Specific inhibition of Streptococcus bovis by endolysin LyJH307 supplementation shifts the rumen microbiota and metabolic pathways related to carbohydrate metabolism

Abstract Background: Ruminal acidosis negatively affects the animal production and performances of high-performance cattle by abnormal balancing of the rumen microbiota, which caused significant economic damage to farmers. Endolysins, the bacteriophage-originated peptidoglycan hydrolases, are a promising replacement of antibiotics due to their immediate lytic activity and no evidence of antibiotic resistance. The objectives of this study were to investigate the lytic activity of Streptococcus bovis specific endolysin LyJH307 against S. bovis and explore changes in rumen fermentation and microbiota in an in vitro system. Treatments consisted of corn grain with protein elution buffer and corn grain with endolysin LyJH307 (LyJH307, 0.2% of dietary dry matter). The rumen bacterial community was analyzed using 16S rRNA amplicon sequencing, followed by the prediction of microbial functional features by using PICRUSt2.Results: Endolysin LyJH307 supplementation at 6 h incubation time markedly decreased the absolute abundance of S. bovis (approximately 70%) and increased ruminal pH at the end of the incubation. There were no significant changes in gas production, in vitro dry matter degradability, and total volatile fatty acid production. The acetate proportion was significantly increased after LyJH307 addition, whereas propionate was decreased, thereby inducing an increase of acetate to propionate ratio in LyJH307. LyJH307 supplementation increased D-lactate without any change in L-lactate concentration. Among the alpha diversity indices, there were no significant differences in Shannon’s index, Simpson’s index, Chao1 estimates, and evenness. Based on Bray-Curtis dissimilarity matrices, the LyJH307 affected the overall shift in ruminal microbiota. Endolysin LyJH307 supplementation induced an increase of 11 genera containing Lachnoclostridium, WCHB1-41, unclassified genus Selenomonadaceae, Paraprevotella, vadinBE97, Ruminococcus gauvreauii group, Lactobacillus, Anaerorhabdus furcosa group, Victivallaceae, Desulfuromonadaceae, and Sediminispirochaeta. The predicted functional features represented by the Kyoto Encyclopedia of Genes and Genomes pathways were changed by LyJH307 toward a decrease of carbohydrate metabolism.Conclusions: Endolysin LyJH307 caused a reduction of S. bovis and an increase of ruminal pH with concomitant shifts in minor rumen microbiota and its metabolic pathways related to carbohydrate metabolism. This study provides the first insight into the availability of endolysin as a specific modulator for rumen and shows the possibility of endolysin degradation by rumen microbiota.