Patrizia Brigidi, Department of Pharmacy and Biotechnology, University of Bologna, Italy

Human gut microbiome
The human gut harbors a complex and dynamic ecosystem of microbes, the gut microbiota (GM), that live in intimate relationship with the host, and have a large impact on several aspects of our physiology (1). This abundant microbial community includes members of all three domains of life: bacteria, which predominate, Eukarya and Archaea, up to1014 microbial cells. GM reaches the highest cell concentration in the colon, with a density of 1012 CFU/g of intestinal content, representing the most densely populated and biodiverse ecosystem on earth. It is composed of relatively few bacterial phyla, but it is notable for its species and strain level diversity, with thousands of species detected in the gut of the human population. This peculiar structure at lower phylogenetic levels varies dramatically from one individual to the next, with only a small phylogenetic overlap between people, and can change quickly over time in a single individual under environmental and endogenous pressures (2,3). Molded by the human genome, GM represents an adaptive component of the human superorganisms which provides functions indispensable to our life (4) and allows host adaptation at different timescales, optimizing host physiology from daily life to lifespan scales and human evolutionary history (5). Providing the host with functions important to regulate energetic homeostasis and immunological function, GM is strategic to keep metabolic and immunological homeostasis during the entire lifespan (6,7). Intestinal microbes produce indeed essential vitamins, and have the potential to metabolize a wide range of dietary substrates in a complex and intense microbiota-host transgenomic metabolism, deeply influencing our energy and metabolic homeostasis (8). According to an increasingly large body of evidence, GM may also have a major impact on our state of mind, through a bidirectional gut brain axis, governing anxiety and mood disorders (9). Different lifestyle and dietary factors, such as sanitization and antibiotic usage or high-fat diet, can force maladaptive changes in the microbiota configuration which could have negative effects on human health.

Bibliography

  • Mental health: thinking from the gut. Nature, 2015
  • Diversity, stability and resilience of the human gut microbiota. Nature, 2012
  • The long-term stability of the human gut microbiota. Science, 2013