Cellular organization in Agrobacterium tumefaciens

Bacterial cell structures are macromolecular features found among all types bacteria. They often serve essential or specialized functions, and are important contributors to the widespread diversity and success of bacteria. I have focused my research on the formation and localization of two of these structures in the plant pathogen Agrobacterium tumefaciens: the type IV secretion system (T4SS) and the bacterial cell envelope. A. tumefaciens is an Alphaproteobacterium uniquely capable of genetically transforming plant host cells during its infection process. DNA and protein substrates are transferred into plant cells via the T4SS, which forms multiple complexes around the bacterial circumference. To understand the mechanisms driving T4SS positioning, I assessed their spatial distribution by quantitative analysis and modeling. My findings indicate that these secretion complexes localize in a non-random periodic pattern along the cell perimeter. These results, along with additional plant infection studies, suggest this spatial organization serves to promote efficient delivery of substrates into host cellsA potential mechanism behind this periodic arrangement is the unipolar cell growth recently described for A. tumefaciens. To better understand this unusual growth mechanism, I carefully scrutinized growing cells, nascent peptidoglycan, and peptidoglycan synthesis components by electron and fluorescence microscopy. My results indicate that the unipolar growth process is surprisingly dynamic, multi-dimensional, and involves both novel and familiar components. These findings thus represent a significant departure from the canonical growth mechanism of E. coli and other well-studied bacilli