Distinct dynamics and proximity networks of hub proteins at the prey-invading cell pole in a predatory bacterium

Abstract

In bacteria, cell poles function as subcellular compartments where proteins localize during specific lifecycle stages, orchestrated by polar "hub" proteins. Whereas most described bacteria inherit an "old" pole from the mother cell and a "new" pole from cell division, polarizing cells at birth, non-binary division poses challenges for establishing cell polarity, particularly for daughter cells inheriting only new poles. We investigated polarity dynamics in the obligate predatory bacterium Bdellovibrio bacteriovorus, proliferating through filamentous growth followed by non-binary division within prey bacteria. Monitoring the subcellular localization of two proteins known as polar hubs in other species, RomR and DivIVA, revealed RomR as an early polarity marker in B. bacteriovorus. RomR already marks the future anterior poles of the progeny during the predators growth phase, in a define time window closely following the onset of divisome assembly and the end of chromosome segregation. In contrast to RomRs stable unipolar localization in the progeny, DivIVA exhibits a dynamic pole-to-pole localization. This behaviour changes shortly before division of the elongated predator cell, where DivIVA accumulates at all septa and both poles. In vivo protein interaction networks for DivIVA and RomR, mapped through endogenous miniTurbo-based proximity labeling, further underscore their distinct roles in cell polarization and the importance of the anterior "invasive" cell pole in prey-predator interactions. Our work emphasizes the strict spatiotemporal coordination of cellular processes underlying B. bacteriovorus proliferation, offering insights into the subcellular organization of bacteria with filamentous growth and non-binary division.