Recycling of Chinese herb residues by endophytic and probiotic fungus Aspergillus cristatus CB10002 for the production of medicinal valuable anthraquinones

BACKGROUND: The global prevalence of traditional Chinese medicine stimulates the prosperous development of herb medicines, but the annual generation of massive herb residues becomes big issues about environmental pollution and waste of resources. Microbes play important roles in the circulation of substances in nature, and endophytes represent an underexplored microbial resource possessing the unique symbiotic relationship with plants, not only for discovery of secondary metabolites, but also for potential green recycling of herb residues. RESULTS: The recycling capacities of several endophytic strains were respectively evaluated via solid state fermentation with herb residues of commercial Huazhenghuisheng oral-liquid (HOL). Among them, Aspergillus cristatus CB10002, a probiotic fungus isolated from Chinese Fu-brick tea, was competent to recycle HOL residues for the production of medicinal valuable anthraquinones, in which four of them, especially citreorosein with significant anti-obesity activity, were first discovered in A. cristatus. Subsequent quantitative analysis showed that about 2.0 mg/g citreorosein and 7.5 mg/g total anthraquinones could be obtained after 35-day fermentation, which was very competitive and economically beneficial. Further nutritional comparisons also revealed that the recycling process indeed ameliorated the nutrients of HOL residues, and thus proposed a possibility to directly dispose the final leftovers as a compost organic fertilizer. CONCLUSIONS: The endophytic and probiotic fungus A. cristatus CB10002 isolated from Chinese Fu-brick tea was screened out to effectively reutilize HOL residues for the production of nine medicinal valuable anthraquinones, whose biosynthesis may be regulated by the induction of HOL residues. The competitive yields of these anthraquinones, as well as the certain composting properties of final leftovers, have made the microbial recycling of HOL residues economically beneficial. Our work demonstrated a promising applied potential of A. cristatus in reutilization of herb residues, and provided a practical strategy for sustainable and value-added microbial recycling of herb residues. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1186/s12934-019-1150-9) contains supplementary material, which is available to authorized users.