The Surprising Diversity of UV-Induced Mutations.

Ultraviolet (UV) light is the most pervasive environmental mutagen and the primary cause of skin cancer. Genome sequencing of melanomas and other skin cancers has revealed that the vast majority of somatic mutations in these tumors are cytosine-to-thymine (C>T) substitutions in dipyrimidine sequences, which, together with tandem CC>TT substitutions, comprise the canonical UV mutation "signature". These mutation classes are caused by DNA damage directly induced by UV absorption, namely cyclobutane pyrimidine dimers (CPDs) or 6-4 pyrimidine-pyrimidone photoproducts (6-4PP), which form between neighboring pyrimidine bases. However, many of the key driver mutations in melanoma do not fit this mutation signature, but instead are caused by T>A, T>C, C>A, or AC>TT substitutions, frequently occurring in non-dipyrimidine sequence contexts. This article describes recent studies indicating that UV light causes a more diverse spectrum of mutations than previously appreciated, including many of the mutation classes observed in melanoma driver mutations. Potential mechanisms for these diverse mutation signatures are discussed, including UV-induced pyrimidine-purine photoproducts and indirect DNA damage induced by UVA light. Finally, the article reviews recent findings indicating that human DNA polymerase eta normally suppresses these non-canonical UV mutation classes, which can potentially explain why canonical C>T substitutions predominate in human skin cancers.

Aqueous photolysis of naproxen exposed to UV and natural sunlight: Formation of excited triplet and photosensitizing product.

Photochemical transformation is an important attenuation process for the non-steroidal anti-inflammatory drug naproxen (NPX) in both engineered and natural waters. Herein, we investigated the photolysis of NPX in aqueous solution exposed to both ultraviolet (UV, 254 nm) and natural sunlight irradiation. Results show that N2 purging significantly promoted NPX photolysis under UV irradiation, suggesting the formation of excited triplet state (3NPX*) as a critical transient. This inference was supported by benzophenone photosensitization and transient absorption spectra. Sunlight quantum yield of NPX was only one fourteenth of that under UV irradiation, suggesting the wavelength-dependence of NPX photochemistry. 3NPX* formed upon irradiation of NPX underwent photodecarboxylation leading to the formation of 2-(1-hydroxyethyl)-6-methoxynaphthalene (2HE6MN), 2-(1-hydroperoxyethyl)-6-methoxynaphthalene (2HPE6MN), and 2-acetyl-6-methoxynaphthalene (2A6MN). Notably, the conjugation and spin-orbit coupling effects of carbonyl make 2A6MN a potent triplet sensitizer, therefore promoting the photodegradation of the parent NPX. In hospital wastewater, the photolysis of NPX was influenced because the photoproduct 2A6MN and wastewater components could competitively absorb photons. Bioluminescence inhibition assay demonstrated that photoproducts of NPX exhibited higher toxicity than the parent compound. Results of this study provide new insights into the photochemical behaviors of NPX during UV treatment and in sunlit surface waters.

Structure-specific DNA endonuclease T7 endonuclease I cleaves DNA containing UV-induced DNA lesions.

The T7 gene 3 product, T7 endonuclease I, acts on various substrates with DNA structures, including Holliday junctions, heteroduplex DNAs and single-mismatch DNAs. Genetic analyses have suggested the occurrence of DNA recombination, replication and repair in Escherichia coli. In this study, T7 endonuclease I digested UV-irradiated covalently closed circular plasmid DNA into linear and nicked plasmid DNA, suggesting that the enzyme generates single- and double-strand breaks (SSB and DSB). To further investigate the biochemical functions of T7 endonuclease I, we have analysed endonuclease activity in UV-induced DNA substrates containing a single lesion, cyclobutane pyrimidine dimers (CPD) and 6-4 photoproducts (6-4PP). Interestingly, the leading cleavage site for CPD by T7 endonuclease I is at the second and fifth phosphodiester bonds that are 5' to the lesion of CPD on the lesion strand. However, in the case of 6-4PP, the cleavage pattern on the lesion strand resembled that of CPD, and T7 endonuclease I could also cleave the second phosphodiester bond that is 5' to the adenine-adenine residues opposite the lesion, indicating that the enzyme produces DSB in DNA containing 6-4PP. These findings suggest that T7endonuclease I accomplished successful UV damage repair by SSB in CPD and DSB in 6-4PP.

