Changes in the taxonomic and functional structures of microbial communities during vegetable waste mixed silage fermentation.

ABSTRACT

Silage fermentation, a sustainable method of using vegetable waste resources, is a complex process driven by a variety of microorganisms. We used lettuce waste as the main raw material for silage, analyzed changes in the physicochemical characteristics and bacterial community composition of silage over a 60-day fermentation period, identified differentially abundant taxa, predicted the functional profiles of bacterial communities, and determined the associated effects on the quality of silage. The largest changes occurred during the early stages of silage fermentation. Changes in the physicochemical characteristics included a decrease in pH and an increase in the ammonia nitrogen to total nitrogen ratio and lactic acid content. The number of lactic acid bacteria (LAB) increased, while molds, yeasts, and aerobic bacteria decreased. The bacterial communities and their predicted functions on day 0 were different from those on day 7 to day 60. The relative abundances of phylum Firmicutes and genus Lactobacillus increased. Nitrite and nitrate ammonification were more prevalent after day 0. The differences in the predicted functions were associated with differences in pH and amino acid, protein, carbohydrate, NH3-N, ether extract, and crude ash contents.