Metagenomic analysis revealed significant changes in cattle rectum microbiome and antimicrobial resistome under fescue toxicosis

TL;DR

This study used metagenomic sequencing to reveal significant changes in cattle rectum microbiome and antimicrobial resistance under fescue toxicosis, identifying potential biomarkers and functional shifts associated with the condition.

Contribution

It provides the first comprehensive metagenomic analysis of microbiome and resistome changes in cattle under fescue toxicosis, highlighting Ruminococcaceae bacterium P7 as a potential biomarker.

Findings

Microbial diversity decreased significantly after toxicosis.

Ruminococcaceae bacterium P7 increased 16-fold in feces.

Functional pathways shifted from energy metabolism to antimicrobial resistance.

Abstract

Fescue toxicity causes reduced growth and reproductive issues in cattle grazing endophyte-infected tall fescue. To characterize the gut microbiota and its response to fescue toxicosis, we collected fecal samples before and after a 30-days toxic fescue seeds supplementation from eight Angus Simmental pregnant cows and heifers. We sequenced the 16 metagenomes using the whole-genome shotgun approach and generated 157 Gbp of metagenomic sequences. Through de novo assembly and annotation, we obtained a 13.1 Gbp reference contig assembly and identified 22 million microbial genes for cattle rectum microbiota. We discovered a significant reduction of microbial diversity after toxic seed treatment (P<0.01), suggesting dysbiosis of the microbiome. Six bacterial families and 31 species are significantly increased in the fecal microbiota (P-adj<0.05), including members of the top abundant rumen core taxa. This global elevation of rumen microbes in the rectum microbiota suggests a potential impairment of rumen microbiota under fescue toxicosis. Among these, Ruminococcaceae bacterium P7, an important species accounting for ~2% of rumen microbiota, was the most impacted with a 16-fold increase from 0.17% to 2.8% in feces (P<0.01). We hypothesized that rumen Ruminococcaceae bacterium P7 re-adapted to the large intestine environment under toxic fescue stress, causing this dramatic increase in abundance. Functional enrichment analysis revealed that the overrepresented pathways shifted from energy metabolism to antimicrobial resistance and DNA replication. In conclusion, we discovered dramatic microbiota alterations in composition, abundance, and functional capacities under fescue toxicosis, and our results suggest Ruminococcaceae bacterium P7 as a potential biomarker for fescue toxicosis management.