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Instant insight: DNA hitchhikers
15 November 2007
Brian Jones and Julian Marchesi, of University College Cork in Ireland, take a closer look at the genetic swap shops in our midst
The macrobiota is the collection of bacteria in the gut and its collective genetic material is the metagenome
Over time, the gut microbiota has co-evolved with humans, resulting in a microbial community that performs many beneficial functions for the host. These include preventing our colonisation by pathogens, extracting nutrients from the food we eat, controlling cell division in the intestinal epithelium and developing our immune system. However, studies have also highlighted that gut microbiota contribute to diseases such as colorectal cancer and inflammatory bowel disease.
The microbial community's significance in human development and its impact on host health, means understanding the ecosystem's activities and capabilities should facilitate enhancements in human health and disease prevention, especially when coupled with data regarding the host genome. Unfortunately, analysing this activity is not easy. Of the plethora of bacterial species residing in our guts, we can grow relatively few in the laboratory. So, instead, we use powerful culture-independent approaches in which the individual genomes of the population are treated as one collective genome, broken into smaller pieces and transferred into bacteria that we can easily grow in the lab. This collective genome is referred to as the metagenome.
For most of our lives the composition of our microbiota is stable and so are the functions it performs. However, the composition can vary between individuals and so too could the relative outputs from these different communities. This difference makes the gut microbiota an important source of variation between individuals and potentially affects risk factors for numerous diseases. Ultimately, differences in our gut microbes may serve to increase the risk of certain diseases for some people while reducing it for others.
MGE can also pick up genes from a host bacterium and then carry these with them when they move. This promiscuity promotes gene flow within bacterial populations, and allows genes to move into an established population from bacteria that are just passing through. In the human gut, HGT could introduce new functions to the bacterial community and is likely to be important in its adaptability to changes in the gut environment.
So, if human and bacterial co-evolution has selected for a microbiota adapted to life in the gut, and in an intimate symbiotic relationship with the human host, the pool of genes in the microbiota has likely been shaped to reflect this. By looking at the gene pool - the mobile metagenome - we are likely to identify important functions of the gut microbiota. It may also lead to strategies for manipulating these functions and, considering the link between the microbiota and human health, could have important implications for disease treatment.
Read Jones and Marchesi's highlight 'Accessing the mobile metagenome of the human gut microbiota' in issue 11 of Molecular BioSystems.
Julian Marchesi's homepage
at University College Cork
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Link to journal article
Accessing the mobile metagenome of the human gut microbiota
Brian V. Jones and Julian R. Marchesi, Mol. BioSyst., 2007, 3, 749
Also of interest
Mammalian antimicrobial proteins and peptides: overview on the RNase A superfamily members involved in innate host defence
Ester Boix and M. Victòria Nogués, Mol. BioSyst., 2007, 3, 317