Gut microbes play wide-ranging roles in health and disease, but there has been a lack of tools to probe the relationship between microbial activity and host physiology. Two independent studies in mice published April 20 in the journal Cell have overcome this hurdle, making it possible to simultaneously visualize multiple bacterial strains in the gut by making them express unique combinations of fluorescent proteins. This approach allowed the researchers to pinpoint the location of the bacteria in the gut based on the rainbow of colors they emitted. Additionally, these tools also allowed precise control of the activity of bacterial genes in real time and in specific locations.