Increasing the heterologous production of spinosad in Streptomyces albus J1074 by regulating biosynthesis of its polyketide skeleton

Spinosyns are natural broad-spectrum biological insecticides with a double glycosylated polyketide structure that are produced by aerobic fermentation of the actinomycete,Saccharopolyspora spinosa.However,their large-scale overproduction is hindered by poorly understood bottlenecks in optimizing the original strain,and poor adaptability of the heterologous strain to the production of spinosyn.In this study,we genetically engineered heterologous spinosyn-producer Streptomyces albus J1074 and optimized the fermentation to improve the production of spinosad(spinosyn A and spinosyn D)based on our previous work.We systematically investigated the result of overexpressing polyketide synthase genes(spnA,B,C,D,E)using a constitutive promoter on the spinosad titer in S.albus J1074.The supply of polyketide synthase precursors was then increased to further improve spinosad production.Finally,increasing or replacing the carbon source of the culture medium resulted in a final spinosad titer of~70 mg/L,which is the highest titer of spinosad achieved in heterologous Streptomyces species.This research provides useful strategies for efficient heterologous production of natural products.

Conversion of the high-yield salinomycin producer Streptomyces albus BK3-25 into a surrogate host for polyketide production

An ideal surrogate host for heterologous production of various natural products is expected to have efficient nutrient utilization,fast growth,abundant precursors and energy supply,and a pronounced gene expression.Streptomyces albus BK3-25 is a high-yield industrial strain producing type-Ⅰ polyketide sahnomycin,with a unique ability of bean oil utilization.Its potential of being a surrogate host for heterologous production of PKS was engineered and evaluated herein.Firstly,introduction of a three-gene cassette for the biosynthesis of ethylmalonyl-CoA resulted in accumulation of ethylmalonyl-CoA precursor and sahnomycin,and subsequent deletion of the sahnomycin biosynthetic gene cluster resulted in a host with rich supplies of common polyketide precursors,including malonyl-CoA,methylmalonyl-CoA,and ethylmalonyl-CoA.Secondly,the energy and reducing force were measured,and the improved accumulation of ATP and NADPH was observed in the mutant.Furthermore,the strength of a series of selected endogenous promoters based on microarray data was assessed at different growth phases,and a strong constitutive promoter was identified,providing a useful tool for further engineered gene expression.Finally,the potential of the BK3-25 derived host ZXJ-6 was evaluated with the introduction of the actinorhodin biosynthetic gene cluster from Streptomyces coelicolor,and the heterologous production of actinorhodin was obtained.This work clearly indicated the potential of the high-yield sahnomycin producer as a surrogate host for heterologous production of polyketides,although more genetic manipulation should be conducted to streamline its performance.

Chemo-enzymatic synthesis of bioactive compounds from traditional Chinese medicine and medicinal plants

The production of bioactive compounds from traditional Chinese medicine and medicinal plants mainly depends on the extraction and separation from medicinal materials,which is time-consuming,laborious,and requires large amounts of medicinal resources.As the market demand for bioactive compounds increases,the shortage ofmedicinal resources tops the list.For a stable and sustainable supply of affordable bioactive compounds,it is necessary to optimize chemosynthetic and biosynthetic pathways.Although some progress has been made in chemocatalysis and biosynthesis,there are drawbacks and bottlenecks in current approaches.We hold the opinion that the combination of chemosynthesis and biosynthesis will be the key direction to efficiently produce bioactive compounds.Chemoenzymatic synthesis,a strategy that combines biosynthesis and chemosynthesis,is an alternative approach for the heterologous production of bioactive compounds.This paper reviews the recent advances in the chemo-enzymatic synthesis of bioactive compounds derived from traditional Chinese medicine and medicinal plants,highlights the potential application,and presents our perspectives for future research.