Cloning and characterisation of the rpoS gene from plant growth-promoting Pseudomonas putida WCS358: RpoS is not involved in siderophore and homoserine lactone production

The rpoS gene which encodes a stationary phase sigma factor has been identi fied and characterised from the rhizosphere-colonising plant growth-promoti ng Pseudomonas putida strain WCS358. The predicted protein sequence has ext ensive homologies with the RpoS proteins form other bacteria, in particular with the RpoS sigma factors of the fluorescent pseudomonads. A genomic tra nsposon insertion in the rpoS gene was constructed, these mutants were anal ysed for their ability to produce siderophore (iron-transport agent) and th e autoinducer quorum-sensing molecules called homoserine lactones (AHL). It was determined that RpoS was not involved in the regulation of siderophore and AHL production, synthesis of these molecules is important for gene exp ression at stationary phase. P. putida WCS358 produces at least three diffe rent AHL molecules. (C) 1999 Elsevier Science B.V. All rights reserved.