Genetic Network Architecture and Environmental Cues Drive Spatial Organization of Phenotypic Division of Labor in Streptomyces coelicolor

Abstract

A number of bacteria are known to differentiate into cells with distinct phenotypic traits during processes such as biofilm formation or the development of reproductive structures. These cell types, by virtue of their specialized functions, embody a division of labor. However, how bacteria build spatial patterns of differentiated cells is not well understood. Here, we examine the factors that drive spatial patterns in divisions of labor in colonies of Streptomyces coelicolor, a multicellular bacterium capable of synthesizing an array of antibiotics and forming complex reproductive structures (e.g., aerial hyphae and spores). Using fluorescent reporters, we demonstrate that the pathways for antibiotic biosynthesis and aerial hypha formation are activated in distinct waves of gene expression that radiate outwards in S. coelicolor colonies. We also show that the spatiotemporal separation of these cell types depends on a key activator in the developmental pathway, AdpA. Importantly, when we manipulated local gradients by growing competing microbes nearby, or through physical disruption, expression in these pathways could be decoupled and/or disordered, respectively. Finally, the normal spatial organization of these cell types was partially restored with the addition of a siderophore, a public good made by these organisms, to the growth medium. Together, these results indicate that spatial divisions of labor in S. coelicolor colonies are determined by a combination of physiological gradients and regulatory network architecture, key factors that also drive patterns of cellular differentiation in multicellular eukaryotic organisms.IMPORTANCEStreptomyces coelicolor is a multicellular bacterium that differentiates into specialized cell types and produces a diverse array of natural products. While much is known about the genetic networks that regulate development and antibiotic biosynthesis in S. coelicolor, what drives the spatial organization of these activities within a colony remains to be explored. By using time-lapse microscopy to monitor gene expression in developmental and antibiotic biosynthesis pathways, we found that expression in these pathways occurs in spatiotemporally separated waves. Normally, expression of the antibiotic biosynthesis pathway preceded expression in the developmental pathway; however, this order was compromised in a mutant lacking a key developmental regulator. Furthermore, when we disrupted the local gradients during S. coelicolor growth, we observed disordered patterns of gene expression within colonies. Together, these results indicate that spatial divisions of labor in S. coelicolor colonies are determined by a combination of regulatory network architecture and physiological gradients.

Keywords: chemical gradients; development; division of labor; global regulatory networks; multicellular bacterium; natural products; regulatory networks; siderophores.