Enhanced production of total flavones and exopolysaccharides via Vitreoscilla hemoglobin biosynthesis in Phellinus igniarius

The Vitreoscilla hemoglobin gene (vgb) was expressed by chromosomal integration in Phellinus igniarius to alleviate oxygen limitation and improve metabolites yields during submerged fermentation. Firstly, an expression vector containing vgb was constructed, and transformed into protoplast from P. igniarius. Carbon monoxide difference spectrum absorbance assay showed that vgb was successfully expressed and had biological activity. In shake flasks, the vgb expression enhanced dry mycelial weight 1.32-fold and increased total flavones and exopolysaccharides production 1.78- and 1.33-fold, respectively. When P. igniarius (vgb+) and P. igniarius (vgb−) strains were cultured in bioreactor, Vitreoscilla hemoglobin in P. igniarius promoted the mycelia growth from 5.40 to 10.90 g/L and stimulated total flavones and exopolysaccharides synthesis; their maximum productions reached to 11.43 and 1.33 g/L. Furthermore, compared to P. igniarius (vgb−), the acetic acid accumulation in P. igniarius (vgb+) cultures decreased from 1.54 and 1.78 to 1.19 and 1.27 g/L in flask and bioreactor, respectively.