A novel regulatory module important for cell cycle regulation in the stalked budding bacterium Hyphomonas neptunium

Unlike many bacterial model organisms, the alphaproteobacterium Hyphomonas neptunium does not undergo binary fission but generates offspring through the formation of buds at the end of a stalk-like cellular extension. The control of this intricate biphasic life cycle requires a precise regulation of cell cycle progression, morphogenesis, and cell division. Here, we report the identification of a two-component signaling protein that is critical for normal growth and development in H. neptunium. A deletion mutant shows pleiotropic defects, including severely swollen mother cell bodies and growth defects. This new regulator is part of a regulatory module whose components mediate essential cellular functions and show cell cycle-dependent localization patterns. Together, our results reveal the existence of a novel and conserved, regulatory pathway that contributes to the regulation of cellular development in H. neptunium and, potentially, also other members of the alphaproteobacterial lineage.