Ultraviolet Radiation Biological and Medical Implications.

Ultraviolet (UV) radiation plays a crucial role in the development of melanoma and non-melanoma skin cancers. The types of UV radiation are differentiated by wavelength: UVA (315 to 400 nm), UVB (280 to 320 nm), and UVC (100 to 280 nm). UV radiation can cause direct DNA damage in the forms of cyclobutane pyrimidine dimers (CPDs) and 6-4 photoproducts (6-4PPs). In addition, UV radiation can also cause DNA damage indirectly through photosensitization reactions caused by reactive oxygen species (ROS), which manifest as 8-hydroxy-2'-deoxyguanine (8-OHdG). Both direct and indirect DNA damage can lead to mutations in genes that promote the development of skin cancers. The development of melanoma is largely influenced by the signaling of the melanocortin one receptor (MC1R), which plays an essential role in the synthesis of melanin in the skin. UV-induced mutations in the BRAF and NRAS genes are also significant risk factors in melanoma development. UV radiation plays a significant role in basal cell carcinoma (BCC) development by causing mutations in the Hedgehog (Hh) pathway, which dysregulates cell proliferation and survival. UV radiation can also induce the development of squamous cell carcinoma via mutations in the TP53 gene and upregulation of MMPs in the stroma layer of the skin.

Selected widely prescribed pharmaceuticals: toxicity of the drugs and the products of their photochemical degradation to aquatic organisms.

Cholesterol-lowering drugs, antidiabetics, antiarrhythmics, antidepressants, and antibiotics belong to the most prescribed drugs worldwide. Because of the manufacture, excretion, and improper disposal of leftover drugs, the drugs enter waste waters and, subsequently, surface waters. They have been detected in surface waters all over the world, from concentrations of ng/l to concentrations several orders of magnitude higher. Since pharmaceuticals are designed to be both biologically and chemically stable, photochemical degradation by sun radiation represents a way of transformation in the natural environment. This review provides a survey of how selected drugs of the above-mentioned classes affect aquatic organisms of different trophic level. The emphasis is on the harmful effects of phototransformation products, an area of scientific investigation that has only attracted attention in the past few years, revealing the surprising fact that products of photochemical degradation might be even more toxic to aquatic organisms than the parent drugs.

Fluorinated Pharmaceutical and Pesticide Photolysis: Investigating Reactivity and Identifying Fluorinated Products by Combining Computational Chemistry,19F NMR, and Mass Spectrometry.

Fluorinated breakdown products from photolysis of pharmaceuticals and pesticides are of environmental concern due to their potential persistence and toxicity. While mass spectrometry workflows have been shown to be useful in identifying products, they fall short for fluorinated products and may miss up to 90% of products. Studies have shown that 19F NMR measurements assist in identifying and quantifying reaction products, but this protocol can be further developed by incorporating computations. Density functional theory was used to compute 19F NMR shifts for parent and product structures in photolysis reactions. Computations predicted NMR spectra of compounds with an R2 of 0.98. Computed shifts for several isolated product structures from LC-HRMS matched the experimental shifts with <0.7 ppm error. Multiple products including products that share the same shift that were not previously reported were identified and quantified using computational shifts, including aliphatic products in the range of -80 to -88 ppm. Thus, photolysis of fluorinated pharmaceuticals and pesticides can result in compounds that are polyfluorinated alkyl substances (PFAS), including aliphatic-CF3 or vinyl-CF2 products derived from heteroaromatic-CF3 groups. C-F bond-breaking enthalpies and electron densities around the fluorine motifs agreed well with the experimentally observed defluorination of CF3 groups. Combining experimental-computational 19F NMR allows quantification of products identified via LC-HRMS without the need for authentic standards. These results have applications for studies of environmental fate and analysis of fluorinated pharmaceuticals and pesticides in development.

Ketoprofen products induced photosensitization of sulfonamide antibiotics: The cocktail effects of pharmaceutical mixtures on their photodegradation.

