CgAS, a gene encoding anthranilic acid synthase, contributes to tryptophan biosynthesis and enhanced chaetoglobosin A production in Chaetomium globosum W7

Abstract

Chaetoglobosin A (cheA) is a complex indole alkaloid exhibiting preferential cytotoxicity against plant pathogens, parasites, and tumor cells. However, the limited production and high synthesis costs of cheA impede its widespread application. Tryptophan serves as a precursor for cheA biosynthesis, and strategic modification of the expression of key genes represents a novel approach to enhance the target yield. Herein, CgAS, a gene encoding anthranilic acid synthase involved in tryptophan synthesis, was identified through bioinformatics analysis and overexpressed via a promoter optimization strategy in Chaetomium globosum W7. The AS1 and AS3 mutants, in which the CgAS gene was constitutively overexpressed under the control of promoter oliC, presented a significant increase in tryptophan accumulation. CgAS overexpression caused a dramatic increase in cheA production, reaching a maximum yield of 217.81 mg/L during the stationary phase, which was 3.73-fold higher than that noted in the wild-type strain. Interestingly, AS1 and AS3 mutants exhibited a substantial upregulation in the transcription levels of critical genes involved in cheA biosynthesis. Phenotypic characterization and metabolomic analysis indicated that tryptophan accumulation strengthened microbial nitrogen metabolism, which not only provided sufficient precursors for secondary metabolism, but also functioned as an essential energy source to accelerate fungal development and sporulation. These findings illustrate the impact of precursor accumulation on indole alkaloid biosynthesis and provide novel insights for optimizing the production of biopesticides and clinical drugs.