Optimal Production Level of Antibiotics in a Competitive Community

To be or not to be—should a microbe put up a fight or conserve resources for a better cause? In a competitive environment with limited nutrients, microbes thrive among each other deploying a few strategies. To maximize its share, it can either enhance its growth or suppress opponents’ growth. It is postulated that maximal competitive fitness is achieved when there is a balance in resource allocation between self-growth and killing. We developed a theoretical framework to evaluate the cost associated with producing the biomolecular weaponry, as well as the growth advantage from freed-up resources by competitors. We studied a specific case of an engineered community composed of Bacillus subtilis and recombinant Escherichia coli with vio genes from Janthinobacterium lividum. Compounds produced by vio genes are bacteriostatic against Gram-positive bacteria including B. subtilis. We performed simple monoculture experiments to parametrize functions describing cost and benefit stemming from vio expression. We then evaluated the theory at predicting E. coli growth in cocultures, at various vio expression levels and seeding sizes.