Rumen ecological distribution of Pichia yeasts and their effects on rumen fermentation and microbial community

Yeast supplementation has been widely studied to enhance rumen fermentation and feed efficiency, yet developing efficient yeasts adapted to the rumen environment remains a challenge. In this study, two rumen-derived Pichia strains (Pichia membranifaciens M12 and Pichia kudriavzevii Y4) were evaluated using in vitro rumen fermentation experiments, including a control and three supplementation groups (2 × 10⁵, 2 × 10⁶, and 2 × 10⁷ CFU/mL) for each strain. Results indicated that the two strains did not affect pH but significantly reduced concentrations of ammonium nitrogen (NH₃-N) and microbial crude protein (MCP). At 24 h, NH₃-N decreased by up to 13.3% and MCP by 18.5%, while at 48 h, NH₃-N showed a reduction of up to 22.0% and MCP decreased by up to 5.7%. P. membranifaciens significantly increased the concentration of total volatile fatty acids by 15.4% and elevated the proportions of acetate and propionate at 48 h. Microbial community analysis revealed that these shifts in fermentation parameters were associated with an altered bacterial community structure. Specifically, P. membranifaciens enriched cellulolytic bacteria (Ruminococcus), while reducing amylolytic and proteolytic taxa (Prevotella), and promoted the propionate‑producer (Succiniclasticum). These findings suggested that P. membranifaciens has the potential to influence rumen microbiota. Further examination of the in vivo prevalence of Pichia yeasts species via ITS (n = 72; average parity 2.8 ± 1.1) revealed a lower prevalence and relative abundance for P. membranifaciens compared to P. kudriavzevii. Metagenomic analysis (n = 8; average parity 2.7 ± 0.9) detected both species at low abundances. Overall, this study indicated that rumen-derived Pichia yeasts have the capacity to modulate rumen fermentation, with P. membranifaciens warranting further in vivo evaluation.