Induction of proteinases in Legionella by growth on agar containing serum

Non-proliferating cells of Legionella show a rather small proteolytic action on human serum proteins. However, if the strains grow on agar plates containing serum the proteolysis is very strong. This effect may be due to an induction of the appropriate enzymes by their substrates. The alterations of 24 investigated proteins demonstrated by immunoelectrophoresis show anodic shifts of bands and their disappearance (Table 1, Fig. 1-15). The shifted proteins are not degraded significantly. Their altered electrophoretic mobility may be due to a change of electrical charge by loss of one or a few end standing amino acids. The disappearance of bands in the immunoelectrophoretic assay and the simultaneous diminution of the protein concentration measured by the method of immunodiffusion suggests a proteolysis (Table 2). No inhibitory effect of the proteinase inhibitor aprotinin could be observed. The results suggest that the extent of the enzyme induction may be decisive for the virulence of a strain.