Virulence of Phospholipase C Mutants of Pseudomonas aeruginosa PAO1 against the Silkworm, Bombyx mori

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To estimate the contribution of phospholipase C (PLC) in the virulence of Pseudomonas aeruginosa against Bombyx mori, PlcB, PlcH, and PlcN mutants were created by the sacB-based counterselection method. Insertion of Ωaac cassette (selection marker, Gm^R) in plcB, plcH, and plcN was confirmed by Southern hybridization and the mutants were designated as PAO1plcB, PAO1plcH, and PAO1plcN, respectively. Inactivation of PLC genes did not cause growth deficient in vitro. The culture filtrates of PAO1, PAO1plcB, and PAO1plcN had hemolytic activity, but not PAO1plcH. When the PLC mutants were inoculated into the fourth instar of Bombyx mori larvae, all mutants maintained high virulence, indicating that at least inactivation of a single plc gene in P. aeruginosa did not affect the virulence against B. mori. It was different from the results obtained in another Lepidopteran host model, Galleria mellonella.