Selection of Attachment Mutants during the Continuous Culture of Pseudomonas fluorescens and Relationship between Attachment Ability and Surface Composition

Abstract

A strain of PseudomonasJIuorescens that had been isolated from a freshwater source on a plastic substratum was grown in continuous culture in minimal medium. The 'adsubble' process (adsorptive bubble separation process) was found to foam-fractionate wild-type cells from the fermenter during flow conditions. This selection pressure favoured the enrichment of two major classes of mutant, both having cell surface characteristics fundamentally different from the wild-type. The wild-type produced very little extracellular polysaccharide, whereas a 'mucoid' mutant, found predominantly in the aqueous-phase, produced an alginate exopolymer. The second class of mutant was isolated from the walls of the fermenter and, like the wild-type, produced little exopolymer. This mutant, with crenated colony morphology, showed increased attachment to solid surfaces compared to the wild-type and mucoid cells when assayed for attachment to polystyrene surfaces for 2 h. Outer-membrane protein, lipopolysaccharides and exopolysaccharides of the wild-type and both mutants were analysed. The results demonstrate the role of cell surface characteristics in the adaptability of the organism to micro-environments such as a solid/liquid or air/liquid interface or the aqueous phase.