Holistic Fitness: Microbiomes are Part of the Holobiont’s Fitness

Holobiont fitness includes interactions between the host and its symbionts, between the symbionts themselves, as well as between the holobiont and the environment. The interaction between the microbiome and the host generally leads to improved fitness. Protection against pathogens is one of the most general and important expressions of involvement of resident microbiota in the optimal functioning of the holobiont. Provision of essential nutrients is another general benefaction of microbiomes to their holobionts. In humans, the gut microbiome is a complex ecosystem that plays an essential role in the catabolism of dietary fibers, production of vitamins and amino acids, detoxification of harmful chemicals, regulation of angiogenesis and blood pressure, and development of the innate and antigen-specific immune systems. Although the mechanisms are not clear, gut bacteria in man and mice influence obesity, behavior and affect the brain. In many animals and plants, microbiota assists holobionts in adaptation to temperature and other environmental changes. The holobiont is an authentic, unique, biological entity encompassing within it mutual and inseparable interactions among the players within the holobiont, including cross-regulation of gene expression. The vast involvement of the microbiome with the fitness of the holobiont has been unraveled mainly in the last decade. Future research will reveal many more holobiont fitness factors contributed by microbiomes.