ABSTRACTAgrobacterium tumefaciensis a rod-shaped Gram-negative bacterium that elongates by unipolar addition of new cell envelope material. Approaching cell division, the growth pole transitions to a nongrowing old pole, and the division site creates new growth poles in sibling cells. TheA. tumefacienshomolog of theCaulobacter crescentuspolar organizing protein PopZ localizes specifically to growth poles. In contrast, theA. tumefacienshomolog of theC. crescentuspolar organelle development protein PodJ localizes to the old pole early in the cell cycle and accumulates at the growth pole as the cell cycle proceeds. FtsA and FtsZ also localize to the growth pole for most of the cell cycle prior to Z-ring formation. To further characterize the function of polar localizing proteins, we created a deletion ofA. tumefacienspodJ(podJAt). ΔpodJAtcells display ectopic growth poles (branching), growth poles that fail to transition to an old pole, and elongated cells that fail to divide. In ΔpodJAtcells,A. tumefaciensPopZ-green fluorescent protein (PopZAt-GFP) persists at nontransitioning growth poles postdivision and also localizes to ectopic growth poles, as expected for a growth-pole-specific factor. Even though GFP-PodJAtdoes not localize to the midcell in the wild type, deletion ofpodJAtimpacts localization, stability, and function of Z-rings as assayed by localization of FtsA-GFP and FtsZ-GFP. Z-ring defects are further evidenced by minicell production. Together, these data indicate that PodJAtis a critical factor for polar growth and that ΔpodJAtcells display a cell division phenotype, likely because the growth pole cannot transition to an old pole.IMPORTANCEHow rod-shaped prokaryotes develop and maintain shape is complicated by the fact that at least two distinct species-specific growth modes exist: uniform sidewall insertion of cell envelope material, characterized in model organisms such asEscherichia coli, and unipolar growth, which occurs in several alphaproteobacteria, includingAgrobacterium tumefaciens. Essential components for unipolar growth are largely uncharacterized, and the mechanism constraining growth to one pole of a wild-type cell is unknown. Here, we report that the deletion of a polar development gene,podJAt, results in cells exhibiting ectopic polar growth, including multiple growth poles and aberrant localization of cell division and polar growth-associated proteins. These data suggest that PodJAtis a critical factor in normal polar growth and impacts cell division inA. tumefaciens.
Effect of ring topology in a stochastic model for Z-ring dynamics in bacteria
