Abstract

The “division of labour” strategy is common among microbial communities, as dividing burdensome tasks between members of a community alleviates the strain placed on individual cells. Exploiting this phenomenon in heterogeneous microbial co-cultures for industrial synthesis of valuable compounds is limited by inefficiencies in nutrient exchange and conflicting growth requirements. Here, we demonstrate a synthetic gene circuit which enables cells of an isogenic Escherichia coli population to carry out “metabolic time-sharing” by shifting between alternate metabolic states via temporal changes in gene expression. Further, we review techniques for monitoring such dynamic processes at the single-cell level, and discuss their current applications in bacterial studies. To validate that our circuit may be used to induce cooperative behaviours in microbial populations, we adapted this circuit to engineer cells that oscillate between distinct amino acid auxotrophy phenotypes, driven by the periodic silencing of key biosynthetic genes. Culturing a clonal time-sharing population with unsynchronized oscillators permits reciprocal amino acid cross-feeding, ultimately ensuring population viability. Through comparative growth experiments, we found that the fitness of our time-sharing population was comparable to that of a heterogeneous co-culture composed of E. coli auxotrophs similarly capable of cross-feeding amino acids. Although future studies would be needed to confirm this, our preliminary results suggest that metabolic time-sharing may be a viable alternative to synthetic heterogeneous co-cultures. As it may enable an entire complex biosynthetic pathway to be engineered into a single host with reduced metabolic burden, the metabolic time-sharing strategy demonstrated here could potentially be implemented for microbial bioproduction, among other widespread applications.