Extremely high intracellular concentration of glucose-6-phosphate and NAD(H) in Deinococcus radiodurans

Current insights and future perspectives of ultraviolet radiation (UV) exposure: Friends and foes to the skin and beyond the skin

Ultraviolet (UV) radiation is ubiquitous in the environment, which has been classified as an established human carcinogen. As the largest and outermost organ of the body, direct exposure of skin to sunlight or UV radiation can result in sunburn, inflammation, photo-immunosuppression, photoaging and even skin cancers. To date, there are tactics to protect the skin by preventing UV radiation and reducing the amount of UV radiation to the skin. Nevertheless, deciphering the essential regulatory mechanisms may pave the way for therapeutic interventions against UV-induced skin disorders. Additionally, UV light is considered beneficial for specific skin-related conditions in medical UV therapy. Recent evidence indicates that the biological effects of UV exposure extend beyond the skin and include the treatment of inflammatory diseases, solid tumors and certain abnormal behaviors. This review mainly focuses on the effects of UV on the skin. Moreover, novel findings of the biological effects of UV in other organs and systems are also summarized. Nevertheless, the mechanisms through which UV affects the human organism remain to be fully elucidated to achieve a more comprehensive understanding of its biological effects.

Antioxidant defense of Deinococcus radiodurans: how does it contribute to extreme radiation resistance?

PURPOSE

Deinococcus radiodurans is an extremely radioresistant bacterium characterized by D10 of 10 kGy, and able to grow luxuriantly under chronic ionizing radiation of 60 Gy/h. The aim of this article is to review the antioxidant system of D. radiodurans and its possible role in the unusual resistance of this bacterium to ionizing radiation.

CONCLUSIONS

The unusual radiation resistance of D. radiodurans has apparently evolved as a side effect of the adaptation of this extremophile to other damaging environmental factors, especially desiccation. The antioxidant proteins and low-molecular antioxidants (especially low-molecular weight Mn2+ complexes and carotenoids, in particular, deinoxanthin), as well as protein and non-protein regulators, are important for the antioxidant defense of this species. Antioxidant protection of proteins from radiation inactivation enables the repair of DNA damage caused by ionizing radiation.

Thiol Reductases in Deinococcus Bacteria and Roles in Stress Tolerance

Deinococcus species possess remarkable tolerance to extreme environmental conditions that generate oxidative damage to macromolecules. Among enzymes fulfilling key functions in metabolism regulation and stress responses, thiol reductases (TRs) harbour catalytic cysteines modulating the redox status of Cys and Met in partner proteins. We present here a detailed description of Deinococcus TRs regarding gene occurrence, sequence features, and physiological functions that remain poorly characterised in this genus. Two NADPH-dependent thiol-based systems are present in Deinococcus. One involves thioredoxins, disulfide reductases providing electrons to protein partners involved notably in peroxide scavenging or in preserving protein redox status. The other is based on bacillithiol, a low-molecular-weight redox molecule, and bacilliredoxin, which together protect Cys residues against overoxidation. Deinococcus species possess various types of thiol peroxidases whose electron supply depends either on NADPH via thioredoxins or on NADH via lipoylated proteins. Recent data gained on deletion mutants confirmed the importance of TRs in Deinococcus tolerance to oxidative treatments, but additional investigations are needed to delineate the redox network in which they operate, and their precise physiological roles. The large palette of Deinococcus TR representatives very likely constitutes an asset for the maintenance of redox homeostasis in harsh stress conditions.

Insights into Glucose-6-phosphate Allosteric Activation of β-Glucosidase A

Second-generation ethanol production involves the use of agricultural and forestry waste as feedstock, being an alternative to the first-generation technology as it relies on low-cost abundant residues and does not affect food agriculture. However, the success of second-generation biorefineries relies on energetically efficient processes and effective enzyme cocktails to convert cellulose into fermentable sugars. β-glucosidases catalyze the last step on the enzymatic hydrolysis of cellulose; however, they are often inhibited by glucose. Previous studies demonstrated that glucose-6-phosphate (G6P) is a positive allosteric modulator of Bacillus polymyxa β-glucosidase A, improving enzymatic efficiency, providing thermoresistance, and imparting glucose tolerance. However, the precise molecular details of G6P-β-glucosidase A interactions have not yet been described so far. We investigated the molecular details of G6P binding into B. polymyxa β-glucosidase A through in silico docking using the site identification by ligand competitive saturation technology followed by site-directed mutagenesis studies, from which an allosteric binding site for G6P was identified. In addition, a mechanistic shift toward the transglycosylation reaction as opposed to hydrolysis was observed in the presence of G6P, suggesting a new role of G6P allosteric modulation of the catalytic activity of β-glucosidase A.

Enhanced Lycopene Production by UV-C Irradiation in Radiation-Resistant Deinococcus radiodurans R1

Although classical metabolic engineering strategies have succeeded in developing microbial strains capable of producing desired bioproducts, metabolic imbalance resulting from extensive genetic manipulation often leads to decreased productivity. Thus, abiotic strategies for improving microbial production performance can be an alternative to overcome drawbacks arising from intensive metabolic engineering. Herein, we report a promising abiotic method for enhancing lycopene production by UV-C irradiation using a radiation-resistant ΔcrtLm/crtB⁺dxs⁺ Deinococcus radiodurans R1 strain. First, the onset of UV irradiation was determined through analysis of the expression of 11 genes mainly involved in the carotenoid biosynthetic pathway in the ΔcrtLm/crtB⁺dxs⁺ D. radiodurans R1 strain. Second, the effects of different UV wavelengths (UV-A, UV-B, and UV-C) on lycopene production were investigated. UV-C irradiation induced the highest production, resulting in a 69.9% increase in lycopene content [64.2 ± 3.2 mg/g dry cell weight (DCW)]. Extended UV-C irradiation further enhanced lycopene content up to 73.9 ± 2.3 mg/g DCW, a 95.5% increase compared to production without UV-C irradiation (37.8 ± 0.7 mg/g DCW).

High-Yield Production of Lycopene from Corn Steep Liquor and Glycerol Using the Metabolically Engineered Deinococcus radiodurans R1 Strain

Developing a highly efficient and ecofriendly system to produce desired products from waste can be considered important to a sustainable society. Here, we report for the first time high-yield production of lycopene through metabolically engineering an extremophilic microorganism, Deinococcus radiodurans R1, from corn steep liquor (CSL) and glycerol. First, the crtLm gene-encoding lycopene cyclase was deleted to prevent the conversion of lycopene to γ-carotene. Then, the crtB gene-encoding phytoene synthase and the dxs gene-encoding 1-deoxy-d-xylulose 5-phosphate synthase were overexpressed to increase carbon flux toward lycopene. The engineered ΔcrtLm/crtB⁺dxs⁺ D. radiodurans R1 could produce 273.8 mg/L [80.7 mg/g dry cell weight (DCW)] and 373.5 mg/L (108.0 mg/g DCW) of lycopene from 10 g/L of glucose with 5 g/L of yeast extract and 9.9 g/L of glucose with 20 g/L of CSL, respectively. Moreover, the lycopene titer and content were increased by 26% (470.6 mg/L) and 28% (138.2 mg/g DCW), respectively, when the carbon source was changed to glycerol. Finally, fed-batch fermentation of the final engineered strain allowed the production of 722.2 mg/L (203.5 mg/g DCW) of lycopene with a yield and productivity of 20.3 mg/g glycerol and 6.0 mg/L/h, respectively, from 25 g/L of CSL and 35.7 g/L of glycerol.