades, researches on radiation-induced bystander effect mainly focused on ionizing radiation such as α-particle, β-particle, X-ray and γ-ray. But few researches have been conducted on the ability of ultraviolet (UV) radiation-induced bystander effect, and knowledge of UVC-induced bystander effect is far limited. Here, we adopted medium transfer experiment to detect whether UVC could cause bystander effect in Chinese hamster V79 cells. We determined the cell viability, apoptosis rate, chromosome aberration and ultrastructure changes, respectively. Our results showed that: (1) the viability of UVC-irradiated V79 cells declined significantly with the dosage of UVC; (2) similar to the irradiated cells, the main death type of bystander cells cultured in irradiation conditioned medium (ICMs) was also apoptosis; (3) soluble factors secreted by UVC-irradiated cells could induce bystander effect in V79 cells; (4) cells treated with 4 h ICM collected from 90 mJ cm(-2) UVC-irradiated cells displayed the strongest response. Our data revealed that UVC could cause bystander effect through the medium soluble factors excreted from irradiated cells and this bystander effect was a novel quantitative and kinetic response. These findings might provide a foundation to further explore the exact soluble bystander factors and detailed mechanism underlying UVC-induced bystander effect.

The role of Fpg protein in UVC-induced DNA lesions

We previously demonstrated that reactive oxygen species (ROS) could be involved in ultraviolet-C (UVC)-induced DNA damage in Escherichia coli cells. In the present study, we evaluated the involvement of the GO system proteins in the repair of the 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxoG, GO) lesion, which is ROS-induced oxidative damage. We first found that the mutant strain Δfur, which produces an accumulation of iron, and the cells treated with 2,2'-dipyridyl, a iron chelator, were both as resistant to UVC-induced lethality as the wild strain. The 8-oxoG could be mediated by singlet oxygen ((1)O(2)). The Fpg protein repaired this lesion when it was linked to C (cytosine), whereas the MutY protein repaired 8-oxoG when it was linked to A (adenine). The survival assay showed that the Fpg protein, but not the MutY protein, was important to UVC-induced lethality and interacted with the UvrA protein, a nucleotide excision repair (NER) protein involved in UVC repair. The GC-TA reversion assay in the mutant strains from the '8-oxoG-repair' GO system showed that UVC-induced mutagenesis in the fpg mutants, but not in the MutY strain. The transformation assay demonstrated that the Fpg protein is important in UVC repair. These results suggest that UVC could also cause indirect ROS-mediated DNA damage and the Fpg protein plays a predominant role in repairing this indirect damage.