Changes in the taxonomic and functional structure of microbial communities during vegetable waste mixed silage fermentation
Silage fermentation, a sustainable way to use 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 physico-chemical characteristics and bacterial community composition of silage over a 60-day fermentation, identified differentially abundant taxa, predicted the functional profiles of bacterial communities, and determined the associated effects on the quality of silage. The biggest changes occurred in the early stage of silage fermentation. Changes in the physico-chemical characteristics included a decrease in pH and increases in ammonia nitrogen to total nitrogen ratio and lactic acid content. The numbers of lactic acid bacteria (LAB) increased and molds, yeasts and aerobic bacteria decreased. The bacterial communities and their predicted functions on day 0 were clearly different from those on day 7 to day 60. The relative abundances of phylum Firmicutes and genus Lactobacillus increased. Nitrite ammonification 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.