Effects of Efficient Expression of Vitreoscilla Hemoglobin on Production, Monosaccharide Composition, and Antioxidant Activity of Exopolysaccharides in Ganoderma lucidum

A Vitreoscilla hemoglobin (VHb) gene was efficiently expressed by the optimization of codons and intron addition in G. lucidum. Expression of the VHb gene was confirmed by genome PCR, quantitative real-time PCR and carbon monoxide (CO)-difference spectrum analysis in the transformant. The effects of the efficient expression of VHb gene on production, monosaccharide compostion, and antioxidant activity of G. lucidum exopolysaccharides were studied. The maximum production of exopolysaccharides in the VHb gene-bearing transformant was 1.63 g/L, which was 1.5-fold higher than expression in the wild-type strain. Efficient expression of the VHb gene did not change the monosaccharide composition or distribution of molecular weight, but it increased the mole percentage ratio of galactose and mannose in G. lucidum exopolysaccharide. Exopolysaccharides from the transformant had higher scavenging 2,2-diphenyl-1-picrylhydrazyl (DPPH) and hydroxyl (OH) radical capacity and reducing power than those from the wild-type strain. These results may be helpful for increasing production and application of exopolysaccharides produced by G. lucidum fermentation.

Recent Advances in the Physicochemical Properties and Biotechnological Application of Vitreoscilla Hemoglobin

Vitreoscilla hemoglobin (VHb), the first discovered bacterial hemoglobin, is a soluble heme-binding protein with a faster rate of oxygen dissociation. Since it can enhance cell growth, product synthesis and stress tolerance, VHb has been widely applied in the field of metabolic engineering for microorganisms, plants, and animals. Especially under oxygen-limited conditions, VHb can interact with terminal oxidase to deliver enough oxygen to achieve high-cell-density fermentation. In recent years, with the development of bioinformatics and synthetic biology, several novel physicochemical properties and metabolic regulatory effects of VHb have been discovered and numerous strategies have been utilized to enhance the expression level of VHb in various hosts, which greatly promotes its applications in biotechnology. Thus, in this review, the new information regarding structure, function and expressional tactics for VHb is summarized to understand its latest applications and pave a new way for the future improvement of biosynthesis for other products.

Autoinduction of Vitreoscilla Hemoglobin Enhanced the Production of Syringomycin from Pseudomonas syringae HS191

Syringomycin is a cyclic lipodepsipeptide produced by strains of Pseudomonas syringae. The potent herbicidal and fungicidal activities of syringomycin make it a promising compound for fungiostasis and weed control. However, the production of syringomycin from the wild-type strains is low. The discoveries that Pseudomonas syringae is aerobic, and the syringomycin synthetase SyrB2 is an O2-dependent halogenase, led us to establish an autoinducible Vitreoscilla hemoglobin expression system for oxygen supply during fermentation, thereby increasing the yield of syringomycin. By employing the quorum sensing system for the expression of Vitreoscilla hemoglobin gene (vgb), we found that Pseudomonas syringae HS191 that expressed vgb, facilitated the cell growth and the general biomass. Furthermore, syringomycin bioassay showed that the fungal inhibition zones increased from 2.5 mm to 3.2 mm, and HPLC analysis confirmed that the expression of vgb resulted in a 71.1% increase in syringomycin production compared to the wild-type strain. The Vitreoscilla hemoglobin has been widely applied to fermentation optimization; however, in the case of Pseudomonas, increased oxygen supply is only beneficial during the stationary phase, while a high concentration of oxygen inhibited the cell propagation during the logarithmic phase. Here we report the autoinduction of Vitreoscilla hemoglobin by engineering the quorum-sensing system. This synthetic circuit significantly improved the syringomycin production. The Vitreoscilla hemoglobin-autoinduction system not only caters to the dynamic oxygen demand but also avoids inducer supplementation.

Environment-friendly and efficient synthesis of 2-aminobenzoxazoles and 2-aminobenzothiazoles catalyzed by Vitreoscilla hemoglobin incorporating a cobalt porphyrin cofactor

In this work, an environment-friendly and efficient artificial Vitreoscilla hemoglobin (VHb) for the synthesis of 2-aminobenzoxazoles and 2-aminobenzothiazoles has been reported. We demonstrate an expression-based porphyrin substitution strategy to produce...