Webb, Jeremy S., Lau, Mathew and Kjelleberg, Staffan
Bacteriophage and phenotypic variation in Pseudomonas aeruginosa biofilm development.
Journal of Bacteriology, 186, (23), . (doi:10.1128/JB.186.23.8066-8073.2004).
A current question in biofilm research is whether biofilm-specific genetic processes can lead to differentiation
in physiology and function among biofilm cells. In Pseudomonas aeruginosa, phenotypic variants which
exhibit a small-colony phenotype on agar media and a markedly accelerated pattern of biofilm development
compared to that of the parental strain are often isolated from biofilms. We grew P. aeruginosa biofilms in glass
flow cell reactors and observed that the emergence of small-colony variants (SCVs) in the effluent runoff from
the biofilms correlated with the emergence of plaque-forming Pf1-like filamentous phage (designated Pf4) from
the biofilm. Because several recent studies have shown that bacteriophage genes are among the most highly
upregulated groups of genes during biofilm development, we investigated whether Pf4 plays a role in SCV
formation during P. aeruginosa biofilm development. We carried out immunoelectron microscopy using anti-
Pf4 antibodies and observed that SCV cells, but not parental-type cells, exhibited high densities of Pf4
filaments on the cell surface and that these filaments were often tightly interwoven into complex latticeworks
surrounding the cells. Moreover, infection of P. aeruginosa planktonic cultures with Pf4 caused the emergence
of SCVs within the culture. These SCVs exhibited enhanced attachment, accelerated biofilm development, and
large regions of dead and lysed cells inside microcolonies in a manner identical to that of SCVs obtained from
biofilms. We concluded that Pf4 can mediate phenotypic variation in P. aeruginosa biofilms. We also performed
partial sequencing and analysis of the Pf4 replicative form and identified a number of open reading frames not
previously recognized in the genome of P. aeruginosa, including a putative postsegregational killing operon.
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