|EMERSON, ELIANNA - University Of Wisconsin|
Submitted to: Applied Microbiology and Biotechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/22/2017
Publication Date: 4/26/2017
Citation: Emerson, E.L., Weimer, P.J. 2017. Fermentation of model hemicelluloses by Prevotella strains and Butyrivibrio fibrisolvens in pure culture and in ruminal enrichment cultures. Applied Microbiology and Biotechnology. 101:4269-4278.
Interpretive Summary: Hemicelluloses are, after cellulose, the most abundant component of forages, but their digestion in the rumen is poorly understood. We compared several rumen bacterial species for their ability to ferment different hemicelluloses in pure culture and in mixed cultures with other rumen bacteria. Members of the Prevotella group, the most abundant group in the rumen, digested hemicellulose poorly in pure culture, but competed well for hemicellulose in the presence of other rumen bacteria. This suggests that they benefit from positive interactions with other species and may be the most important hemicellulose degraders in the rumen. The results will be of use in mathematical modeling of the rumen fermentation, and in designing strategies to improve fiber digestion in the rumen.
Technical Abstract: Hemicelluloses are major components of plant biomass, but their fermentation in the rumens of cattle and other ruminants is poorly understood. We compared four species of the ruminally dominant genus Prevotella and the well-known hemicellulose utilizer, Butyrivibrio fibrisolvens, with respect to degradation of several isolated hemicelluloses (xylan, glucomannan and xyloglucan). We also used Illumina sequencing of 16S rRNA genes to examine the relative proportions of Prevotella and Butyrivibrio in hemicellulose-fed enrichment cultures inoculated from ruminal contents of dairy cattle fed a total mixed ration (TMR) rich in hemicelluloses. Results confirmed the xylan fermentation and butyrate production abilities of B. fibrisolvens; however, despite their reputation as generalist fermenters, the Prevotella strains poorly fermented these hemicelluloses. The Prevotella strains exhibited dramatic differences in the fermentative end products. Prevotella was much less abundant in mixed bacterial enrichment cultures fed the same TMR than in the ruminal inoculum, but Prevotella was again the most abundant genus in enrichment cultures fed xylans. By contrast, glucomannan fermentations were dominated by Streptococcus species. Genera known for hemicellulose degradation (Butyrivibrio, Ruminococcus, and Fibrobacter) were not significantly enriched on these hemicelluloses, suggesting that Prevotella strains compete more effectively for hemicellulose within the complex microbial community. Differences in community composition between in vitro hemicellulose enrichments and inoculum samples emerged at every phylogenetic level, suggesting that in vitro conditions provide unique selective pressure on the bacterial community, and that ruminal bacteria exhibit specialization with respect to their hemicellulose utilization abilities.