Staphylococcus aureus sigma B-dependent emergence of small-colony variants and biofilm production following exposure to Pseudomonas aeruginosa 4-hydroxy-2-heptylquinoline-N-oxide.
BACKGROUND
Staphylococcus aureus and Pseudomonas aeruginosa are often found together in the airways of cystic fibrosis (CF) patients. It was previously shown that the P. aeruginosa exoproduct 4-hydroxy-2-heptylquinoline-N-oxide (HQNO) suppresses the growth of S. aureus and provokes the emergence of small-colony variants (SCVs). The presence of S. aureus SCVs as well as biofilms have both been associated with chronic infections in CF.


RESULTS
We demonstrated that HQNO stimulates S. aureus to form a biofilm in association with the formation of SCVs. The emergence of SCVs and biofilm production under HQNO exposure was shown to be dependent on the activity of the stress- and colonization-related alternative sigma factor B (SigB). Analysis of gene expression revealed that exposure of a prototypical S. aureus strain to HQNO activates SigB, which was leading to an increase in the expression of the fibronectin-binding protein A and the biofilm-associated sarA genes. Conversely, the quorum sensing accessory gene regulator (agr) system and the alpha-hemolysin gene were repressed by HQNO. Experiments using culture supernatants from P. aeruginosa PAO1 and a double chamber co-culture model confirmed that P. aeruginosa stimulates biofilm formation and activates SigB in a S. aureus strain isolated from a CF patient. Furthermore, the supernatant from P. aeruginosa mutants unable to produce HQNO induced the production of biofilms by S. aureus to a lesser extent than the wild-type strain only in a S. aureus SigB-functional background.


CONCLUSIONS
These results suggest that S. aureus responds to HQNO from P. aeruginosa by forming SCVs and biofilms through SigB activation, a phenomenon that may contribute to the establishment of chronic infections in CF patients.
Mitchell
Gabriel
G
Centre d'Etude et de Valorisation de la Diversité Microbienne (CEVDM), Département de Biologie, Faculté des Sciences, Université de Sherbrooke, Sherbrooke, QC J1K2R1, Canada.
Séguin
David Lalonde
DL
Asselin
Ann-Elise
AE
Déziel
Eric
E
Cantin
André M
AM
Frost
Eric H
EH
Michaud
Sophie
S
Malouin
François
F
D001426:Bacterial Proteins / Q000378:metabolism*; D018441:Biofilms / Q000187:drug effects / Q000254:growth & development*; D015964:Gene Expression Regulation, Bacterial; D006912:Hydroxyquinolines / Q000494:pharmacology*; D008826:Microbial Sensitivity Tests; D018598:Minisatellite Repeats; D011550:Pseudomonas aeruginosa / Q000737:chemistry; D012329:RNA, Bacterial / Q000235:genetics; D012808:Sigma Factor / Q000378:metabolism*; D013211:Staphylococcus aureus / Q000187:drug effects* / Q000235:genetics / Q000254:growth & development / Q000378:metabolism
D001426:Bacterial Proteins; D006912:Hydroxyquinolines; D012329:RNA, Bacterial; C079011:SigB protein, Bacteria; D012808:Sigma Factor; C001333:2-(n-heptyl)-4-hydroxyquinoline N-oxide