title: Timing and localization of rhamnolipid synthesis gene expression in Pseudomonas aeruginosa biofilms.
abstract: Pseudomonas aeruginosa biofilms can develop mushroom-like structures with stalks and caps consisting of discrete subpopulations of cells. Self-produced rhamnolipid surfactants have been shown to be important in development of the mushroom-like structures. The quorum-sensing-controlled rhlAB operon is required for rhamnolipid synthesis. We have introduced an rhlA-gfp fusion into a neutral site in the P. aeruginosa genome to study rhlAB promoter activity in rhamnolipid-producing biofilms. Expression of the rhlA-gfp fusion in biofilms requires the quorum-sensing signal butanoyl-homoserine lactone, but other factors are also required for expression. Early in biofilm development rhlA-gfp expression is low, even in the presence of added butanoyl-homoserine lactone. Expression of the fusion becomes apparent after microcolonies with a depth of >20 mum have formed and, as shown by differential labeling with rfp or fluorescent dyes, rhlA-gfp is preferentially expressed in the stalks rather than the caps of mature mushrooms. The rhlA-gfp expression pattern is not greatly influenced by addition of butanoyl-homoserine lactone to the biofilm growth medium. We propose that rhamnolipid synthesis occurs in biofilms after stalks have formed but prior to capping in the mushroom-like structures. The differential expression of rhlAB may play a role in the development of normal biofilm architecture.
authors.affiliation: Department of Microbiology, 540 EMRB, Roy and Lucille Carver College of Medicine, University of Iowa, Iowa City, IA 52242, USA.
authors.forename: Yannick
authors.initials: Y
authors.lastname: Lequette
authors.forename: E P
authors.initials: EP
authors.lastname: Greenberg
mesh_terms: D015107:4-Butyrolactone / Q000031:analogs & derivatives* / Q000494:pharmacology; D018441:Biofilms; D006017:Glycolipids / Q000096:biosynthesis*; D009876:Operon; D010933:Plankton / Q000235:genetics; D011550:Pseudomonas aeruginosa / Q000235:genetics*; D013997:Time Factors; D014158:Transcription, Genetic
chemical_list: D006017:Glycolipids; C418382:rhamnolipid; C088386:homoserine lactone; D015107:4-Butyrolactone