title: Analysis of expression of the alpha-toxin gene (hla) of Staphylococcus aureus by using a chromosomally encoded hla::lacZ gene fusion.
abstract: The staphylococcal alpha-toxin (Hla) is a major virulence factor contributing to Staphylococcus aureus pathogenesis. To elucidate the conditions influencing hla expression, the determinant was fused to lacZ, the reporter gene coding for beta-galactosidase. The hla::lacZ fusion was integrated into the chromosome of the wild-type S. aureus strain Wood 46, leading to the variant Wood 46-3. Alpha-toxin expression was found to be dependent on temperature, showing a maximum at 42 degrees C. Furthermore, the indicator strain showed a growth phase-dependent hla regulation which was influenced by temperature. At 37 degrees C, induction of hla::lacZ expression occurred in the late exponential phase of growth, whereas at 42 degrees C, a strong induction was observed as early as the mid-exponential phase. These observations were verified by Northern blot analysis of hla mRNA and by Western blot (immunoblot) analysis of culture supernatants of strain Wood 46. It was additionally found that the induction of hla transcription at 42 degrees C was not coupled with higher concentrations of agr RNAIII, the effector molecule of the global regulator agr. Furthermore, expression of the alpha-toxin was repressed at a high osmolarity. It was also shown that oxygen is essential for hla expression and that cultivation of the S. aureus strain Wood 46-3 on solid medium and in the presence of carbon dioxide stimulated hla transcriptional activity.
authors.affiliation: Institut für Molekulare Infektionsbiologie der Universität Würzburg,Germany.
authors.forename: K
authors.initials: K
authors.lastname: Ohlsen
authors.forename: K P
authors.initials: KP
authors.lastname: Koller
authors.forename: J
authors.initials: J
authors.lastname: Hacker
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics; D001427:Bacterial Toxins / Q000235:genetics*; D002245:Carbon Dioxide / Q000378:metabolism; D003470:Culture Media; D015964:Gene Expression Regulation, Bacterial; D006460:Hemolysin Proteins / Q000235:genetics*; D010100:Oxygen / Q000378:metabolism; D012329:RNA, Bacterial / Q000235:genetics; D012333:RNA, Messenger / Q000235:genetics; D011993:Recombinant Fusion Proteins; D013211:Staphylococcus aureus / Q000235:genetics* / Q000254:growth & development / Q000472:pathogenicity; D013696:Temperature; D015534:Trans-Activators; D014157:Transcription Factors / Q000235:genetics; D014882:Water-Electrolyte Balance
chemical_list: C095698:Agr protein, Staphylococcus aureus; D001426:Bacterial Proteins; D001427:Bacterial Toxins; D003470:Culture Media; D006460:Hemolysin Proteins; D012329:RNA, Bacterial; D012333:RNA, Messenger; D011993:Recombinant Fusion Proteins; D015534:Trans-Activators; D014157:Transcription Factors; C021091:staphylococcal alpha-toxin; D002245:Carbon Dioxide; D010100:Oxygen