The complexity of a microbiome is daunting. A human gut microbiome may have over 1,000 individual species of bacteria that co-exist stably over years or possibly over generations. We lack an understanding of the forces that contribute to this surprising stability. In this workshop, we will dive in and examine stripped down systems to test hypotheses on how the simplest microbiomes are defined and what mechanisms they use to remain stable. The example of the circadian clock − the biological timekeeping mechanism that sculpts our inner day − will be invoked to explore how a regular, systematic, daily stimulus shapes the composition of the gut microbiome of the mouse over the course of a day. | The keynote lecturer Javier A. Ceja-Navarro is Associate Professor for Biological Systems and Engineering at Lawrence Berkeley National Laboratory.