Bacterial diversity dynamics in rumen epithelium of wethers fed forage and mixed concentrate forage diets

Cereal-rich diets used in ruminant intensive production can affect the physiology of the rumen wall but little is known about the changes induced to the epimural bacterial community. Dynamics in epimural bacteria was monitored by PCR-DGGE on four wethers fed forage for 20 weeks (constant diet) and on four wethers fed successively forage, a high concentrate diet (65% wheat) and forage for 4, 8 and 8 weeks, respectively (variable diet group). In the constant diet group, no changes were observed throughout time. In contrast, in the variable diet group, the community tended to differ between high concentrate and forage samples (P=0.06). For both groups, the structure of the community was strongly associated to individual hosts (P=0.001). This difference between individuals could have masked the effect of cereal on the variable diet group. To get more information on the phylotypes present, 120 16S rDNA gene clones were sequenced from the rumen epithelium of a wether fed forage and cereal-rich diets. Firmicutes, Bacteroidetes, and Proteobacteria were the predominant phyla but the bacterial types detected were in general different from those commonly found in rumen contents with a high proportion of Proteobacteria (14%) in the rumen epithelium. In the forage periods, Firmicutes represented nearly 50% of the total epimural community and Bacteroidetes were about 33%, while in the concentrate-rich diet period these percentages were inversed (P<0.05). Clone libraries seemed more sensitive than PCR-DGGE to study the bacteria attached to the rumen epithelium. The role of epimural bacteria on ruminant's health needs further investigation.