A survey of fermentation parameters, bacterial community compositions and their metabolic pathways during the ensiling of sorghum.

Abstract

To investigate the fermentative products, bacterial community compositions and their metabolic pathways of sorghum (Sorghum dochna Snowden) during ensiling. Sorghum was harvested at soft dough stage and ensiled in laboratory-scale silos (10L capacity). Triplicate silos were sampled after 1, 3, 7, 15, 30 and 60days of ensiling, respectively. The bacterial communities on day 3 and 60 were assessed through high-throughput sequencing technology, and 16S rRNA gene-predicted functional profiles were analysed according to the KEGG (Kyoto Encyclopedia of Genes and Genomes) using Tax4Fun. The sorghum silages had high lactic acid (~85.4gkg-1 dry matter [DM]) contents, and low pH (~3.90), butyric acid (~1.27gkg-1 DM) and ammonia nitrogen (~86.3gkg-1 total nitrogen [TN]) contents. During the ensiling, glucose was the first fermentable substrate, and the contents of xylose and arabinose were increased. The dominant genus Lactococcus on day 3 was replaced by Lactobacillus on day 60. The metabolism of amino acid, energy, cofactors and vitamins was inhibited, whilst the metabolism of nucleotide and carbohydrate was promoted after ensiling. 1-Phosphofructokinase and pyruvate kinase of bacterial community played important roles in stimulating the lactic acid fermentation. Knowledge about bacterial community dynamics and their metabolic pathways during sorghum ensiling is important for understanding the fermentative profiles and may promote the production of nutritious and stable sorghum silage. The high-throughput sequencing technology combined with 16S rRNA gene-predicted functional analyses revealed the differences in silages not only for distinct bacterial community but also for specific functional metabolites. This could provide some new insights into bacterial community and functional profiles to further improve the silage quality.