L. leaf powder promotes initiation of indigo reduction by inducing of rapid transition of the microbial community.

Water-insoluble indigo is solubilized by the reducing action of microorganisms which occurs during fermentation. In natural indigo fermentation, composted leaves of L. () are the raw material that has been used as both the indigo source and the bacterial inoculum. Ideally, indigo reduction occurs shortly after preparation of the fermentation vat. The time-to-reduction depends on the quality of the and the methods for preparation and management of the fermentation batch. We estimated the effect of adding L. leaf powder (LP) to indigo fermentation in two fermentations originally exhibiting either rapid or slow time-to-reduction (T- and D-, respectively). spp. (97.7%-98.4% similarities with ) were observed only in the LP-added T- fermentation liquor. They appeared from day 1 (0.7%) and increased to 24.4% on day 6, and their presence was related to indigo reduction. Differences in functional ratio between LP-added and its control batches revealed enhancement of pathways related to reconstitution of cellular functions and substrate metabolisms, to all of which spp. contributed intensively. In D- batch, appearance of bacteria necessary to initiate indigo reduction (principally /) was comparatively slower. LP promotes earlier indigo reduction in both T- and D--based batches, owing to its promotion of microbiota transition. The effect of the LP was intensified from day 1 to day 2 in both using batches according to the assumed function of the microbiota. The initial effect of LP on the T- batches was more intense than that in the D- batches and was continued until day 3, while the duration in the T- batches was continued until day 5. Based on these observations, we propose that the LP functions through its phytochemicals that eliminate oxygen, stimulate the microbiota, and accelerate its transitional changes toward a suitable function that opens the pathway for the extracellular electron transfer using carbohydrates as a substrate.