Grant: Operating Grant

Historically, bacteria have been viewed as simple organisms with little internal organization, often described as mere 'bags of enzymes'. More recently we have come to appreciate the often elaborate schemes bacteria adopt to organize their internal spaces, including filamentous cytoskeletons that move and position objects within the cell. Like more complex organisms, bacteria use cytoskeletal filaments to move DNA and ensure that both daughter cells get a copy when the cell divides. This process of DNA segregation is important not only for the bacterial genome, but also for plasmids - small pieces of DNA that can be spread among bacteria and often encode bacterial toxins and virulence factors. Without active segregation by the cytoskeleton many plasmids are lost from bacterial populations. Understanding how the machinery of plasmid segregation works at the detailed molecular level will provide opportunities to effectively disrupt the process in combating pathogenic bacteria. Here, we focus on segregation systems driven by bacterial actins, distant relatives of the cytoskeletal filament actin that plays roles in cell movement, cell division, intracellular organization, cell-cell interactions, and muscle contraction in higher organisms. Great progress has been made in recent years in characterizing bacterial actins both in vitro and in cells, revealing a surprising diversity of filament forms and dynamic behaviours. One of the central challenges now is to understand the detailed structures of the molecular machines that drive plasmid segregation. To achieve this, we propose work that integrates multiple structural approaches, allowing us to visualize in three dimensions single molecules, large molecular machines, and entire cells. This work will provide a framework for understanding both the diversity and the common features of plasmid segregation in these systems, as well as insight into more basic features of actin function.