Article

Initiation of Biofilm Formation byPseudomonas aeruginosa 57RP Correlates with Emergence of Hyperpiliated and Highly Adherent Phenotypic Variants Deficient in Swimming, Swarming, and Twitching Motilities

INRS-Institut Armand-Frappier-Microbiologie et Biotechnologie, Laval, Québec, Canada H7V 1B7.
Journal of Bacteriology (Impact Factor: 2.69). 03/2001; 183(4):1195-204. DOI: 10.1128/JB.183.4.1195-1204.2001
Source: PubMed

ABSTRACT Pseudomonas aeruginosa is a ubiquitous environmental bacterium capable of forming biofilms on surfaces as a survival strategy. It exhibits a large variety of competition/virulence factors, such as three types of motilities: flagellum-mediated swimming, flagellum-mediated swarming, and type IV pilus-mediated twitching. A strategy frequently used by bacteria to survive changing environmental conditions is to create a phenotypically heterogeneous population by a mechanism called phase variation. In this report, we describe the characterization of phenotypic variants forming small, rough colonies that spontaneously emerged when P. aeruginosa 57RP was cultivated as a biofilm or in static liquid cultures. These small-colony (S) variants produced abundant type IV fimbriae, displayed defective swimming, swarming, and twitching motilities, and were impaired in chemotaxis. They also autoaggregated in liquid cultures and rapidly initiated the formation of strongly adherent biofilms. In contrast, the large-colony variant (parent form) was poorly adherent, homogeneously dispersed in liquid cultures, and produced scant polar fimbriae. Further analysis of the S variants demonstrated differences in a variety of other phenotypic traits, including increased production of pyocyanin and pyoverdine and reduced elastase activity. Under appropriate growth conditions, cells of each phenotype switched to the other phenotype at a fairly high frequency. We conclude that these S variants resulted from phase variation and were selectively enriched when P. aeruginosa 57RP was grown as a biofilm or in static liquid cultures. We propose that phase variation ensures the prior presence of phenotypic forms well adapted to initiate the formation of a biofilm as soon as environmental conditions are favorable.

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    • "The protocol described by Déziel et al. (2001) was followed for the motility evaluation. Bacteria were rinsed from an overnight culture, suspended in distilled and sterilized water and inoculated on King B (peptone 20 g/L, MgSO 4 7H 2 O 1.5 g/L, K 2 HPO 4 1.5 g/L, agar 15 g/L) culture medium containing 1.5, 0.5 and 0.3 % of agar for twitching, swarming and swimming tests, respectively, and incubated at 35 °C for 48 h. "
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    • "They are located at the pole of the cells and are involved in twitching motility, which is an unique type of movement across semi-solid surfaces. The movement results from the extension, tethering, and retraction of the pilus structure (O'Toole and Kolter 1998, Deziel at al. 2001, Skerker and Berg 2001). After surface colonization , the bacteria begin to communicate with one another in the process called " quorum sensing " and these signs guide the formation of microcolonies that will develop into mushroom-like pillars and give the mature biofilm an unique structure (Klausen et al. 2003, Kumar et al. 2009). "
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