br GM composition and physiological functions in health The
GM composition and physiological functions in health The term microbiota refers to the living microbial community inhabit within a specific environment and encompasses bacteria, archaea, viruses (mainly phages), eukaryotes (mainly yeasts), even though bacteria outnumber the other domains. There is a symbiotic relationship between the human host and microorganisms that reside there, contributing to the maintenance of host health . GM is a complex ecosystem, not only by the diversity of species that inhabit the human GIT, but also by the way in which they interact with each other and the host . The entire human GIT is inhabited by approximately 100 trillion of bacteria and harbors the most diversified and colonized natural environment with >1000 different bacteria species, overcoming in ten times the number of human body 2-NBDG price [28,29]. This ecosystem consists of many native species that permanently colonize the GIT (autochthonous) and several other transient microorganisms (allochthonous species) . The mainly predominant bacterial phyla are Bacteroidetes (Gram-negative) and Firmicutes (Gram-positive), which together account over 90% of the total microbiota, while Actinobacteria (Gram-positive) and Proteobacteria (Gram-negative), Verrucomicrobia (Gram-negative), Fusobacteria (Gram-negative), and Cyanobacteria (Gram-negative) are present in lower abundance in the adult GIT [28,31]. In the last decade, the knowledge about GM diversity has been increased with the development of several culture-independent molecular techniques and approaches, in particular, with methods using regions of the 16S ribosomal RNA (16S rRNA) gene, a universally present microbial marker gene with highly conserved regions, which was used to establish prokaryotic phylogeny. Sequence analysis of the 16S rRNA gene was the first and one of the most used molecular tool applied to the identification of human microbiota . Recent advances in sequencing technology driven the metagenomics, allowing an important step GM knowledge, which has made a huge contribution to the understanding of human physiology and health. The Human Microbiome Project, by the NIH and the European Project – MetaHIT (Metagenomics of the Human Intestinal Tract), developed with the purpose of characterize dominant microbial communities from different parts of body, has generated useful reference genomes for many of the representative species [29,33,34]. Metagenomic shot-gun sequencing approaches of whole microbial communities, such as those found in the gut, have yielded near-complete gene catalogs that describe the abundance and diversity of genes that contribute to the maintenance and metabolism of the microbiota . In addition to metagenomics, functional approaches such as metatranscriptomics, metaproteomics and metabolomics also contribute for understanding the composition and abundance of gut microbiome and the subsequent impact on health and disease. These approaches have the potential to emphasize the complex crosstalk between humans and their microbial ecosystem as well as to emphasize the systemic influence of the latter beyond the intestine [35,36]. Despite all the technological advances, the high inter-individual variability on the GM composition makes difficult to define a core microbiome (all members of a microbial ecosystem) patterns that is shared by all humans. Recently, there has been a great interest in identifying the “healthy microbiota” profiling/signature and its variability in microbial populations in order to assess the deviations that are associated with disease states. This might open avenues to develop strategies to prevent and/or treat a broad spectrum of conditions associated with impaired GM composition and/or function, also referred as GM dysbiosis.
GM remodeling in healthy, in ageing and in diabetes
GM dysbiosis and progression of diabetic retinopathy