Indirect photolysis induced by naturally occurring sensitizers constitutes an important pathway accounting for the transformation and fate of many recalcitrant micropollutants in sunlit surface waters. However, the photochemical transformation of micropollutants by photosensitizing pharmaceuticals has been less investigated. In this study, we demonstrated that the non-steroidal anti-inflammatory drug ketoprofen (KTF) and its photoproducts, 3-acetylbenzophenone (AcBP) and 3-ethylbenzophenone (EtBP), could sensitize the photodegradation of coexisting sulfonamide antibiotics, e.g., sulfamethoxazole (SMX), under artificial 365 nm ultraviolet (UV) and sunlight irradiation. Key reactive species including triplet excited state and singlet oxygen (1O2) responsible for photosensitization were identified by laser flash photolysis (LFP) and electron paramagnetic resonance (EPR) techniques, respectively. High-resolution mass spectrometry (HRMS) and structure-related reactivity analyses revealed that the sensitized photolysis of SMX occurred mainly through single electron transfer. The rate constants of sulfonamides sensitized by AcBP photolysis followed the order of sulfisoxazole (SIX)＞sulfathiazole (STZ)＞SMX＞sulfamethizole (SMT). Exposure to sunlight also enhanced the photolysis of SMX in the presence of KTF or AcBP, and water matrix had limited impact on such process. Overall, our results reveal the feasibility and mechanistic aspects of photosensitization of coexisting contaminants by pharmaceuticals (or their photoproducts) and provide new insights into the cocktail effects of pharmaceutical mixtures on their photochemical behaviors in aqueous environment.

Organic peroxyl radicals from biacetyl accelerated the visible-light degradation of steroid estrogens in aqueous solution.

Indirect photodegradation is an important pathway for the reduction of steroid estrogens in sunlit surface waters. Nevertheless, the kinetics and mechanisms governing the interaction between coexisting carbonyl compounds and estrogens under visible light (Vis) remain unexplored. This study systematically investigates the Vis-induced photodegradation of 17ß-estradiol (E2) in the presence of five specific carbonyl compounds-biacetyl (BD), acetone, glyoxal, pyruvic acid, and benzoquinone. The results demonstrate that, among these compounds, only BD significantly enhanced the photodegradation of E2 under Vis irradiation (λ > 400 nm). The pseudo-first order photodegradation rate constants (k1) of E2 in the Vis/BD system were 0.025 min-1 and 0.076 min-1 in ultrapure water and river water, respectively. The enhancing effect of BD was found to be pH-dependent, increasing the pH from 3.0 to 11.0 resulted in a 76% reduction in the k1 value of E2 in the Vis/BD system. Furthermore, the presence of humic acid, NO3-, or HCO3- led to an increase of more than 35% in the k1 value of E2, while NO2- exerted a pronounced inhibitory effect, resulting in a 92% decrease. Peroxyacetyl and peroxymethyl radicals, derived from BD in a yield ratio of 9, played a crucial role in the degradation of E2. These peroxyl radicals primarily targeted electron-rich hydroxyl sites of E2, initiating hydroxylation and ring-opening reactions that culminated in the formation of acidic byproducts. Notably, toxicity evaluation indicates that these hydroxylated and acidic products exhibited lower toxicity than the parent compound E2. This study highlights the important role of peroxyl radicals in estrogen degradation within aquatic environment, and also helps to design efficient visible light-responsive photo-activators for the treatment of estrogen-contaminated waters.

APE1-dependent base excision repair of DNA photodimers in human cells.

UV irradiation induces "bulky" DNA photodimers such as (6-4)-photoproducts and cyclobutane pyrimidine dimers that are removed by nucleotide excision repair, a complex process defective in the sunlight-sensitive and cancer-prone disease xeroderma pigmentosum. Some bacteria and lower eukaryotes can also repair photodimers by enzymatically simpler mechanisms, but such pathways have not been reported in normal human cells. Here, we have identified such a mechanism. We show that normal human cells can employ a DNA base excision repair process involving NTH1, APE1, PARP1, XRCC1, and FEN1 to rapidly remove a subset of photodimers at early times following UVC irradiation. Loss of these proteins slows the early rate of repair of photodimers in normal cells, ablates their residual repair in xeroderma pigmentosum cells, and increases UVC sensitivity ∼2-fold. These data reveal that human cells can excise photodimers using a long-patch base excision repair process that functions additively but independently of nucleotide excision repair.

