Microbial community structure and transformation of indoles in soaking and fermentation of Indigo Naturalis

Abstract

The soaking and fermentation of Baphicacanthus cusia( Nees),the important intermediate link of Indigo Naturalis processing,facilitates the synthesis of indigo and indirubin precursors and the dissolution of endogenous enzymes and other effective components,while the role of microorganisms in the fermentation is ignored. The present study investigated the changes of microbial community structure in Indigo Naturalis processing based on 16 S amplicon sequencing and bioinformatics. Meanwhile,the contents of indigo,indirubin,isatin,tryptanthrin,indole glycoside,etc. were determined to explore the correlation between the microorganisms and the alterations of the main components. As demonstrated by the results,the microbial diversity decreased gradually with the fermentation,which bottomed out after the addition of lime. Proteobacteria,Bacteroidetes,and Firmicutes were the main dominant communities in the fermentation. The relative abundance of Proteobacteria declined gradually with the prolongation of fermentation time,and to the lowest level after the addition of lime. The relative abundance of Firmicutes increased,and that of Bacteroidetes decreased first and then increased. The contents of effective substances in Indigo Naturalis also showed different variation tendencies. As fermentation went on,indole glycoside decreased gradually; indigo first increased and then decreased; indirubin and isatin first decreased and then increased; tryptanthrin gradually increased. Those changes were presumedly related to the roles of microorganisms in the synthesis of different components. This study preliminarily clarified the important role of microorganisms in the soaking and fermentation and provided a scientific basis for the control of Indigo Naturalis processing and the preparation of high-quality Indigo Naturalis.