Photodynamic action of phycocyanin: Damage and repair

Panoptic elucidation of algicidal mechanism of Raoultella sp. S1 against the Microcystis aeruginosa by TMT quantitative proteomics

Harmful algal blooms (HABs) due to eutrophication are becoming a serious ecological disaster worldwide, threatening human health and the optimal balance of aquatic ecosystems. The traditional approaches to eradicate HABs yield several drawbacks in practical application, while microbial algicidal technology is garnering mounting recognition due to its high efficiency, eco-friendliness, and low cost. In our previous study, we isolated a bacterium strain Raoultella sp. S1 from eutrophic water with high efficiency of algicidal properties. This study further investigated the flocculation and inactivation efficiency of S1 on Microcystis aeruginosa at different eutrophic stages by customizing the algal cell densities. The supernatant extract of S1 strain exhibited remarkable flocculation and inactivation effects against low (1 × 106 cell/mL)and medium (2.7 × 106 cell/mL)concentrations of algal cells, but unexceptional for higher densities. The results further revealed that algal cells at low and medium counts manifested a more apparent antioxidant defense response, while the photosynthetic efficiency and relative electron transport rate were considerably reduced within 24 h. TEM observations confirmed the disruption of thylakoid membranes and cell structure of algal cells by algicidal substances. Moreover, TMT proteomics revealed alterations in protein metabolic pathways of algal cells during the flocculation and lysis stages at the molecular biological level. This signified that the disruption of the photosynthetic system is the core algicidal mechanism of S1 supernatant. In contrast, the photosynthetic metabolic pathways in the HABs were significantly upregulated, increasing the energy supply for the NADPH dehydrogenation process and the upregulation of ATPases in oxidative phosphorylation. Insufficient energy provided by NADPH resulted in a dwindled electron transport rate, stagnation of carbon fixation in dark reactions, and blockage of light energy conversion into chemical energy. Nonetheless, carbohydrate metabolism (gluconeogenesis and glycolysis) proteins were down-regulated and hampered DNA replication and repair. This study aided in unveiling the bacterial management of eutrophication by Raoultella sp. S1 and further arrayed the proteomic mechanism of algal apoptosis.

Enhanced phycocyanin and DON removal by the synergism of H2O2 and micro-sized ZVI: Optimization, performance, and mechanisms

Micro-sized zero-valent iron (mZVI) has proven effective for phycocyanin (PC) removal, but efficiency needs to be enhanced. Here, hydrogen peroxide (H₂O₂) was used to enhance PC removal by mZVI and the corresponding mechanisms are discussed. The results showed that H₂O₂ could effectively enhance PC removal by mZVI and the PC removal efficiency increased from 37.8% to 80.6% with 1.5 g/L mZVI in 60 min reaction time. The trends of dissolved organic nitrogen (DON) removal were consistent with PC removal. Low pH value, high mZVI dosage, and a suitable amount of H₂O₂ were conducive to PC removal. The SEM-mapping indicated that PC removal was not primarily by adsorption. Similarly, no obvious change was observed in PC molecular structure based on fluorescence spectroscopy and SDS-PAGE analyses. However, the PC removal mechanism could be inferred from the variation of iron concentration in the process. The coagulation of dissolved iron ions dissolved from mZVI was the main removal pathway. The OH oxidation only accounted for 20% of PC removal. PC removal led to the reduction of disinfection by-products with similar efficiency. The combination of mZVI and H₂O₂ is a promising strategy for the simultaneous removal of PC and DON in drinking water treatments.

Removal efficiency and mechanism of phycocyanin in water by zero-valent iron

The efficiencies and mechanism of phycocyanin removal from water by zero-valent iron (ZVI) were studied. The trend for dissolved organic nitrogen removal was similar to phycocyanin and the removal efficiency was high at ∼81% and 95%, respectively, in 90 min. The experimental results showed that the phycocyanin removal efficiency was higher at pH < 6, with an almost complete removal. However, only 68% was removed at pH 9. Within 30 min, the removal efficiency of phycocyanin for 1-4 tested cycles was reduced from 55.8% to 15.2%. Scanning electron microscopy and energy dispersive spectroscopy, Fourier transform infrared spectroscopy analysis and X-ray photoelectron spectroscopy were used to analyze the mechanisms of phycocyanin removal, which indicated that a small amount of phycocyanin was immobilized on the ZVI surface by adsorption. In addition, the main removal pathway was coagulation by dissolved iron ions. The Fe oxide formed in situ from ZVI had a higher removal efficiency than that in FeCl₃, which can play improved roles in charge neutralization. The production of disinfection byproducts also decreased because of the decrease of precursors.

Enzymatic recognition of DNA damage induced by UVB-photosensitized titanium dioxide and biological consequences in Saccharomyces cerevisiae: evidence for oxidatively DNA damage generation

Although titanium dioxide (TiO(2)) has been considered to be biologically inert, finding use in cosmetics, paints and food colorants, recent reports have demonstrated that when TiO(2) is attained by UVA radiation oxidative genotoxic and cytotoxic effects are observed in living cells. However, data concerning TiO(2)-UVB association is poor, even if UVB radiation represents a major environmental carcinogen. Herein, we investigated DNA damage, repair and mutagenesis induced by TiO(2) associated with UVB irradiation in vitro and in vivo using Saccharomyces cerevisiae model. It was found that TiO(2) plus UVB treatment in plasmid pUC18 generated, in addition to cyclobutane pyrimidine dimers (CPDs), specific damage to guanine residues, such as 8-oxo-7,8-dihydroguanine (8-oxoG) and 2,6-diamino-4-hydroxy-5-formamidopyrimidine (FapyG), which are characteristic oxidatively generated lesions. In vivo experiments showed that, although the presence of TiO(2) protects yeast cells from UVB cytotoxicity, high mutation frequencies are observed in the wild-type (WT) and in an ogg1 strain (deficient in 8-oxoG and FapyG repair). Indeed, after TiO(2) plus UVB treatment, induced mutagenesis was drastically enhanced in ogg1 cells, indicating that mutagenic DNA lesions are repaired by the Ogg1 protein. This effect could be attenuated by the presence of metallic ion chelators: neocuproine or dipyridyl, which partially block oxidatively generated damage occurring via Fenton reactions. Altogether, the results indicate that TiO(2) plus UVB potentates UVB oxidatively generated damage to DNA, possibly via Fenton reactions involving the production of DNA base damage, such as 8-oxo-7,8-dihydroguanine.

