Enhanced Population Control in Synthetic Bacterial Consortium by Interconnected Carbon Cross-Feeding

Abstract

Engineered microbial consortia can provide several advantages over monocultures in terms of utilization of mixed substrates, resistance to perturbations, and division of labor in complex tasks. However, maintaining stability, reproducibility, and control over population levels in variable conditions can be challenging in multi-species cultures. In our study, we modeled and constructed a synthetic symbiotic consortium with a genetically encoded carbon cross-feeding system. The system is based on strains of Escherichia coli and Acinetobacter baylyi ADP1, both engineered to be incapable of growing on glucose on their own. In a culture supplemented with glucose as the sole carbon source, growth of the two strains is afforded by the exchange of gluconate and acetate, resulting in inherent control over carbon availability and population balance. We investigated the system robustness in terms of stability and population control under different inoculum ratios, substrate concentrations, and cultivation scales, both experimentally and by modeling. To illustrate how the system might facilitate division of genetic circuits among synthetic microbial consortia, a green fluorescent protein sensitive to pH and a slowly-maturing red fluorescent protein were expressed in the consortium as measures of a circuit's susceptibility to external and internal variability, respectively. The symbiotic consortium maintained stable and linear growth and circuit performance regardless of the initial substrate concentration or inoculum ratios. The de-veloped cross-feeding system provides simple and reliable means for population control without expression of non-native elements or external inducer addition, being potentially exploitable in consortia applications involving precisely defined cell tasks or division of labor.

Drawing up a collaborative contract: Amino acid cross‐feeding between interspecies bacterial pairs

“…The implication of natural costless secretion suggests new strategies for cross‐feeding in communities for biotechnology as cross‐fed metabolites that push flux towards your product of interest could be selected. Auxotrophy can also be used to fine‐tune community composition (Losoi et al, 2019; Ziesack et al, 2019), by engineering levels of metabolite secretion for auxotrophic pairs that fail to cross‐feed spontaneously we can maintain that organism at a lower cell density within the community. We can also selectively supplement media to increase or decrease the cell density of an auxotroph, allowing for control of community composition.…”