Species Specific Membrane Proteins of Legionellaceae

Abstract

The protein composition of the outer membrane and the whole cell wall of 21 strains representing 14 different serotypes of seven different Legionella species has been determined by sodium dodecylsulfate-polyacrylamide gel electrophoresis. The insoluble residue after extraction of cell envelopes with sodium laurylsarcosinate was considered to represent the outer membrane. Alternatively isopycnic sucrose density gradient centrifugation could be used; this approach gave similar results to the detergent method. Furthermore the effect of different methods of inactivation, e.g. treatment of the organisms with formaldehyde, heat or ether on the outer membrane proteins was investigated. Each of 14 strains from seven serogroups of Legionella pneumophila yielded identical patterns of outer membrane proteins. The most prominent feature is a L. pneumophila specific major outer-membrane protein with a molecular weight of 29,000 dalton. This characteristic component was present after every method of inactivation and could also be found as a prominent protein band in total membrane preparations of non-inactivated L. pneumophila. More protein bands were observed after heat or ether inactivation than after form-aldehyde inactivation. None of the other Legionella species under investigation contained the characteristic 29,000 dalton major outer membrane protein of Legionella pneumophila. Under all preparation conditions Legionella micdadei showed a characteristic intensively staining protein of 39,000 dalton. Neither the 29,000 dalton protein of L. pneumophila nor the 39,000 dalton component of L. micdadei were present in any of the other Legionella species. These other Legionella species exhibited on the contrary no single dominant membrane component but some weaker staining protein bands were observed and these were characteristic for each species. Both serogroups of Legionella longheachae yielded identical patterns. The analysis of membrane proteins of Legionellaceae presented here could prove as an alternative or a supporting technique for the identification of various Legionella species.