Biofilm formation by Pseudomonas fluorescens WCS365: a role for LapD

A role for the outer-membrane-associated LapA protein in early biofilm formation by Pseudomonas fluorescens WCS365 has previously been shown. This paper reports that lapD, a gene located adjacent to the lapA gene, also plays a role in biofilm formation. A mutation in lapD results in a conditional biofilm defect in a static assay - this biofilm phenotype is exacerbated when biofilm formation is assayed in a flow-cell system. Furthermore, a lapD mutation shows a partial defect in the transition from reversible to irreversible attachment, consistent with an early role for the lapD gene product in biofilm formation. LapD is shown to be localized to the inner membrane of P. fluorescens. The data show decreased LapA associated with the cell surface, but no apparent change in cytoplasmic levels of this protein or lapA transcription, in a lapD mutant. A model is proposed wherein the role of LapD in biofilm formation is modulating the secretion of the LapA adhesin.