My lab is interested in understanding the principles that govern bacterial morphology, a readily observable facet of microbial cell biology. One of the major unsolved questions in microbiology is how bacteria generate specific shapes. Bacteria exhibit an amazing diversity of shapes and sizes that are precisely reproduced at every generation, indicating that morphology plays an important role in the life of these bacteria (Figure 1). Impressive progress has been made in the past few years in understanding the mechanism of cell shape determination in a few model bacterial systems, including the discovery that bacteria possess a cytoskeleton, but we are still very far having a comprehensive understanding of how bacterial morphologies are generated. My lab takes advantage of recent technical advances in microscopy, construction of fluorescent fusion proteins, and high throughput sequencing, to make strides in understanding how bacteria generate specific morphologies.

In most bacteria, the cell wall is comprised of peptidoglycan and is a major determinant of cell shape. In a majority of rod-shaped bacteria, including E. coli, cells elongate by the lateral insertion of newly synthesized peptidoglycan along their sidewalls. In contrast, some rod-shaped bacteria utilize precise targeting of peptidoglycan to specific polar locations to enable cell elongation. Indeed, we have previously shown that constrained polar growth is responsible for elongation in many species of Rhizobiales, including Agrobacterium tumefaciens (Figure 2). My lab uses A. tumefaciens, a well-studied plant pathogen and causative agent of crown gall disease, as a model to understand how bacteria constrain peptidoglycan synthesis to specific cellular localizations. Presently, we are focused on addressing two key questions:

1. What is the mechanism underlying polar growth of A. tumefaciens?

2. What are the ecological and evolutionary benefits imparted by polar growth?

Knowledge gained though these studies will then be applied to enhance our understanding of the precisely targeted growth in other Alphaproteobacteria, including those that display remarkable morphologies. Our goal is to better understand the role of zonal peptidoglycan synthesis in generating both relatively simple and dramatically complex bacterial shapes.