First insights into 6PPD-quinone formation from 6PPD photodegradation in water environment.

p-Phenylenediamines (PPDs), an important type of rubber antioxidants, have received little study on their environmental fate, particularly for their vital photodegradation process in water environment. Accordingly, N-(1,3-dimethylbutyl)-N'-phenyl-1,4-phenylenediamine (6PPD), as a representative of PPDs, was investigated experimentally and theoretically for its photodegradation in water. Rapid photodegradation occurred when 6PPD was exposed to illumination especially UV region irradiation. Under acidic conditions, the photodegradation of 6PPD accelerated mainly due to the increased absorption of long wavelength irradiation by ionized 6PPD. Nine photodegradation products (e.g., 6PPD-quinone (6PPDQ)) of 6PPD were identified by an ultra-performance liquid chromatography QTOF mass spectrometry. Molar yields of photoproducts such as 6PPDQ, aniline, 4-aminodiphenylamine, and 4-hydroxydiphenylamine were 0.03 ± 0.00, 0.10 ± 0.01, 0.03 ± 0.02, and 0.08 ± 0.01, respectively. Mechanisms involved in 6PPD photodegradation include photoexcitation, direct photolysis, self-sensitized photodegradation, and 1O2 oxidation, as demonstrated by electron paramagnetic resonance (EPR) analysis, scavenging experiments, and the time-dependent density functional theory (TD-DFT). Notably, the toxicity of the reaction solution formed during the photodegradation of 6PPD was increased by the formation of highly toxic products (e.g., 6PPDQ). This study provides the first explanation for photodegradation mechanisms of 6PPD and confirms the pathway of 6PPDQ produced by the photoreaction in water environment.

Avoidance of the use of tryptophan in buried chromosomal proteins as a mechanism for reducing photo/oxidative damage to genomes.

In cells that are exposed to terrestrial sunlight, the indole moiety in the side chain of tryptophan (Trp) can suffer photo/oxidative damage (POD) by reactive oxygen species (ROS) and/or ultraviolet light (UV-B). Trp is oxidized to produce N-formylkynurenine (NFK), a UV-A-responsive photosensitizer that further degenerates into photosensitizers capable of generating ROS through exposure to visible light. Thus, Trp-containing proteins function as both victims, and perpetrators, of POD if they are not rapidly replaced through protein turnover. The literature indicates that protein turnover and DNA repair occur poorly in chromosomal interiors. We contend, therefore, that basic chromosomal proteins (BCPs) that are enveloped by DNA should have evolved to lack Trp residues in their amino acid sequences, since these could otherwise function as 'Trojan horse-type' DNA-damaging agents. Our global analyses of protein sequences demonstrates that BCPs consistently lack Trp residues, although DNA-binding proteins in general do not display such a lack. We employ HU-B (a wild-type, Trp-lacking bacterial BCP) and HU-B F47W (a mutant, Trp-containing form of the same bacterial BCP) to demonstrate that the possession of Trp is deleterious to BCPs and associated chromosomal DNA. Basically, we show that UV-B and UV-A (a) cause no POD in HU-B, but cause extensive POD in HU-B F47W (in vitro), as well as (b) only nominal DNA damage in bacteria expressing HU-B, but extensive DNA damage in bacteria expressing F47W HU-B (in vivo). Our results suggest that Trp-lacking BCPs could have evolved to reduce scope for protein-facilitated, sunlight-mediated damage of DNA by UV-A and visible light, within chromosomal interiors that are poorly serviced by protein turnover and DNA repair machinery.

Photodegradation of the Novel Herbicide Pyraquinate in Aqueous Solution: Kinetics, Photoproducts, Mechanisms, and Toxicity Assessment.

