Why was Escherichia coli thought to be a dominant member of the human gut microbial community in the past? What populations ARE important in the human gut and what evidence do we have that the specific bacteria present are important for human health?

Question

What will be an ideal response?

Answer 1

Answer: Escherichia coli was thought to be a dominant member of the human gut microbial community based on cultivation of microbes from the gut. Cultivation-dependent methods were biased towards those microbes that grow well under laboratory conditions and other members of the gut community were overlooked until new methods were developed for comparison. New methods based on 16S rRNA gene sequencing have revealed species-level diversity between individuals is extremely high, but at the phylum-level community composition patterns emerge. Important phyla in the human gut are Firmicutes, Bacteriodetes, Proteobacteria, and Actinobacteria. Evidence exists that there may be three different type of gut communities, or enterotypes, in the human population. These enterotypes seem to have different metabolic pathways that affect the processing of nutrients and the health of the gut. Gut microbes synthesize nutrients (e.g., amino acids and vitamins) that are important in the human diet. One example of a taxon affecting human health is the suggestion that the presence of Prevotella (a genus of Bacteriodetes) may contribute to obesity through increased production of volatile fatty acids that can be used as a source of energy (calories). Also, an increase in the number of methanogens in the gut may increase fermentation and the production of VFAs, thus increasing the number of calories available. (Other examples would be acceptable here as well.)