Garcia-Alcala, M.; Cluzel, P.

It is widely recognized from population-level measurements that increased production of unnecessary proteins leads to reduced bacterial growth rate, with this effect being particularly severe for flagellum synthesis. Here, we track the relationship between instantaneous growth rate variations and the activity of flagellar genes in lineages of single growing cells of E. coli. Surprisingly, we find that when flagellar gene expression is active, it is also coupled with increased growth rate. We determine that this phenomenon arises from growth bursts after divisions, which drive flagellar expression and temporarily alleviate the associated growth burden. Similar effects were observed with constitutive synthetic expression systems suggesting that an out-of-balance growth process may constitute a general strategy for mitigating the cost of expressing biosynthetically demanding genes in the single cell.