Host–Bacterial Symbiosis in Health and Disease

Abstract

All animals live in symbiosis. Shaped by eons of co-evolution, host-bacterial associations have developed into prosperous relationships creating mechanisms for mutual benefits to both microbe and host. No better example exists in biology than the astounding numbers of bacteria harbored by the lower gastrointestinal tract of mammals. The mammalian gut represents a complex ecosystem consisting of an extraordinary number of resident commensal bacteria existing in homeostasis with the host’s immune system. Most impressive about this relationship may be the concept that the host not only tolerates, but has evolved to require colonization by beneficial microorganisms, known as commensals, for various aspects of immune development and function. The microbiota provides critical signals that promote maturation of immune cells and tissues, leading to protection from infections by pathogens. Gut bacteria also appear to contribute to non-infectious immune disorders such as inflammatory bowel disease and autoimmunity. How the microbiota influences host immune responses is an active area of research with important implications for human health. This review synthesizes emerging findings and concepts that describe the mutualism between the microbiota and mammals, specifically emphasizing the role of gut bacteria in shaping an immune response that mediates the balance between health and disease. Unlocking how beneficial bacteria affect the development of the immune system may lead to novel and natural therapies based on harnessing the immunomodulatory properties of the microbiota.

The effect of microbial colonization on the host proteome varies by gastrointestinal location

“…Collectively, these bacteria constitute our microbiota, which outnumbers human cells in the body by a factor of 10 (Savage, 1977). The gut microbiota modulates various aspects of host physiology, including nutritional status, metabolism and immune-system maturation (Gill et al, 2006;Chow et al, 2010). Furthermore, the composition of the gut microbiota has been implicated in several human diseases, including type 1 diabetes (Wen et al, 2008), obesity Turnbaugh et al, 2006), asthma (Penders et al, 2007) and inflammatory bowel disease (Frank et al, 2007;Penders et al, 2007;Maslowski and Mackay, 2011).…”

Functional genome analysis of Bifidobacterium breve UCC2003 reveals type IVb tight adherence (Tad) pili as an essential and conserved host-colonization factor

“…GIT colonization by microbes is believed to play an essential part in metabolism and energy balance, in resisting pathogen colonization, in the maturation of the intestine, and in the education of the immune system (7)(8)(9)(10). The specific contribution of members of the Bifidobacterium genus to such activities is subject to much investigation and speculation (11), although it is widely accepted that their presence in the GIT may confer health benefits (12)(13)(14).…”

Functional genomics of Lactobacillus casei establishment in the gut

“…In parallel, some representative species, i.e., "model symbionts," now are being studied functionally (10). As it was done for pathogens, it is essential to develop the cellular microbiology of symbionts and particularly to identify the genes required for their establishment and persistence in the gut.…”