title: Increased transfer of a multidrug resistance plasmid in Escherichia coli biofilms at the air-liquid interface.
abstract: Although biofilms represent a common bacterial lifestyle in clinically and environmentally important habitats, there is scant information on the extent of gene transfer in these spatially structured populations. The objective of this study was to gain insight into factors that affect transfer of the promiscuous multidrug resistance plasmid pB10 in Escherichia coli biofilms. Biofilms were grown in different experimental settings, and plasmid transfer was monitored using laser scanning confocal microscopy and plate counting. In closed flow cells, plasmid transfer in surface-attached submerged biofilms was negligible. In contrast, a high plasmid transfer efficiency was observed in a biofilm floating at the air-liquid interface in an open flow cell with low flow rates. A vertical flow cell and a batch culture biofilm reactor were then used to detect plasmid transfer at different depths away from the air-liquid interface. Extensive plasmid transfer occurred only in a narrow zone near that interface. The much lower transfer frequencies in the lower zones coincided with rapidly decreasing oxygen concentrations. However, when an E. coli csrA mutant was used as the recipient, a thick biofilm was obtained at all depths, and plasmid transfer occurred at similar frequencies throughout. These results and data from separate aerobic and anaerobic matings suggest that oxygen can affect IncP-1 plasmid transfer efficiency, not only directly but also indirectly, through influencing population densities and therefore colocalization of donors and recipients. In conclusion, the air-liquid interface can be a hot spot for plasmid-mediated gene transfer due to high densities of juxtaposed donor and recipient cells.
authors.affiliation: Department of Biological Sciences, Initiative for Bioinformatics and Evolutionary Studies, University of Idaho, P.O. Box 443051, Moscow, ID 83844-3051, USA.
authors.forename: Jaroslaw E
authors.initials: JE
authors.lastname: Król
authors.forename: Hung Duc
authors.initials: HD
authors.lastname: Nguyen
authors.forename: Linda M
authors.initials: LM
authors.lastname: Rogers
authors.forename: Haluk
authors.initials: H
authors.lastname: Beyenal
authors.forename: Stephen M
authors.initials: SM
authors.lastname: Krone
authors.forename: Eva M
authors.initials: EM
authors.lastname: Top
mesh_terms: D018441:Biofilms; D002452:Cell Count; D003227:Conjugation, Genetic / Q000235:genetics; D003470:Culture Media; D024901:Drug Resistance, Multiple, Bacterial / Q000235:genetics*; D004926:Escherichia coli / Q000235:genetics* / Q000502:physiology; D022761:Gene Transfer, Horizontal / Q000235:genetics*; D018613:Microscopy, Confocal; D009154:Mutation; D010100:Oxygen / Q000378:metabolism; D010957:Plasmids / Q000235:genetics* / Q000378:metabolism*
chemical_list: D003470:Culture Media; D010100:Oxygen