Contributions of Microbes in Vertebrate Gastrointestinal Tract to Production and Conservation of Nutrients

Abstract

The vertebrate gastrointestinal tract is populated by bacteria and, in some species, protozoa and fungi that can convert dietary and endogenous substrates into absorbable nutrients. Because of a neutral pH and longer digesta retention time, the largest bacterial populations are found in the hindgut or large intestine of mammals, birds, reptiles, and adult amphibians and in the foregut of a few mammals and at least one species of bird. Bacteria ferment carbohydrates into short-chain fatty acids (SCFA), convert dietary and endogenous nitrogenous compounds into ammonia and microbial protein, and synthesize B vitamins. Absorption of SCFA provides energy for the gut epithelial cells and plays an important role in the absorption of Na and water. Ammonia absorption aids in the conservation of nitrogen and water. A larger gut capacity and longer digesta retention time provide herbivores with additional SCFA for maintenance energy and foregut-fermenting and copoprophagic hindgut-fermenting species with access to microbially synthesized protein and B vitamins. Protozoa and fungi also contribute nutrients to the host. This review discusses the contributions of gut microorganisms common to all vertebrates, the numerous digestive strategies that allow herbivores to maximize these contributions, and the effects of low-fiber diets and discontinuous feeding schedules on these microbial digestive processes.

Patterns of seasonality and group membership characterize the gut microbiota in a longitudinal study of wild Verreaux's sifakas (Propithecus verreauxi)

“…Whereas in humans, SCFAs provide around 6%–10% of the daily energy supply (Stevens & Hume, 1998), in folivorous primates this proportion can be as high as 57% (Popovich et al., 1997). Thus, microbial fermentation might compensate for reduced energy intake during the dry season, similar to what has been observed in black howler monkeys, which display an increase of Ruminococcaceae during reduced energy intake (Amato et al., 2015).…”

Rumen microbial (meta)genomics and its application to ruminant production

“…In mammals, the diversification of modern herbivore lineages -the ancestors of our livestock -increased dramatically with the appearance of grasses ,25 million years ago (Hume and Warner, 1980). As a result, herbivore species predominate among the total number of extant mammals and are among the largest terrestrial species (Stevens and Hume, 1998). Within herbivores, ruminants have enlarged their gastrointestinal tracts and increased the retention time of forages to facilitate the fermentation of feeds by their symbiotic microbes.…”

“…Within herbivores, ruminants have enlarged their gastrointestinal tracts and increased the retention time of forages to facilitate the fermentation of feeds by their symbiotic microbes. Ruminants have evolved the most sophisticated system to harbour and take advantage of microbes in their forestomach (Stevens and Hume, 1998;Clauss et al, 2010), making them very adaptable to a large variety of diets. This is a characteristic that was certainly an important domestication trait (Diamond, 1997 and2002) and that can be attributed directly to microbes.…”

Defining the nature of human γδ T cells: a biographical sketch of the highly empathetic

“…For example, omnivorous rodents and primates may have less of a need to maintain peace with a diverse population of microbiota in comparison to cows, sheep, rabbits and chickens for which microbes play a more significant role in digestion and metabolism. [21][22][23][24] Therefore, the immune cell repertoire that recognize more variable 'non-self' as dangerous (i.e., the features that we depend on from the adaptive immune system) may be less advantageous when balancing the need to protect beneficial or non-threatening microbes that are needed for sustenance and/or to prevent chronic inflammation.…”