Effect of Extracellular Tyrosinase on the Expression Level of P450, Fpr, and Fdx and Ortho-hydroxylation of Daidzein in Streptomyces avermitilis

Biotechnological Production and Characterization of Extracellular Melanin by Streptomyces nashvillensis

Melanins are pigments employed in food, cosmetic, and textile industries, manufactured by extraction from cuttlefishes. Their biotechnological production by Streptomycetes, instead, has been poorly investigated so far. In this paper, for the first time, the strain Streptomyces nashvillensis DSM 40314 was tested as an extracellular melanin producer by investigating the influence of diverse temperatures (26, 28, and 30 °C) and pH values (6.0 and 7.0) on bacterial growth, melanin production, and on the activity of the secreted tyrosinase, the first enzyme of the pigment biosynthetic pathway. In physiological 96-h shake flask experiments, the optimal growth parameters resulted to be 28 °C and pH 7.0, at which a maximum biomass of 8.4 ± 0.5 gcdw/L, a melanin concentration of 0.74 ± 0.01 g/L (yield on biomass of 0.09 ± 0.01 g/gcdw and productivity of 0.008 ± 0.001 g/L/h), and a final tyrosinase activity of 10.1 ± 0.1 U/mL were reached. The produced pigment was purified from the broth supernatant with a two-step purification process (75.0 ± 2.0% of purity with 65.0 ± 5.0% of recovery) and tested for its chemical, antioxidant, and photoprotective properties. Finally, characterization by UV-visible and FT-IR spectroscopy, elemental analyses, and mono- and bi-dimensional NMR suggested the eumelanin-like nature of the pigment.

The Novel Role of Tyrosinase Enzymes in the Storage of Globally Significant Amounts of Carbon in Wetland Ecosystems

Over the last millennia, wetlands have been sequestering carbon from the atmosphere via photosynthesis at a higher rate than releasing it and, therefore, have globally accumulated 550 × 10¹⁵ g of carbon, which is equivalent to 73% of the atmospheric carbon pool. The accumulation of organic carbon in wetlands is effectuated by phenolic compounds, which suppress the degradation of soil organic matter by inhibiting the activity of organic-matter-degrading enzymes. The enzymatic removal of phenolic compounds by bacterial tyrosinases has historically been blocked by anoxic conditions in wetland soils, resulting from waterlogging. Bacterial tyrosinases are a subgroup of oxidoreductases that oxidatively remove phenolic compounds, coupled to the reduction of molecular oxygen to water. The biochemical properties of bacterial tyrosinases have been investigated thoroughly in vitro within recent decades, while investigations focused on carbon fluxes in wetlands on a macroscopic level have remained a thriving yet separated research area so far. In the wake of climate change, however, anoxic conditions in wetland soils are threatened by reduced rainfall and prolonged summer drought. This potentially allows tyrosinase enzymes to reduce the concentration of phenolic compounds, which in turn will increase the release of stored carbon back into the atmosphere. To offer compelling evidence for the novel concept that bacterial tyrosinases are among the key enzymes influencing carbon cycling in wetland ecosystems first, bacterial organisms indigenous to wetland ecosystems that harbor a TYR gene within their respective genome (tyr⁺) have been identified, which revealed a phylogenetically diverse community of tyr⁺ bacteria indigenous to wetlands based on genomic sequencing data. Bacterial TYR host organisms covering seven phyla (Acidobacteria, Actinobacteria, Bacteroidetes, Firmicutes, Nitrospirae, Planctomycetes, and Proteobacteria) have been identified within various wetland ecosystems (peatlands, marshes, mangrove forests, bogs, and alkaline soda lakes) which cover a climatic continuum ranging from high arctic to tropic ecosystems. Second, it is demonstrated that (in vitro) bacterial TYR activity is commonly observed at pH values characteristic for wetland ecosystems (ranging from pH 3.5 in peatlands and freshwater swamps to pH 9.0 in soda lakes and freshwater marshes) and toward phenolic compounds naturally present within wetland environments (p-coumaric acid, gallic acid, protocatechuic acid, p-hydroxybenzoic acid, caffeic acid, catechin, and epicatechin). Third, analyzing the available data confirmed that bacterial host organisms tend to exhibit in vitro growth optima at pH values similar to their respective wetland habitats. Based on these findings, it is concluded that, following increased aeration of previously anoxic wetland soils due to climate change, TYRs are among the enzymes capable of reducing the concentration of phenolic compounds present within wetland ecosystems, which will potentially destabilize vast amounts of carbon stored in these ecosystems. Finally, promising approaches to mitigate the detrimental effects of increased TYR activity in wetland ecosystems and the requirement of future investigations of the abundance and activity of TYRs in an environmental setting are presented.

Reviewing a plethora of oxidative-type reactions catalyzed by whole cells of Streptomyces species

Selective oxidation reactions represent a challenging task for conventional organic chemistry. Whole-cell biocatalysis provides a very convenient, easy to apply method to carry out different selective oxidation reactions including chemo-, regio-, and enantio-selective reactions. Streptomyces species are important biocatalysts as they can catalyze these selective reactions very efficiently owing to the wide diversity of enzymes and enzymatic cascades in their cell niche. In this review, we present and analyze most of the examples reported to date of oxidative reactions catalyzed by Streptomyces species as whole-cell biocatalysts. We discuss 33 different Streptomyces species and strains and the role they play in different oxidative reactions over the past five decades. The oxidative reactions have been classified into seven categories that include: hydroxylation of steroids/non-steroids, asymmetric sulfoxidations, oxidation of aldehydes, multi-step oxidations, oxidative cleavage, and N-oxidations. The role played by Streptomyces species as recombinant hosts catalyzing bio-oxidations has also been highlighted.

Dual-Channel Fluorescence Imaging of Hydrogel Degradation and Tissue Regeneration in the Brain

The ability of brain tissue to regenerate is limited; therefore, brain diseases (i.e., trauma, stroke, tumors) often lead to irreversible motor and cognitive impairments. Therapeutic interventions using various types of injectable biomaterials have been investigated to promote endogenous neural differentiation. Despite promising results in pre-clinical studies, the translation of regenerative medicine to the clinic has many challenges due to the lack of reliable imaging systems to achieve accurate evaluation of the treatment efficacy.

Methods: In this study, we developed a dual-channel fluorescence imaging technique to simultaneously monitor tissue ingrowth and scaffold disintegration. Enzymatically crosslinked gelatin-hyaluronic acid hydrogel was labeled with 800 nm fluorophore, ZW800-3a, while the regenerated tissue was highlighted with 700 nm brain-specific contrast agent, Ox1.

Results: Using the multichannel fluorescence imaging system, tissue growth and degradation of the NIR hydrogel were simultaneously imaged in the brain of mice. Images were further analyzed and reconstructed to show both visual and quantitative information of each stage of a therapeutic period.

Conclusion: Dual-channel in vivo imaging systems can provide highly accurate visual and quantitative information of the brain tissue ingrowth for the evaluation of the therapeutic effect of NIR hydrogel through a simple and fast operating procedure.