Mammalian Gut Microbes and Plant Toxins
Desert Woodrat trapped in southern Utah
With every meal, herbivores eat a diet high in indigestible fiber and low in protein. To overcome these challenges, many herbivores house symbiotic microbes that ferment fiber and synthesize amino acids. However, many plants also produce toxic compounds that dissuade herbivores from eating them. For almost 40 years it has been hypothesized that mammalian herbivores might also harbor microbes that help to detoxify their diets. However, this idea has never been sufficiently tested.
To test this, I studied the Desert Woodrat (Neotoma lepida), which specializes on a toxic shrub, creosote bush. This plant produces a resin that is rich in carcinogenic phenolics. Every day woodrats consume enough enough creosote toxins to kill a lab mouse. Woodrats are also interesting in that they have a semi-segmented stomach, and maintain a foregut chamber that houses a dense and diverse microbial community. We hypothesize that this chamber may be important for early detoxification before compounds would be absorbed in the small intestine. Thus, they represent an excellent study system in which to study the evolution of microbial interactions that allow herbivores to deal with plant toxins.
A review article summarizing the findings of this research can be found here: [Link].
Specifically, this work has resulted in the following findings:
1. Woodrats increase activities of digestive enzymes in response to plant toxins to overcome their inhibitory properties [PDF].
2. Rodent species that have evolved stomach segmentation maintain higher stomach pH, which may allow for increased microbial growth [Link].
3. The natural gut microbial communities of woodrats are retained upon entrance into captivity [Link].
4. Woodrats house a dense and active foregut microbial community [Link].
5. Woodrats that specialize on cactus maintain a diverse community of microbes that degrade oxalate, a type of toxin [Link].
6. Previous experience with plant toxins determines the response of the gut microbial community to such toxins [PDF].
7. The gut microbiota play a large role in allowing mammalian herbivores to consume plant toxins [PDF].