Differences in Ureolytic Bacterial Composition between the Rumen Digesta and Rumen Wall Based onureCGene Classification.
Ureolytic bacteria are key organisms in the rumen producing urease enzymes to catalyze the breakdown of urea to ammonia for the synthesis of microbial protein. However, little is known about the diversity and distribution of rumen ureolytic microorganisms. The urease gene (ureC) has been the target gene of choice for analysis of the urea-degrading microorganisms in various environments. In this study, we investigated the predominantureCgenes 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. A control group (n= 3) were fed a total mixed ration without urea and the treatment group (n= 3) were fed rations plus 180 g urea per cow per day at three separate times. Rumen bacterial samples from liquid and solid digesta and rumen wall fractions were collected forureCgene amplification and sequencing using Miseq. The wall-adherent bacteria (WAB) had a distinct ureolytic bacterial profile compared to the solid-adherent bacteria (SAB) and liquid-associated bacteria (LAB) but more than 55% of theureCsequences did not affiliate with any known taxonomically assigned urease genes. Diversity analysis of theureCgenes showed that the Shannon and Chao1 indices for the rumen WAB was lower than those observed for the SAB and LAB (P< 0.01). The most abundantureCgenes were affiliated with Methylococcaceae, Clostridiaceae, Paenibacillaceae, Helicobacteraceae, and Methylophilaceae families. Compared with the rumen LAB and SAB, relative abundance of the OTUs affiliated withMethylophilusandMarinobactergenera were significantly higher (P< 0.05) in the WAB. Supplementation with urea did not alter the composition of the detected ureolytic bacteria. This study has identified significant populations of ureolytic WAB representing genera that have not been recognized or studied previously in the rumen. The taxonomic classification of rumenureCgenes in the dairy cow indicates that the majority of ureolytic bacteria are yet to be identified. This survey has expanded our knowledge ofureCgene information relating to the rumen ureolytic microbial community, and provides a basis for obtaining regulatory targets of ureolytic bacteria to moderate urea hydrolysis in the rumen.
State Key Laboratory of Animal Nutrition, Institute of Animal Science, Chinese Academy of Agricultural SciencesBeijing, China; Precision Livestock and Nutrition Unit, Gembloux Agro-Bio Tech, University of LiègeGembloux, Belgium; Laboratory of Quality and Safety Risk Assessment for Dairy Products of Ministry of Agriculture (Beijing), Institute of Animal Science, Chinese Academy of Agricultural SciencesBeijing, China.
Di
D
Jin
State Key Laboratory of Animal Nutrition, Institute of Animal Science, Chinese Academy of Agricultural SciencesBeijing, China; Laboratory of Quality and Safety Risk Assessment for Dairy Products of Ministry of Agriculture (Beijing), Institute of Animal Science, Chinese Academy of Agricultural SciencesBeijing, China.
Shengguo
S
Zhao
State Key Laboratory of Animal Nutrition, Institute of Animal Science, Chinese Academy of Agricultural SciencesBeijing, China; Laboratory of Quality and Safety Risk Assessment for Dairy Products of Ministry of Agriculture (Beijing), Institute of Animal Science, Chinese Academy of Agricultural SciencesBeijing, China.
Nan
N
Zheng
State Key Laboratory of Animal Nutrition, Institute of Animal Science, Chinese Academy of Agricultural Sciences Beijing, China.
Dengpan
D
Bu
Precision Livestock and Nutrition Unit, Gembloux Agro-Bio Tech, University of Liège Gembloux, Belgium.
Yves
Y
Beckers
Commonwealth Scientific and Industrial Research Organisation, Queensland Bioscience Precinct, St. Lucia QLD, Australia.
Stuart E
SE
Denman
Commonwealth Scientific and Industrial Research Organisation, Queensland Bioscience Precinct, St. Lucia QLD, Australia.
Christopher S
CS
McSweeney
State Key Laboratory of Animal Nutrition, Institute of Animal Science, Chinese Academy of Agricultural SciencesBeijing, China; Laboratory of Quality and Safety Risk Assessment for Dairy Products of Ministry of Agriculture (Beijing), Institute of Animal Science, Chinese Academy of Agricultural SciencesBeijing, China.
Jiaqi
J
Wang
difference; rumen digesta; rumen wall; ureC gene; ureolytic bacteria