Lignocellulolytic microbiomes orchestrating degradation cascades in the rumen of dairy cattle and their diet-influenced key degradation phases

Dairy cattle (Bos taurus) can convert lignocellulosic biomass into milk efficiently via their rumen symbiotic microbiota. However, the mechanisms by which the rumen microbiota of cows mediate the degradation cascades of lignocellulose and the specific stages primarily affected by dietary interventions remain unclear. Herein, 244 rumen metagenome samples from Holstein cows were used, identifying 1353 high-quality microbial metagenome-assembled genomes (MAGs) responsible for the degradation cascades of lignocellulose. It was revealed that Fibrobacter spp. and Ruminococcus spp. exhibited numerous endo-/exo-glucanases with accessory non-catalytic multi-carbohydrate binding modules for highly efficient cellulolytic abilities. Prevotella spp. and Cryptobacteroides spp. developed diverse polysaccharide utilization loci (PULs) to tackle the main and side chains of hemicellulose, particularly acetylxylan esterase-contained PULs. Notably, novel and potential lignocellulolytic microbiomes were identified in the rumen of dairy cattle, such as Hallerella spp., Sodaliphilus spp., and Mageeibacillus spp. Through in vivo diet intervention and in sacco rumen incubation, it was discovered that high-grain diets primarily affected Prevotella spp., leading to a reduction in the initial degradation of amorphous regions in lignocellulose. Therefore, the present findings systematically illustrate the orchestrated enzymatic strategies of the cow rumen microbiota for the degradation cascades of lignocellulose, contributing to the dietary regulation of dairy cattle.