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Polar growth and cell division in Agrobacterium tumefaciens


Agrobacterium tumefaciens is a rod-shaped gram-negative bacterium, which elongates by unipolar addition of new cell envelope material. Approaching cell division, the growth pole transitions to a non-growing old pole, and the division site creates new growth poles in sibling cells. This thesis describes experiments concerning cell division and polar growth in A. tumefaciens. The cell division proteins FtsZ-GFP and FtsA-GFP localize to the growth pole in addition to the Z-ring at the mid-cell. The A. tumefaciens homolog of the Caulobacter crescentus polar organizing protein PopZCc (PopZAt) localizes specifically to growth poles. In contrast, the A. tumefaciens homolog of the C. crescentus polar organelle development protein PodJCc (PodJAt) 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, I created a deletion of podJAt . ΔpodJAt cells display ectopic growth poles (branching), growth poles that fail to transition to an old pole, and elongated cells that fail to divide. In ΔpodJAt cells, PopZAt -GFP persists at non-transitioning growth poles post division and also localizes to ectopic growth poles, as expected for a growth pole specific factor. Even though GFP-PodJAt does not localize to the midcell in wild type, deletion of podJAt impacts 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 PodJAt is a critical factor for polar growth, and ΔpodJAt displays a cell division phenotype. These results reveal intimate connections between polar growth and cell division in a model system displaying a novel form of cell growth.

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