A bioluminescence assay for screening thermoregulated genes in a psychrotrophic bacterium Pseudomonas fluorescens

Random transcription fusion delivery, with bacterial luciferase genes as re porter, was performed in the psychrotrophic bacterium Pseudomonas fluoresce ns. Direct screening on plates of the insertions allowed the isolation of f usions into thermoregulated genes with good accuracy, either in a library o f insertion fusions, or after genetic transfer of a putative regulatory mut ation. Using this method, it was shown that in Ps. fluorescens, nearly 40% of the genes are thermoregulated and belong to at least three classes accor ding to the maximal temperature of expression of the fused genes. This is m ore than had been estimated by a previous method, and demonstrates the impo rtance of thermoregulation in psychrotrophic bacteria. As this reporter is the first to be used for direct screening for genes regulated by temperatur e, it should be of great value in the study of mechanisms involved in adapt ation to this environmental factor.