Pyraquinate, a newly developed 4-hydroxyphenylpyruvate dioxygenase class herbicide, has shown excellent control of resistant weeds in paddy fields. However, its environmental degradation products and corresponding ecotoxicological risks after field application remain ambiguous. In this study, we systematically investigate the photolytic behaviors of pyraquinate in aqueous solutions and in response to xenon lamp irradiation. The degradation follows first-order kinetics, and its rate depends on pH and the amount of organic matter. No vulnerability to light radiation is indicated. Ultrahigh-performance liquid chromatography with quadrupole-time-of-flight mass spectrometry and UNIFI software analysis reveals six photoproducts generated by methyl oxidation, demethylation, oxidative dechlorination, and ester hydrolysis. Gaussian calculation suggests that activities due to hydroxyl radicals or aquatic oxygen atoms caused these reactions on the premise of obeying thermodynamic criteria. Practical toxicity test results show that the toxicity of pyraquinate to zebrafish embryos is low but increases when the compound is combined with its photoproducts.

Wavelength-Dependent UV-LED Photolysis of Fluorinated Pesticides and Pharmaceuticals.

The wavelength dependence of photoproduct formation and quantum yields was evaluated for fluorinated pesticides and pharmaceuticals using UV-light emitting diodes (LEDs) with 255, 275, 308, 365, and 405 nm peak wavelengths. The fluorinated compounds chosen were saflufenacil, penoxsulam, sulfoxaflor, fluoxetine, 4-nitro-3-trifluoromethylphenol (TFM), florasulam, voriconazole, and favipiravir, covering key fluorine motifs (benzylic-CF3, heteroaromatic-CF3, aryl-F, and heteroaromatic-F). Quantum yields for the compounds were consistently higher for UV-C as compared to UV-A wavelengths and did not show the same trend as molar absorptivity. For all compounds except favipiravir and TFM, the fastest degradation was observed using 255 or 275 nm light, despite the low power of the LEDs. Using quantitative 19F NMR, fluoride, trifluoroacetate, and additional fluorinated byproducts were tracked and quantified. Trifluoroacetate was observed for both Ar-CF3 and Het-CF3 motifs and increased at longer wavelengths for Het-CF3. Fluoride formation from Het-CF3 was significantly lower as compared to other motifs. Ar-F and Het-F motifs readily formed fluoride at all wavelengths. For Het-CF3 and some Ar-CF3 motifs, 365 nm light produced either a greater number of or different major products. Aliphatic-CF2/CF3 products were stable under all wavelengths. These results assist in selecting the most efficient wavelengths for UV-LED degradation and informing future design of fluorinated compounds.

UV irradiation remodels the specificity landscape of transcription factors.

Somatic mutations are highly enriched at transcription factor (TF) binding sites, with the strongest trend being observed for ultraviolet light (UV)-induced mutations in melanomas. One of the main mechanisms proposed for this hypermutation pattern is the inefficient repair of UV lesions within TF-binding sites, caused by competition between TFs bound to these lesions and the DNA repair proteins that must recognize the lesions to initiate repair. However, TF binding to UV-irradiated DNA is poorly characterized, and it is unclear whether TFs maintain specificity for their DNA sites after UV exposure. We developed UV-Bind, a high-throughput approach to investigate the impact of UV irradiation on protein-DNA binding specificity. We applied UV-Bind to ten TFs from eight structural families, and found that UV lesions significantly altered the DNA-binding preferences of all the TFs tested. The main effect was a decrease in binding specificity, but the precise effects and their magnitude differ across factors. Importantly, we found that despite the overall reduction in DNA-binding specificity in the presence of UV lesions, TFs can still compete with repair proteins for lesion recognition, in a manner consistent with their specificity for UV-irradiated DNA. In addition, for a subset of TFs, we identified a surprising but reproducible effect at certain nonconsensus DNA sequences, where UV irradiation leads to a high increase in the level of TF binding. These changes in DNA-binding specificity after UV irradiation, at both consensus and nonconsensus sites, have important implications for the regulatory and mutagenic roles of TFs in the cell.

Genome-wide maps of rare and atypical UV photoproducts reveal distinct patterns of damage formation and mutagenesis in yeast chromatin.

