Through their effects on metabolism and immunity, bacteria in the gut affect whether medications will be effective for a given patient.

Animal studies and a few small clinical trials show it’s possible to get commensal microbes to protect against bone loss, rather than contribute to it.

Swirls of bacteria form on an agar plate.

Research in mice and humans is beginning to establish a link between the composition of microbes in the gut and immune responses to tumor cells, but the mechanisms are not yet clear.

As evidence grows that gut bacteria play roles in the development and persistence of food allergies, researchers begin to explore microbe-based interventions.

The microbiomes of men who have sex with men are associated with greater immune system activation and promote elevated rates of viral infection in vitro.

The gut microbiome has been linked to depression, schizophrenia, and other neurological conditions, but it’s not yet clear whether the relationship is causal.

A study fails to detect ancient proteins among the microbes, adding to the debate about whether peptides can survive tens of millions of years underground.

Independent scientists say the original analysis is flawed; the authors stand by their work and are seeking outside statisticians to reanalyze the data.