In a recent article published in Nature Cell Biology, University of Chicago researchers identified two small molecules made by gut bacteria, queuine and its chemical precursor pre- queuosine 1 (preQ1), that compete to control our cells’ protein building machinery. The discovery reveals that these two bacterial metabolites act in opposite directions, particularly queuine to promote cell growth, and preQ1 to halt cell growth. The study suggests the growth-suppressing nature of specific microbial metabolites may be useful in developing new cancer therapies.