The rsbA Locus and Swarming Behavior of Proteus Mirabilis

University Of Maryland Biotechnology Institute, Baltimore MD

Investigators

Abstract

Proteus mirabilis is a motile Gram-negative bacterium that was originally described and named by Hauser in 1885 for the character in Homer's Odyssey who "has the power of assuming different shapes in order to escape being questioned." What led Hauser to name this bacterium with such an imposing (and surprisingly astute) epithet? The answer: the phenomenon of swimmer-to-swarmer cell differentiation and swarming behavior. While differentiation of a P. mirabilis swimmer cell into a swarmer cell occurs at the level of the individual cell, swarming motility and behavior are characteristics associated with the coordinated movement of groups of swarmer cells, suggestive of a multicellular organism rather than a bacterial cell. Moreover, this behavior is cyclic in nature, so that the movement of the mass of bacteria is punctuated by periodic episodes during which the bacteria cease movement and dedifferentiate from swarmer cells back into swimmer cells. This dedifferentiation occurs while the bacteria are still exposed to the same stimulus that initially induced swarmer cell differentiation. The cyclic nature of P. mirabilis swarming behavior makes this phenomenon unique, even among the other bacterial species that produce swarming colonies. While other bacteria may swarm, none but P. mirabilis produce the clear and distinct cycles of differentiation and dedifferentiation that so well characterize this species. These cycles give rise to the bull's-eye colony pattern associated with P. mirabilis. Moreover, unlike the other swarming genera, phenotypically well characterized P. mirabilis mutants specifically defective in swarming behavior and pattern formation are available, thus providing the starting material for successful molecular analyses. The long-term goal of this research is to understand how bacteria communicate with one another during colony development and how that communication affects the expression of those genes required for differentiation and behavior. This research focuses specifically on the molecular mechanisms that control the onset of swarming migration and the bull's-eye pattern formation. The underlying hypothesis to be tested states that the development of swarming migration is a density-dependent process requiring both proteolysis from two extracellular proteases and the function of a histidine kinase sensor protein. The specific aim to be accomplished is:) Characterization of the inducer molecules (proteolytic products) responsible for density-dependent swarming migration. The results obtained from this study will answer the question "What role does AI-2 have in swarming migration behavior?"