title: An alternative physiological role for the EmhABC efflux pump in Pseudomonas fluorescens cLP6a.
abstract: BACKGROUND
  Efflux pumps belonging to the resistance-nodulation-division (RND) superfamily in bacteria are involved in antibiotic resistance and solvent tolerance but have an unknown physiological role. EmhABC, a RND-type efflux pump in Pseudomonas fluorescens strain cLP6a, extrudes hydrophobic antibiotics, dyes and polycyclic aromatic hydrocarbons including phenanthrene. The effects of physico-chemical factors such as temperature or antibiotics on the activity and expression of EmhABC were determined in order to deduce its physiological role(s) in strain cLP6a in comparison to the emhB disruptant strain, cLP6a-1.
  
  
  RESULTS
  Efflux assays conducted with (14)C-phenanthrene showed that EmhABC activity is affected by incubation temperature. Increased phenanthrene efflux was measured in cLP6a cells grown at 10°C and decreased efflux was observed at 35°C compared with cells grown at the optimum temperature of 28°C. Membrane fatty acids in cLP6a cells were substantially altered by changes in growth temperature and in the presence of tetracycline. Changed membrane fatty acids and increased membrane permeability were associated with ~30-fold increased expression of emhABC in cLP6a cells grown at 35°C, and with increased extracellular free fatty acids. Growth of P. fluorescens cLP6a at supra-optimal temperature was enhanced by the presence of EmhABC compared to strain cLP6a-1.
  
  
  CONCLUSIONS
  Combined, these observations suggest that the EmhABC efflux pump may be involved in the management of membrane stress effects such as those due to unfavourable incubation temperatures. Efflux of fatty acids replaced as a result of membrane damage or phospholipid turnover may be the primary physiological role of the EmhABC efflux pump in P. fluorescens cLP6a.
authors.affiliation: Department of Biological Sciences, University of Alberta, Edmonton, Canada.
authors.forename: Abigail A
authors.initials: AA
authors.lastname: Adebusuyi
authors.forename: Julia M
authors.initials: JM
authors.lastname: Foght
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001426:Bacterial Proteins / Q000502:physiology*; D002463:Cell Membrane Permeability; D003470:Culture Media; D024901:Drug Resistance, Multiple, Bacterial; D005227:Fatty Acids / Q000032:analysis; D015964:Gene Expression Regulation, Bacterial; D026901:Membrane Transport Proteins / Q000502:physiology*; D010616:Phenanthrenes / Q000378:metabolism; D011551:Pseudomonas fluorescens / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D013696:Temperature
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D003470:Culture Media; D005227:Fatty Acids; D026901:Membrane Transport Proteins; D010616:Phenanthrenes; C031181:phenanthrene
references.citation: Antimicrob Agents Chemother. 2008 Dec;52(12):4478-82
references.pmid: 18838593
references.citation: J Bacteriol. 2006 Jan;188(1):115-23
references.pmid: 16352827
references.citation: Nat Rev Microbiol. 2006 Aug;4(8):629-36
references.pmid: 16845433
references.citation: Environ Microbiol. 2007 Jun;9(6):1550-61
references.pmid: 17504492
references.citation: FEMS Microbiol Lett. 2001 Jun 12;200(1):17-24
references.pmid: 11410343
references.citation: Microbiol Rev. 1995 Jun;59(2):201-22
references.pmid: 7603409
references.citation: Antimicrob Agents Chemother. 2005 May;49(5):1915-26
references.pmid: 15855514
references.citation: J Proteome Res. 2010 Jun 4;9(6):2957-67
references.pmid: 20373734
references.citation: J Bacteriol. 2009 Jul;191(13):4276-85
references.pmid: 19411325
references.citation: FEMS Microbiol Rev. 2010 Jul;34(4):554-87
references.pmid: 20337722
references.citation: Nat Protoc. 2008;3(2):163-75
references.pmid: 18274517
references.citation: Can J Biochem Physiol. 1959 Aug;37(8):911-7
references.pmid: 13671378
references.citation: Genome Biol. 2009;10(5):R51
references.pmid: 19432983
references.citation: Nat Rev Microbiol. 2008 Mar;6(3):222-33
references.pmid: 18264115
references.citation: Curr Opin Microbiol. 2009 Oct;12(5):512-9
references.pmid: 19664953
references.citation: Microbiology (Reading). 2004 Apr;150(Pt 4):853-864
references.pmid: 15073295
references.citation: Biochim Biophys Acta. 2009 May;1794(5):834-43
references.pmid: 19230852
references.citation: Appl Environ Microbiol. 2004 Feb;70(2):745-51
references.pmid: 14766550
references.citation: J Microbiol Methods. 2003 Feb;52(2):149-82
references.pmid: 12459238
references.citation: Nature. 2009 May 21;459(7245):379-85
references.pmid: 19458714
references.citation: Biochim Biophys Acta. 2009 May;1794(5):769-81
references.pmid: 19026770
references.citation: J Appl Microbiol. 2008 Jul;105(1):271-8
references.pmid: 18284486
references.citation: Biotechniques. 2005 Jul;39(1):75-85
references.pmid: 16060372
references.citation: J Bacteriol. 2005 Aug;187(15):5341-6
references.pmid: 16030228
references.citation: J Bacteriol. 2003 Nov;185(21):6233-40
references.pmid: 14563857
references.citation: J Appl Microbiol. 1998 Jan;84(1):90-6
references.pmid: 15244062
references.citation: Appl Environ Microbiol. 2000 Dec;66(12):5387-92
references.pmid: 11097918
references.citation: Biodegradation. 1996 Aug;7(4):353-66
references.pmid: 8987893
references.citation: Microbiology (Reading). 2001 Jan;147(Pt 1):43-51
references.pmid: 11160799
references.citation: J Exp Med. 2002 Jul 1;196(1):109-18
references.pmid: 12093875
references.citation: J Bacteriol. 2006 Mar;188(5):1847-55
references.pmid: 16484195