AUTHOR=Dong Chenyang , Wei Manlin , Ju Ji , Du Liu , Zhang Runze , Xiao Ming , Zheng Yongjie , Bao Hailin , Bao Meili 

TITLE=Effects of guanidinoacetic acid on in vitro rumen fermentation and microflora structure and predicted gene function

JOURNAL=Frontiers in Microbiology

VOLUME=14

YEAR=2024

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2023.1285466

DOI=10.3389/fmicb.2023.1285466

ISSN=1664-302X

ABSTRACT=<p>The fermentation substrate was supplemented with 0% guanidinoacetic acid (GAA) (control group, CON), 0.2% GAA (GAA02), 0.4% GAA (GAA04), 0.6% GAA (GAA06) and 0.8% GAA (GAA08) for 48 h of <italic>in vitro</italic> fermentation. Gas production was recorded at 2, 4, 6, 8, 12, 24, 36, and 48 h of fermentation. The gas was collected, and the proportions (%, v/v) of H<sub>2</sub>, CH<sub>4</sub> and CO<sub>2</sub> were determined. The rumen fermentation parameters, including pH, ammonia nitrogen (NH<sub>3</sub>-N), microbial protein (MCP) and volatile fatty acids (VFAs), were also determined. Furthermore, the bacterial community structure was analyzed through 16S rRNA high-throughput sequencing. The gene functions were predicted using PICRUSt1 according to the Kyoto Encyclopedia of Genes and Genomes (KEGG). The results showed that with the increase in GAA supplementation levels, the MCP and the concentration of rumen propionate were significantly increased, while the concentration of isovalerate was significantly decreased (<italic>p</italic> &lt; 0.05). The results of microbial diversity and composition showed that the Shannon index was significantly decreased by supplementation with GAA at different levels (<italic>p</italic> &lt; 0.05), but the relative abundance of <italic>norank_f_F082</italic> and <italic>Papillibacter</italic> in the GAA06 group was significantly increased (<italic>p</italic> &lt; 0.05). Especially in group GAA08, the relative abundances of Bacteroidota, <italic>Prevotella</italic> and <italic>Prevotellaceae_UCG-001</italic> were significantly increased (<italic>p</italic> &lt; 0.05). The results of gene function prediction showed that the relative abundances of the functions of flagellar assembly, bacterial chemotaxis, plant–pathogen interaction, mismatch repair and nucleotide excision repair were significantly decreased (<italic>p</italic> &lt; 0.05), but the relative abundances of bile secretion and protein digestion and absorption were significantly increased (<italic>p</italic> &lt; 0.05). In conclusion, supplementation with 0.8% GAA enhanced <italic>in vitro</italic> rumen fermentation parameters, increased the relative abundance of <italic>Prevotella</italic> and <italic>Prevotellaceae_UCG-001</italic> in the rumen, and increased the metabolic pathways of bile secretion and protein digestion and absorption.</p>