Tannin Tolerance in Lactic Acid Bacteria Modulates Whole-Plant Sorghum Silage Quality and In Vitro Methane Mitigation

Although tannins generally inhibit the growth of lactic acid bacteria, different strains vary significantly in their tolerance to this inhibitory effect. However, it remains unclear whether the differences in tannin tolerance among various lactic acid bacteria (LAB) lead to variations in the fermentation outcomes during the silage process and in vitro fermentation. Therefore, this study investigated the correlation between the fermentation effects of LAB with varying tannin tolerances and the tannin content of sorghum. Four LAB strains (Lactococcus garvieae, LG; Lactococcus lactis, LL; Lactiplantibacillus plantarum, LP; Pediococcus pentosaceus, PP) were selected and identified from whole sorghum and mulberry leaves, and their tannin tolerance was assessed. The results demonstrated that LG exhibited the highest tolerance to sorghum tannins, followed by LL and LP, while PP displayed the lowest tolerance. Upon addition of LAB to whole sorghum for silage, LG showed the most effective ability to lower pH, reduce ammonia nitrogen content, decrease neutral detergent fiber content, diminish microbial diversity, and enhance the abundance of firmicutes. Concurrently, during in vitro fermentation, they significantly reduced rumen fluid pH and suppressed gas emissions (CH4, CO2). Conversely, PP performed poorly across all parameters. These findings suggest that the fermentation effects of LAB on sorghum silage are closely related to their tannin tolerance.