REQUIREMENT FOR FLHA IN FLAGELLA ASSEMBLY AND SWARM-CELL DIFFERENTIATION BY PROTEUS-MIRABILIS

Swarming by Proteus mirabilis is characterized by cycles of rapid popu lation migration across surfaces, following differentiation of typical rods into long, aseptate swarm cells that overexpress flagella and vi rulence factors, particularly haemolysin, A non-swarming Tn5phoA mutan t was unable to synthesize flagella, to fully elongate or to induce hi gh levels of the toxin. The mutation lay within a 2091 bp gene encodin g a homologue of the Escherichia coli FlhA belonging to a family of pr oteins that are required for assembly of flagella or virulence protein s and that are suggested to act either directly in membrane translocat ion and/or in regulating synthesis of the export apparatus. In trans e xpression of multicopy flhA restored cell elongation and migration and generated differentiation-specific hyperexpression of flagellin and t oxin genes to levels above those seen in the wild-type strain. Transcr iption of flhA was strongly induced during differentiation, from its o wn putative sigma(28) promoter, The results suggest a mechanistic coup ling of flagella assembly and swarm-cell differentiation.