Enhanced understanding of the microbiome is helping medicine

WHEN, at the turn of the century, the first human genomes were sequenced, many biologists felt they had had delivered into their hands the keys to unlocking numerous puzzles about disease. Since then there has indeed been a fruitful effort to understand how the thousands of human genes which control hormones, enzymes and other molecules of the body serve to regulate health. But, in an unexpected turn of events, it is also now apparent that the human genome is not the only one to which attention should be paid. Human guts contain microbes, lots of them. Added together, the genes in these bugs’ genomes amount to perhaps 150 times the number in the human genome alone. If the bacteria in question were doing little more than swimming around digesting lettuce, this would be of small consequence. But they are doing much more than that.

The members of the microbiome, as this community is known, are, to a surprising extent, partners of humanity. And when that partnership goes wrong, the results can be dreadful. Inflammatory bowel disease, autism, multiple sclerosis, obesity, diabetes and chronic-fatigue syndrome all seem to have links with dysbiosis, as an imbalance in the microbiome is known. Only this month, there was news that human gut microbes influence the way patients respond to a popular new type of cancer treatment called immunotherapy. Certain sorts of bacteria are abundant in patients who respond well. Antibiotics that kill these bacteria render immunotherapy less effective.