Ultraviolet (UV) light induces different classes of mutagenic photoproducts in DNA, namely cyclobutane pyrimidine dimers (CPDs), 6-4 photoproducts (6-4PPs), and atypical thymine-adenine photoproducts (TA-PPs). CPD formation is modulated by nucleosomes and transcription factors (TFs), which has important ramifications for Ultraviolet (UV) mutagenesis. How chromatin affects the formation of 6-4PPs and TA-PPs is unclear. Here, we use UV damage endonuclease-sequencing (UVDE-seq) to map these UV photoproducts across the yeast genome. Our results indicate that nucleosomes, the fundamental building block of chromatin, have opposing effects on photoproduct formation. Nucleosomes induce CPDs and 6-4PPs at outward rotational settings in nucleosomal DNA but suppress TA-PPs at these settings. Our data also indicate that DNA binding by different classes of yeast TFs causes lesion-specific hotspots of 6-4PPs or TA-PPs. For example, DNA binding by the TF Rap1 generally suppresses CPD and 6-4PP formation but induces a TA-PP hotspot. Finally, we show that 6-4PP formation is strongly induced at the binding sites of TATA-binding protein (TBP), which is correlated with higher mutation rates in UV-exposed yeast. These results indicate that the formation of 6-4PPs and TA-PPs is modulated by chromatin differently than CPDs and that this may have important implications for UV mutagenesis.

Complementarity of two approaches based on the use of high-resolution mass spectrometry for the determination of multi-class antibiotics in water. Photodegradation studies and non-target screenings.

The development of analytical methodologies to monitor different antibiotic families in water and the implementation of alternatives for their efficient elimination are a great challenge. The aim of this research was to develop a method based on solid-phase extraction followed by ultra-high performance liquid chromatography coupled to quadrupole time-of-flight mass spectrometry to analyse multi-class antibiotics, including macrolides, cephalosporins, fluoroquinolones, sulfonamides and diaminopyrimidines, in waters. Several parameters affecting the extraction such as the sample pH, type of sorbent and cartridge, elution volume and breakthrough volume were optimized. The method was validated in real samples, and matrix effect was assessed, demonstrating that the use of isotopically labelled surrogate compounds was mandatory to avoid standard addition calibration for each individual samples. Urban and hospital wastewater samples, as well as natural waters, were analysed, confirming the presence of 12 of the 14 target compounds at concentrations up to 3.5 µg L-1. Non-target analysis based on data-independent workflow was also performed, enabling the identification of 94 pollutants. Preliminary photodegradation experiments were also assessed, revealing the total removal of many target compounds after the first 5-10 min of UVC irradiation. In addition, 20 by-products formed after photolysis could be identified using a non-target approach.

Aquatic photolysis of the pharmaceutical ambroxol: The role of 2,4-dibromoaniline chromophore and heavy atom effect of bromine.

As one of the most effective expectorant class drugs, ambroxol (AMB) has been frequently used to treat acute and chronic bronchitis. Extensive use and human excretion result in the widespread occurrence of AMB in wastewater. Herein, we reported the photolysis of AMB in aqueous solution upon 254 nm ultraviolet radiation (UV254). Spectroscopic characterization showed that 2,4-dibromoaniline (DBA) moiety is the core chromophore of AMB. Quantum yield of DBA changed little at pH 4.0 - 9.0; however, AMB showed higher quantum yield at pH > 8.0. Both DBA and AMB have high photoreactivity, which can be attributed to the "heavy atom" effect of bromine substituents. The photolysis of AMB occurred through photoreduction, photoionization, photonucleophilic substitution, side-chain cleavage, and coupling reactions. Both AMB and DBA underwent debromination with yields reaching 80% under 3200 mJ cm-2 UV fluence. Photo-debromination occurred preferentially at the para-position. The presence of natural organic matter inhibited the photodegradation, mainly due to the light-screening effect. The photolysis of AMB was slightly enhanced in the presence of NO3- likely due to radical-induced oxidation. Bioluminescence inhibition assay revealed that photoproducts were not toxic. The results show that UV254 radiation with fluences relevant to advanced oxidation processes was effective for the abatement of AMB in wastewater. However, UV254 treatment of wastewater containing higher concentrations (˃ µg L-1) of AMB should be done with caution because the released Br- can be converted to toxic brominated disinfection byproducts and bromate in subsequent oxidation process.

Uptake of UVc induced photoproducts of dipicolinic acid by Bacillus subtilis spores - Effects on the germination and UVc resistance of the spores.

