Author
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Weimer, Paul |
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Submitted to: Frontiers in Microbiology
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 3/6/2015 Publication Date: N/A Citation: N/A Interpretive Summary: Attempts to modify the rumen community by introducing microbial strains have generally been unsuccessful because introduced strains cannot compete successfully with the established members of the community. In almost all cases, successful introductions require that the introduced strain perform a beneficial function that is not carried out by the existing community members. In cases where introduced strains must compete with community members, the introduced strains must be selected under rumen-like conditions, and introduced under conditions that temporarily suppress these members. By providing specific examples of why introductions succeed or fail, this work will be of use to scientists working to develop probiotic strains for use in ruminant animals. Technical Abstract: The ruminal microbial community is remarkably diverse, containing hundreds of different bacterial and archaeal species, plus many species of fungi and protozoa. Molecular studies have identified a “core microbiome” dominated by members of the phyla Firmicutes and Bacteroidetes, but also containing many other taxa. Because of its many types of potential interactions among community members and our ability to control inputs, the rumen provides an ideal laboratory for studies on microbial ecology and the demonstration of important ecological principles. In particular, the microbial community demonstrates both redundancy (overlap of function among multiple species) and resilience (resistance to, and capacity to recover from, perturbation). These twin properties provide remarkable stability that maintains digestive function for the host across a range of feeding and management conditions. However, they also provide a challenge to engineering the rumen for improved function (e.g., decreased methane production). Direct ruminal dosing or feeding of probiotic strains often fails to establish the added strains, due to intensive competition and amensalism from the indigenous residents that are well-adapted to the historical conditions within each rumen. Exceptions come primarily in the form of introduced strains that can fill otherwise unoccupied niches, as in the case of specialist bacteria that degrade phytotoxins such as mimosine or oxalate. An additional complicating factor in manipulating the ruminal fermentation is the individuality or host specificity of the microbiota in which individual animals contain a particular community whose species composition is capable of reconstituting itself, even following a near-total exchange of ruminal contents from another herdmate maintained on the same diet. Elucidation of the interactions between the microbial community and the individual host that establish and maintain this specificity may provide insights into why individual hosts vary in production metrics (e.g., feed efficiency or milk fat synthesis), and how to improve herd performance (e.g., by grouping cows for application of different feeding and management regimens). |
