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1608
Metagenomic census of predominant ureC genes of ureolytic bacteria in the rumen of dairy cows
Rumen ureolytic bacteria elaborates urease to break down urea to ammonia for the synthesis of microbial protein, yet little is known about the diversity and distribution of rumen ureolytic microorganisms. The urease ureC gene has been chosen as the target gene for analysis of the urea-degrading microorganisms in various environments. This research investigated the predominant ureC genes of the ureolytic bacteria in the rumen of dairy cows using high-throughput sequencing. Six dairy cows with rumen fistulas were assigned to a two period cross-over trial. One group (Ctrl; n=3) were fed the diet without urea and the other (Urea; n=3) were fed rations plus 180 g urea per cow per day at three separate times. Rumen bacterial samples from liquid, solid and wall fractions were collected for ureC gene amplification and sequencing using Miseq. Results showed that supplementation of urea did not change the rumen ureC gene abundance, while the wall-adherent bacteria (WAB) revealed distinct ureolytic bacterial profile compared with solid-adherent bacteria (SAB) and liquid-associated bacteria (LAB). The ureC gene diversity and richness of rumen WAB was lower than that in the SAB and LAB (P < 0.05). The rumen predominant ureC gene operational taxonomic units (OTUs) were gathered in cluster Ⅱ, Ⅳ and Ⅵ. OTU 5, 6, 15, 18, 12, 27, 25 in the WAB, OTU 3, 4, 1 in the LAB, and OTU 13, 19, 21 in the SAB were predominant in each fraction respectively. Most of the predominant OTUs showed low similarity (72-91 %) to the known rumen bacteria. The results suggested that the rumen of dairy cows harbors plenty of unidentified ureolytic bacteria. This survey contributes new data to existing ureCgene information relating to the ureolytic microbial community in ruminants, and provides basis for obtaining the regulation targets of ureolytic bacteria to mitigate urea hydrolysis in the rumen.