Dipicolinic acid (DPA) is a specific molecule of bacterial spores which is essential to their resistance to various stresses such as ultraviolet (UV) exposure and to their germination. DPA has a particular photochemistry that remains imperfectly understood. In particular, due to its ability to absorb UVc radiation, it is likely to form in vitro a wide variety of photoproducts (DPAp) of which only about ten have been recently identified. The photochemical reactions resulting in DPAp, especially those inside the spores, are still poorly understood. Only one of these DPAp, which probably acts as a photosensitizer of DNA upon exposure to UVc, has been identified as having an impact on spores. However, as UVc is required to form DPAp, it is difficult to decouple the overall effect of UVc exposure from the possible effects of DPAp alone. In this study, DPAp were artificially introduced into the spores of the FB122 mutant strain of Bacillus subtilis, one that does not produce DPA. These experiments revealed that some DPAp may play a positive role for the spore. These benefits are visible in an improvement in spore germination rate and kinetics, as well as in an increase in their resistance to UVc exposure.

Aluminum (Al) causes a delayed suppression of nucleotide excision repair (NER) capacity in zebrafish (Danio rerio) embryos via disturbance of DNA lesion detection.

Aluminum (Al) is extensively used for making cooking utensils and its presence in the aquatic environment may occur through acid mine drainage and wastewater discharge. Al is known to induce genotoxicity in human cells, rodents, and fish. Nucleotide excision repair (NER) eliminates helix-twisting DNA lesions such as UV-induced dipyrimidine photoproducts. Because our earlier investigation revealed the operation of NER in zebrafish (Danio rerio) embryos, this study explored if inhibition of NER could be a mechanism of Al-induced genotoxicity using zebrafish embryo as a model system. An acute fish embryo toxicity test indicated that Al (as aluminum sulfate) at 2-15 mg/L were nonlethal to zebrafish embryos, yet exposure of embryos at 1 h post fertilization (hpf) to Al at 10-15 mg/L for 71 h significantly repressed their NER capacity monitored by a transcription-based DNA repair assay. Band shift analysis indicated a higher sensitivity of (6-4) photoproduct (6-4PP) than cyclobutane pyrimidine dimer (CPD) detecting activities to Al, reflecting the preferential influence of Al on the detection of strongly distorted DNA lesions. Time-course experiments showed a delayed response of NER to Al as repair machinery was unaffected by Al at 15 mg/L following a 35-h exposure, while Al treatment for the same period obviously inhibited 6-4PP binding activities although the gene expression of damage recognition factors remained active. Inhibition of 6-4PP detection blocked downstream lesion incision/excision detected by a terminal deoxy transferase-mediated end labeling assay. As the disturbance of damage sensing preceded that of the overall repair process, Al exposure was believed to downregulate NER capacity by inhibiting the activities of lesion detection proteins. Our results revealed the ability of Al to enhance its genotoxicity by suppressing NER capacity.

Spectroscopic and microscopic characterization of dipicolinic acid and its salt photoproducts - A UVc effect study on DPA in solution and in bacterial spores.

Bacterial spores can cause significant problems such as food poisoning (like neurotoxin or emetic toxin) or serious illnesses (like anthrax or botulism). This dormant form of bacteria, made of several layers of barriers which provide extreme resistance to many abiotic stresses (radiation, temperature, pressure, etc.), are difficult to investigate in situ. To better understand the biological and chemical mechanisms involved and specific to spores resistance, the acquisition of environmental parameters is necessary. For that purpose, our research has been focused on the detection and analysis of a unique spore component, dipicolinic acid (DPA), used as the main in situ metabolite for sporulating bacteria detection. In its native form, DPA is only weakly fluorescent but after Ultraviolet irradiation at the wavelength of 254 nm (UVc), DPA photoproducts (DPAp) exhibit a remarkable fluorescence signal. These photoproducts are rarely identified and part of this study gives new insights offered by mass spectrometry (MS) in the determination of DPA photoproducts. Thanks to DPA assay techniques and fluorescence spectrometry, we highlighted the instability of photoproducts and introduced new assumptions on the effects of UVc on DPA. Studies in spectroscopy and microscopy allowed us to better understand these native probes in bacterial spores and will allow the implementation of a new method for studying the physico-chemical parameters of spore resistance.