Enhanced Butanol Production Using Non-ionic Surfactant-Based Extractive Fermentation: Effect of Substrates and Immobilization of Cell

Surfactant-mediated bio-manufacture: A unique strategy for promoting microbial biochemicals production

Biochemicals are widely used in the medicine and food industries and are more efficient and safer than synthetic chemicals. The amphipathic surfactants can interact with the microorganisms and embed the extracellular metabolites, which induce microbial metabolites secretion and biosynthesis, performing an attractive prospect of promoting the biochemical production. However, the commonness and differences of surfactant-mediated bio-manufacture in various fields are largely unexplored. Accordingly, this review comprehensively summarized the properties of surfactants, different application scenarios of surfactant-meditated bio-manufacture, and the mechanism of surfactants increasing metabolites production. Various biochemical productions such as pigments, amino acids, and alcohols could be enhanced using the cloud point and the micelles of surfactants. Besides, the amphiphilicity of surfactants also promoted the utilization of fermentation substrates, especially lignocellulose and waste sludge, by microorganisms, indirectly increasing the metabolites production. The increase in target metabolites production was attributed to the surfactants changing the permeability and composition of the cell membrane, hence improving the secretion ability of microorganisms. Moreover, surfactants could regulate the energy metabolism, the redox state and metabolic flow in microorganisms, which induced target metabolites synthesis. This review aimed to broaden the application fields of surfactants and provide novel insights into the production of microbial biochemicals.

Promotion of monacolin K production in Monascus extractive fermentation: the variation in fungal morphology and in the expression levels of biosynthetic gene clusters

BACKGROUND

Monacolin K, an important secondary metabolite of Monascus, possesses a cholesterol-lowering effect and is widely used in the manufacture of antihypertensive drugs. In the present study, we constructed an extractive fermentation system by adding non-ionic surfactant and acquired a high monacolin K yield. The mechanism was determined by examining both cell morphology and the transcription levels of the related mokA-I genes in the monacolin K biosynthetic gene cluster.

RESULTS

The monacolin K yield was effectively increased to 539.59 mg L^-1 during extraction, which was an increase of 386.16% compared to that in the control group fermentation. The non-ionic surfactant showed good biocompatibility with Monascus. Electron scanning microscopy revealed alterations in the morphology of Monascus. The loosened mycelial structure and increased number of cell surface wrinkles were found to be related to the increased cell-membrane permeability and extracellular accumulation of monacolin K. Gene expression levels were measured via a quantitative reverse transciptase-polymerase chain reaction. By contrast, in the control group, mokA, mokB, mokC, mokD and mokF showed higher-level and longer-term expression in the extractive fermentation group, whereas mokE and mokG did not present a similar trend. The expression levels of mokH and mokI, encoding a transcription factor and efflux pump, respectively, were also higher than the control levels.

CONCLUSION

The addition of a non-ionic surfactant to Monascus fermentation effectively increases the yield of monacolin K by transforming the fungus morphology and promoting the expression of monacolin K biosynthesis genes. © 2021 Society of Chemical Industry.