Multicopy suppression of a gacA mutation by the infC operon in Pseudomonasfluorescens CHA0: competition with the global translational regulator RsmA

The gacA gene of the biocontrol strain Pseudomonas fluorescens CHA0 codes f or a response regulator which, together with the sensor kinase GacS ( = Lem A), is required for the production of exoenzymes and secondary metabolites involved in biocontrol, including hydrogen cyanide (HCN). A gacA multicopy suppressor was isolated from a cosmid library of strain CHA0 and identified as the infC-rpml-rplT operon, which encodes the translation initiation fac tor IF3 and the ribosomal proteins L35 and L20. The efficiency of suppressi on was about 30%, as determined by the use of a GacA-controlled reporter co nstruct, i.e. a translational hcnA'-'lacZ fusion. Overexpression of the rsm A gene (coding for a global translational repressor) reversed the suppressi ve effect of the amplified infC operon. This finding suggests that some pro duct(s) of the infC operon can compete with RsmA at the level of translatio n in P. fluorescens CH40 and that important biocontrol traits can be regula ted at this level. (C) 2000 Federation of European Microbiological Societie s. Published by Elsevier Science B.V. All rights reserved.