RpmA is required for nonopsonic phagocytosis of Pseudomonas aeruginosa

Pseudomonas aeruginosa causes severe respiratory tract infections in patien ts with cystic fibrosis (CF). We have been examining nonopsonic phagocytosi s of P. aeruginosa by macrophages. To study the P. aeruginosa-macrophage in teraction at the molecular level, we have constructed a transposon Tn5G ban k in a clinical isolate of P. aeruginosa (strain 4020) and identified mutan ts resistant to nonopsonic phagocytosis. Phagocytosis-resistant mutants mer e enriched by passaging the transposon bank over 18 macrophage monolayers. Of 900 individual mutants isolated from this enriched pool in a nonopsonic phagocytosis assay, we identified 85 putative mutants that were resistant t o phagocytosis. In this study, we have characterized one of these transposo n mutants, P. aeruginosa 4020 H27A, which was poorly ingested. H27A possess ed a Tn5G insertion in a gene encoding a protein with homology to the MotA proteins of several species of bacteria. We have called this gene rpmA for required for phagocytosis by macrophages. RpmA is one of two MotA paralogs in P. aeruginosa. This rpmA::Tn5G mutant was motile both on agar plates and in visual examination of wet mounts. The phagocytosis defect was partially complemented by providing the rpmA gene in trans and fully complemented wh en both rpmA and rpmB were provided. A rpmA null mutant was ingested by mac rophages similar to the H27A transposon mutant. These data suggest that the rpmA and rpmB gene products are required for the efficient ingestion of P. aeruginosa by macrophages.