(173d) Role of Positive Feedback Loops in Dictating Flagellar Gene Expression in Salmonella Typhimurium

Bacterial flagellum is a rotary motor that enables the cell to swim in liquid media and swarm on solid surfaces. In organisms such as Escherichia coli and Salmonella typhimurium, the flagellum is assembled in a sequential manner beginning at the base on the inner membrane and concluding with the filament. A critical feature of flagellar biogenesis is that gene expression is coupled to assembly, where protein secretion is the link. In these regards, flagellar assembly is a model system for organelle biogenesis and bacterial development.

In this talk, we will discuss the role of two interlocking positive feedback loops involved in regulating the flagellar assembly process. In particular, we have investigated the role of the FliZ and FliA-dependent feedback loops in regulating assembly. We hypothesized that these two loops fine-tune assembly dynamics and ensure that once a cell commits to building flagella it completes the process. To test this hypothesis, we measured gene expression dynamics in a number of mutants that altered the structure of these positive feedback loops at both population and single-cell resolution. Based on these results, we conclude that these positive feedback loops play an important role in governing the regulatory hierarchy involved in flagellar gene expression and, in conjunction with protein secretion, help the bacterium coordinate gene expression in response to the assembly state of the flagellum.