The autotransporter esterase EstA of Pseudomonas aeruginosa is required for rhamnolipid production, cell motility and biofilm formation

Institute For Molecular Enzyme Technology, Heinrich-Heine-University Duesseldorf, Research Centre Juelich, D-52426 Juelich, Germany; Biofilm Centre, University Duisburg-Essen, Geibelstr. 41 D-47057 Duisburg, Germany

^* To whom correspondence should be addressed. Email: f.rosenau{at}fz-juelich.de.

	Abstract

Pseudomonas aeruginosa PAO1 produces the biodetergent rhamnolipid and secretes it into the extracellular environment. The role of rhamnolipids in life cycle and pathogenicity of P. aeruginosa has not been completely understood, but they are known to affect outer membrane composition, cell motility and biofilm formation. This report is focussed on the influence of the outer membrane bound esterase EstA of P. aeruginosa PAO1 on rhamnolipid production. EstA is an autotransporter protein which exposes its catalytically active esterase domain on the cell surface. Here we report that the overexpression of EstA in the wildtype background of P. aeruginosa PAO1 results in an increased production of rhamnolipids whereas an estA deletion mutant produced only marginal amounts of rhamnolipids. Also the known rhamnolipid dependent cellular motility and biofilm formation were affected. Although only a dependence of swarming motility on rhamnolipids was known so far also the other kinds of motility displayed by P. aeruginosa PAO1 as swimming and twitching were affected by an estA mutation. In order to demonstrate that EstA enzyme activity is responsible for these effects, an inactive variant EstA* was constructed by replacement of the active serine by alanine. None of the mutant phenotypes could be complementd by expression of EstA*, demonstrating that the phenotypes affected by the estA mutation depend on the enzymatically active protein.