Gastrointestinal microorganisms exist in symbiotic associations with animals. Microorganisms in the gut assist in the digestion of feedstuffs, help protect the animal from infections, and some microbes even synthesize and provide essential nutrients to their animal host. Therefore, understanding the complex symbiotic relationships between gastrointestinal microbes and their animal hosts can lead to the development of practices to improve animal performance and promote animal health.
Digestive Strategies:
Animals are often classified according to their digestive physiology and gastrointestinal microorganisms can be examined according to gut location: foregut (before gastric stomach), midgut (small intestine) and hindgut (large intestine) (4, 5). Enzymes secreted in the mouth and stomach assist in the breakdown of foods consumed by animals. Microorganisms residing in other areas of the gastrointestinal tract can also help breakdown feedstuffs by a process called fermentation. Fermentation is the anaerobic breakdown of organic compounds.
Pre-gastric, cecal and colonic fermenters are descriptive terms used to indicate the location in the digestive tract where the majority of microbial activity occurs. Pre-gastric fermenters (before the gastric stomach), include ruminants such as cows, sheep and giraffes. When the majority of fermentative activity occurs in the cecum, animals can be described as cecal fermenters (guinea pigs, rabbits, chinchillas, rats, etc.). Colonic fermenters (gorillas, ponies, elephants, etc.) have the majority of fermentation occurring in the large intestine.
The Angert laboratory has investigated the microbial communities residing in the gastrointestinal tracts of surgeonfish, guinea pigs, cows and gorillas. Therefore, the following discussion will focus on those animals.
Surgeonfish:
There are ~80 species of fish in the surgeonfish family (Acanthuridae). Most surgeonfish are herbivores (eat algae primarily), and the herbivorous species tend to have long intestinal tracts when compared with carnivorous fish of the same body size (4, 5). The lengthy intestinal tract allows for a longer retention time of digesta and permits ample fermentation. Surgeonfish host Epulopiscium spp., members of the Low G+C gram-positive bacterial lineage. Scientists have observed surgeonfish behavior in the wild, and found that juvenile surgeonfish consume the feces of adult surgeonfish (1). This behavior may help the fish develop their intestinal microbial communities.
