Functions of the Microbiota
Essential Functions
Though the microbiota is a dynamic and constantly changing ecosystem, it has a number of functions essential for normal metabolic, immunologic, neurologic and structural health[1]. An optimal or balanced microbiota can perform these functions more efficiently, ultimately having beneficial effects on the hosts nutritional health and immunological resistance[2].
Fermentation of Indigestible Fibres
One of the major, well-known functions of the microbiota is the fermentation of indigestible fibres to produce short chain fatty acids (SCFA)[3]. Propionate, acetate and butyrate are key SCFA produced from this fermentative process and have many host benefits such as providing vital nutrition for intestinal epithelial cells, modulating immune function, and increasing mucosal blood flow[2][4][5]. Specifically, acetate is utilised for lipid metabolism, propionate for gluconeogenesis and butyrate is utilised as a key energy source for enterocytes and colonocytes[6][7].
Additionally, lactic acid is a by-product of the fermentation process. It plays a vital role in the intestinal ecosystem such as turnover of epithelial cells, acting as a food source for other SCFA producing bacteria[2] and producing an unfavourable local environment for pathogenic bacteria such as Salmonella spp. and E. coli by altering pH[8].
Vitamin Synthesis
The gut microbiota is responsible for synthesising certain vitamins, notably vitamin K and B group vitamins. Not only are these vitamins important for bacterial metabolism, but studies in germ-free rats have revealed the metabolic and physiological significance of some of these pathways in mammals.[9]
Gut Structural Development
The microbiota plays an important function in normal gut structural development which is supported by studies that have shown structural gut disorders associated with germ-free mice.[10] This is further reinforced by studies investigating the effect of faecal microbiota transplantation (FMT) in mice with intestinal disorders such as ulcerative colitis. These demonstrate FMT to have a therapeutic effect through remodelling of the intestinal flora and immune modulation.[11] Such research has led us to believe that the microbiota is vital in regulating the development of the intestinal barrier and its functions.[10]
Regulation of Pathogens
Research has revealed direct and indirect mechanisms by which the microbiota can regulate colonisation and eliminate pathogens, thus potentially limiting enteric infections. Commensal bacteria produce bacteriocins which specifically inhibit potentially pathogenic members of the same or similar bacterial species. Furthermore, commensals are able to alter the pH of the environment to prevent growth of certain pathogenic bacteria and prevent pathogenic infections.[12] Finally, the microbiota can indirectly prevent pathogenic colonisation by competing with pathogens for nutrients and promoting epithelial barrier function and integrity. The latter is achieved through mucus production and improving host immunity to defend against enteric infections.
Oral Tolerance
One of the more significant roles of the microbiota is in the development of oral tolerance. That is, the suppression of the immune responses to harmless orally ingested antigens and commensal bacteria. Specialised dendritic cells located in the intestinal mucosa are responsible for collecting intestinal antigens and critical for inducing tolerance through detection of luminal contents.[13] Rodent experimental models have demonstrated the ability of oral tolerance to prevent autoimmune and inflammatory diseases. With the abundance of dietary intolerance seen in veterinary practices, understanding how to provide an optimal environment for oral tolerance to develop is crucial for veterinarians.
Summary
Many of these functions can only be achieved through a healthy, balanced and diversified microbiota. Ultimately this can have a large impact on the overall health of the host through preventing infections, autoimmune and inflammatory diseases. Thus, understanding the functions of the microbiota is fundamentally important when choosing therapeutics, such as antibiotics and probiotics, as they can have significant long term effects on the host.
Author: Benjamin Sofaer BVSc, Veterinary Territory Manager at Protexin Veterinary. Protexin Veterinary is a brand of ADM Protexin Ltd
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References
- ↑ Adak A, Khan MR. An insight into gut microbiota and its functionalities, Cellular and Molecular Life Sciences 2018; 76(3):473-493
- ↑ 2.0 2.1 2.2 Ikeda-Ohtsubo W, Brugman S, Warden CH, Rebel JMJ, Folkerts G, Pieterse CMJ. How Can We Define “Optimal Microbiota?”: A Comparative Review of Structure and Functions of Microbiota of Animals, Fish, and Plants in Agriculture, Frontiers in Nutrition 2018; 5
- ↑ Krishnan S, Alden N, Lee K. Pathways and functions of gut microbiota metabolism impacting host physiology, Current Opinion in Biotechnology 2015; 36:137-145
- ↑ Savage DC. Gastrointestinal microflora in mammalian nutrition, Annual Review of Nutrition 1986; 6:155-178
- ↑ Marteau P, Seksik P, Lepage P, Doré J. Cellular and physiological effects of probiotics and prebiotics, Mini Reviews in Medicinal Chemistry 2004; 4(8):889-896
- ↑ Valdes AM, Walter J, Segal E, Spector TD. Role of the gut microbiota in nutrition and health, British Medical Journal 2018; 361:k2179
- ↑ Minamoto Y, Minamoto T, Isaiah A, Sattasathuchana P, Buono A, Rangachari VR, McNeely IH, Lidbury J, Steiner JM, Suchodolski JS. Fecal short‐chain fatty acid concentrations and dysbiosis in dogs with chronic enteropathy, Journal of Veterinary Internal Medicine 2019; 33(4):1608-1618
- ↑ Vieco-Saiz N, Belguesmia Y, Raspoet R, Auclair E, Gancel F, Kempf I, Drider D. Benefits and Inputs From Lactic Acid Bacteria and Their Bacteriocins as Alternatives to Antibiotic Growth Promoters During Food-Animal Production, Frontiers in Microbiology 2019; 10
- ↑ Rowland I, Gibson G, Heinken A, Scott K, Swann J, Thiele I, Tuohy K. Gut microbiota functions: metabolism of nutrients and other food components, European Journal of Nutrition 2017; 57(1):1-24
- ↑ 10.0 10.1 Di Mauro A, Neu J, Riezzo G, Raimondi F, Martinelli D, Francavilla R, Indrio F. Gastrointestinal function development and microbiota, Italian Journal of Pediatrics 2013; 39(1):15
- ↑ Zhou J, Zhou Z, Ji P, Ma M, Guo J, Jiang S. Effect of fecal microbiota transplantation on experimental colitis in mice, Experimental and Therapeutic Medicine 2019; 17(4):2581-2586
- ↑ Kamada N, Chen GY, Inohara N, Núñez G. Control of Pathogens and Pathobionts by the Gut Microbiota, Nature immunology 2013; 14(7):685-690
- ↑ Chistiakov DA, Bobryshev YV, Kozarov E, Sobenin IA, Orekhov AN. Intestinal mucosal tolerance and impact of gut microbiota to mucosal tolerance, Frontiers in Microbiology 2015; 5