EFFECTS OF TEMPERATURE ON GROWTH AND SIDEROPHORE PRODUCTION OF PSEUDOMONAS-FLUORESCENS-PUTIDA STRAINS

Experiments performed at 25-degrees-C and 35-degrees-C on growth in vitro of fifty strains of the Pseudomonas fluorescens-putida cluster originating from temperate and tropical countries, allowed the establishment of an ecological classing according to the relative thermophilic nature of the strains. All the strains which grew normally at 35-degrees-C were from tropical origin. Indeed at this temperature, most of the strains from temperate countries grew slowly or not at all and they did not produce any fluorescent siderophores with a few exceptions, while tropical strains produced siderophores. Moreover it was observed that exopolysaccharide (EPS) synthesis is wholly inhibited at 35-degrees-C for all the strains (temperate and tropical strains as well). When the bacterial strains are subjected to a temperature of 41-degrees-C for 48 hours, resistance to this thermal stress is generally correlated to the tropical origin of the strain. Finally the colonizing behaviour of the Pseudomonas fluorescens-putida strains in relation to rhizosphere and tomato root systems differs on a characteristic way in terms of temperature. Assessing tomato roots colonizing capacity of a temperate (L26-1) and a tropical (M3-1) strains, it was observed that the tropical strain had a better colonizing capacity at 21-degrees-C and 33-degrees-C as well. Consequences of this thermosensitivity on establishment, survival and development of PGPR populations in substrates and in soils are discussed.