The dissertation discusses the proteins from the aegerolysin family, specifically the RahU protein of the opportunistic pathogen bacteria, Pseudomonas aeruginosa. The biology of P. aeruginosa, which exploits its host’s weak immune system to cause numerous infections, is described. The main focus of the dissertation was the preparation of the deletion mutants. The rahU gene was deleted from the P. aeruginosa genome by replacing it with the kanymicin cassette. The gene replacement was carried out by using the Lambda Red recombinase system. The purpose of this molecular tool was to gain the rahU deletion mutants, which enable us to obtain new insights into the biology of the RahU protein.