For bacteria with complex life cycles involving several environmental niches, adaptability is key. The plant pathogen Agrobacterium tumefaciens is a master of adaptability as it lives two distinct lifestyles that each pose a unique set of challenges. In one, A. tumefaciens freely lives in the soil where it encounters many environmental stressors such as salinity, antibiotics, nutrient availability, changes in pH, and temperature that hinder its ability to grow. Upon encountering a potential host plant, A. tumefaciens transitions into a virulent, host-invading lifestyle state where it must adapt to survive a barrage of host defenses. This transformation and adaptability are driven by activation of the two component signaling pathway ChvGChvI. However, ChvG and ChvI are conserved in many bacteria that are not host-associated, suggesting that adaptation for host invasion is not the primary function of the pathway. I demonstrate activation of the pathway upon depletion of PBP1a, the primary driver of polar growth in A. tumefaciens, suggesting that ChvG-ChvI may be a more generalized stress pathway in response to defective polar growth. I expand on the role of ChvG-ChvI during host invasion and demonstrate its importance for growth during treatment with cell-wall targeting antibiotics and for growth in complex media. To better understand PBP1a contributions to polar growth, we sought to characterize the structure and function of PBP1a domains. We find that the enzymatic domains are necessary for PBP1a to function in elongation. In addition, we find that an OB-fold extension likely interacts with a negative regulator of PBP1a activity. To identify candidate regulators of PBP1a activity, we used PBP1a as a bait protein in an immunoprecipitation experiment and identified proteins that complex with PBP1a. These efforts have revealed several proteins involved in the synthesis and regulation of peptidoglycan metabolism and elongation. Overall, this work has improved our understanding of how polar growth is regulated in A. tumefaciens. 

Publications

Williams, M.A., Bouchier, J.M., Mason, A.K., Brown, P.J.B. Activation of ChvG-ChvI regulon by cell wall stress confers resistance to β-lactam antibiotics and initiates surface spreading in Agrobacterium tumefaciens (2022) PLoS Genetics, 18 (12), art. no. e1010274. DOI: 10.1371/journal.pgen.1010274

Williams, M.A., Aliashkevich, A., Krol, E., Kuru, E., Bouchier, J.M., Rittichier, J., Brun, Y.V., VanNieuwenhze, M.S., Becker, A., Cava, F., Brown, P.J.B. Unipolar Peptidoglycan Synthesis in the Rhizobiales Requires an Essential Class A Penicillin-Binding Protein (2021) mBio, 12 (5), art. no. e02346-21. DOI: 10.1128/mBio.02346-21

Committee Members

• Dr. Pamela J.B. Brown - Chair
• Dr. Ruthie Angelovici
• Dr. Elizabeth King
• Dr. Antje Heese