Pyocin S2 (Sa) kills Pseudomonas aeruginosa strains via the FpvA type I ferripyoverdine receptor

Laboratory of Microbial Interactions, Department of Molecular and Cellular Interactions, VIB, Vrije Universiteit Brussel, Pleinlaan 2, 1050 Brussels, Belgium

^* To whom correspondence should be addressed. Email: pcornel{at}vub.ac.be.

	Abstract

Soluble pyocins (S-type) are Pseudomonas aeruginosa bacteriocins that kill non-immune P. aeruginosa strains via a specific receptor. The genes coding for pyocin Sa (killing protein and immunity protein) were cloned and expressed in E. coli. Sequence analysis revealed that Sa is identical to pyocin S2. Seventy-nine strains of P. aeruginosa were tested for their sensitivity to pyocins S1, S2 and S3 and their ferripyoverdine receptor typed by multiplex PCR. No strain was found to be sensitive to both S2 and S3, suggesting that the receptors for these two pyocins cannot co-exist in one strain. As expected, all S3-sensitive strains had the type II ferripyoverdine receptor gene fpvAII, confirming our previous reports. S1 killed strains irrespective of the type of ferripyoverdine receptor they produce. All S2-sensitive strains had the type I fpvA gene and inactivation of fpvAI in a S2-sensitive strain conferred resistance to the pyocin. Accordingly, complementation with fpvAI in trans restored sensitivity to S2. Some S2-resistant/fpvAI-positive strains where detected, the majority of which, except five, had the S1/S2 immunity gene. Comparison of fpvAI sequences from immunity-negative S2-sensitive and S2-resistant strains only revealed a valine to isoleucine substitution at position 46 of FpvAI. However, both fpvAI genes conferred both type I pyoverdine utilization and sensitivity to S2. When these two fpvAI genes were introduced in strain 7NSK2 mutated for fpvAII (type II pyoverdine receptor) and fpvB (alternative type I receptor), growth was observed in the presence of type I pyoverdine, and the strain became sensitive to S2. It was also found that type I pyoverdine could signal type II pyoverdine production via the FpvAI receptor in 7NSK2.