The role of hydrodynamics and AHL signalling molecules as determinants of the structure of pseudomonas aeruginosa biofilms

Abstract

The ability of two Pseudomonas aeruginosa PA01 wild type strains and two quorum sensing mutants to form biofilms in a recirculating continuous culture system was examined. Biofilms were grown under laminar and turbulent flow in parallel glass flow cells for between 9 and 12 d. One mutant, PANO67, is deficient in the production of BHL, however, it does produce OdDHL whereas a lasR lasI mutant does not produce OdDHL but is capable of producingBHL. The accumulation of biofilm biomass was estimated from the surface cover and the average microcolony thickness. The amount of biomass increased initially at a higher rate in the wild type strains than in the two quorum sensing mutants and a maximum was reached between 2 and 7 d after which there was some detachment of biofilm microcolonies. However, the biomass of the mutant strains steadily increased so that by the end of the experiments the mutant biofilms had a greater volume of biomass than the wild type strains. The results suggested no marked difference in the structure of the mutant biofilms compared to the wild type biofilms. However, the flow conditions had a profound influence on biofilm structure. Biofilms grown in turbulent flow consisted of filamentous streamers, while those grown in laminar flow consisted of a mono-layer of cells interspersed with circular microcolonies.

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