Engineering synthetic receptors in Bacillus subtilis

Abstract

Engineering signaling processes is central to building customized cells with bespoke novel functions. However, there are relatively few examples of engineering cellular control in response to artificial extracellular ligands, likely due to the complexity of engineering receptor sensor elements. Increasingly, there is also agreement that we may further our current understanding of endogenous signaling pathways through engineering new signaling behaviours. The lack of control over when and how bacterial endospores germinate has limited their use as a potential chassis for biotechnology purposes. Despite spore germination being best described in Bacillus subilis, there are still many fundamental questions about the mechanisms underlying germination. Yet, spores offer attractive characteristics over other candidates for use in biotechnology since they are inexpensive to prepare, are able to withstand harsh environmental conditions and can be stored at room temperature after dessication. Here, we describe a novel sensor system in spores of Bacillus subtilis that can detect small molecules, peptides and protein ligands. We exploit the modularity of a kinase germination receptor to engineer control over spore germination using synthetic receptors. Through engineering synthetic germination receptors we reveal unknown features of endogenous germination pathways in B. subtilis. This research contributes to our understanding of germination behaviour in B. subtilis spores and the complexity of which is necessary to understand in order for the potential of spore-based applications in biotechnology to be achieved. Using the same engineering strategy, we also describe how a synthetic receptor may regulate gene expression in cells of B. subtilis, which demonstrates the robustness of this approach.