Transcriptome of swarming Proteus mirabilis.

Swarming motility by the urinary tract pathogen Proteus mirabilis has been a long-studied but little understood phenomenon. On agar, a P. mirabilis colony grows outward in a bull's-eye pattern formed by consecutive waves of rapid swarming followed by consolidation into shorter cells. To examine differential gene expression in these growth phases, a microarray was constructed based on the completed genome sequence and annotation. RNA was extracted from broth-cultured, swarming, and consolidation-phase cells to assess transcription during each of these growth states. A total of 587 genes were differentially expressed in broth-cultured cells versus swarming cells, and 527 genes were differentially expressed in broth-cultured cells versus consolidation-phase cells (consolidate). Flagellar genes were highly upregulated in both swarming cells and consolidation-phase cells. Fimbriae were downregulated in swarming cells, while genes involved in cell division and anaerobic growth were upregulated in broth-cultured cells. Direct comparison of swarming cells to consolidation-phase cells found that 541 genes were upregulated in consolidate, but only nine genes were upregulated in swarm cells. Genes involved in flagellar biosynthesis, oligopeptide transport, amino acid import and metabolism, cell division, and phage were upregulated in consolidate. Mutation of dppA, oppB, and cysJ, upregulated during consolidation compared to during swarming, revealed that although these genes play a minor role in swarming, dppA and cysJ are required during ascending urinary tract infection. Swarming on agar to which chloramphenicol had been added suggested that protein synthesis is not required for swarming. These data suggest that the consolidation phase is a state in which P. mirabilis prepares for the next wave of swarming.