Does UVB radiation induce SoxS gene expression in Escherichia coli cells?

The SoxRS regulon is induced when bacterial cells are exposed to redox-cycling agents such as menadione or paraquat. In this paper it is shown that a physical agent, such as ultraviolet radiation with a wavelength of 312 nm (UVB) can induce soxS gene expression. The results indicate that this induction involves the RpoS protein. Moreover, an unexpected increase of soxS gene expression independent of a functional soxR gene in UVB-irradiated cells has been verified. This increase could be explained by transcription of soxS gene in a rpoS-dependent pathway.

The effect of electromagnetic field exposure on the formation of DNA lesions

In an attempt to determine whether electromagnetic field (EMF) exposure might lead to DNA damage, we exposed SnCl2-treated pBR322 plasmids to EMF and analysed the resulting conformational changes using agarose gel electrophoresis. An EMF-dependent potentiation of DNA scission (i.e. the appearance of relaxed plasmids) was observed. In confirmation of this, plasmids pre-exposed to EMF also were less capable of transforming Escherichia coli. The results indicate that EMF, in the presence of a transition metal, is capable of causing DNA damage. These observations support the idea that EMF, probably through secondary generation of reactive oxygen species, can be clastogenic and provide a possible explanation for the observed correlation between EMF exposure and the frequency of certain types of cancers in humans.

H2O2-induced cross-protection against UV-C killing in Escherichia coli is blocked in a lexA (Def) background

Pretreatment with 2.5 mM H2O2 protects E. coli cells against UV-C killing, a phenomenon independent of LexA cleavage. In this paper, we observe that this cross-protection response is neither dependent on the dinY gene product nor on the system that controls dinY, since H2O2 is able to induce cross-protection but not to induce the dinY gene in a lexA-noninducible strain [lexA (Ind-)]. Moreover, this response is not induced in a lexA (Def) background, suggesting that the expression of the SOS regulon may inhibit this cross-protection response.

Shark cartilage-containing preparation: protection against reactive oxygen species

There is overwhelming evidence to indicate that free radicals cause oxidative damage to lipids, proteins and nucleic acids and are involved in the pathogenesis of several degenerative diseases. Therefore, antioxidants, which can neutralize free radicals, may be of central importance in the prevention of these disease states. The protection that fruits and vegetables provide against disease has been attributed to the various antioxidants contained in them. Recently, an anti-inflammatory and analgesic activity of a water-soluble fraction from shark cartilage has been described. Using electrophoretical assays, bacteria survival and transformation and the Salmonella/mammalian-microsome assay, we investigated the putative role of shark cartilage-containing preparation in protecting cells against reactive oxygen species induced DNA damage and mutagenesis. If antimutagens are to have any impact on human disease, it is essential that they are specifically directed against the most common mutagens in daily life. Our data suggest that shark cartilage-containing preparation can play a scavenger role for reactive oxygen species and protects cells against inactivation and mutagenesis.

Enzymatic recognition and biological effects of photodynamic damage induced in DNA by 1,6-dioxapyrene plus UVA

The specific recognition of DNA modifications by repair endonucleases was used to characterize DNA damage induced by 1,6-dioxapyrene (1,6-DP) in the presence of ultraviolet light at 365 nm (UVA) in the plasmid YEplac181. Under cell free conditions, 1,6-DP plus UVA generated lesions are recognized by the UvrABC endonuclease, the proteins Nth, Nfo and Fpg. The number of UvrABC sensitive sites was at least ten-fold higher than that of Fpg or Nth sensitive sites. Moreover, 1,6-DP plus UVA generated single-strand breaks which are the second most frequent lesions. To investigate the biological effect of DNA damage, YEplac181 DNA was treated with 1,6-DP plus UVA and transformed into Escherichia coli or Saccharomyces cerevisiae. In Escherichia coli, the transformation efficiency of 1,6-DP plus UVA treated DNA was greatly reduced in the uvrA mutant compared to that in the wild-type strain. However, the transforming efficiency was not affected in Fpg-deficient strains. In Saccharomyces cerevisiae, the transformation efficiency of 1,6-DP plus UVA treated YEplac181 was greatly reduced in the rad14::URA3 strain. The photobiological effect of 1,6-DP plus UVA was also analysed in haploid yeast strains of various repair capacities. The results show that the yeast strain defective in the nucleotide excision repair pathway (rad14::URA3) is hypersensitive to 1,6-DP plus UVA treatment as compared to the parental wild-type strain. It is confirmed that the lethal effect of 1,6-DP plus UVA on wild-type yeast is strongly oxygen dependent, whereas the survival of the rad14::URA3 mutant only exhibits a minor oxygen dependence. To conclude, our data show that the photodynamic DNA lesions induced by 1,6-DP plus UVA can be recognized and repaired in pro- and eukaryotic cells by the nucleotide excision repair pathway.