The intestinal microbiome is currently the subject of intensive research, as it is of great importance for human health. Intestinal bacteria play an essential role in the defense against dangerous pathogens, which is one of the reasons why the majority of them are among the good guys. On the other hand, some of our lodgers are more prevalent in specific diseases – for whatever reason. This also applies to the widespread but little-researched bacterium Segatella copri. The research group led by Prof Till Strowig at the Helmholtz Centre for Infection Research (HZI) wanted to determine what makes this bacterium tick. How does it adapt to its environment? And what signals does it react to?