Histidine utilisation operon (hut) is upregulated at low temperature in the antarctic psychrotrophic bacterium Pseudomonas syringae

Abstract

The antarctic psychrotrophic bacterium Pseudomonas syringae was mutagenised using a transposon Tn5-OT182 which facilitates identification of promoter fusions expressing the reporter gene (lacZ) for β-galactosidase. Most mutants expressed β-galactosidase both at optimal growth temperature (20-22°C) and at low temperature (4°C). But a small percentage of the mutants (~5%) were unique in that they expressed β-galactosidase activity predominantly at low temperature. One such mutant was found to have an insertion in the gene for urocanase (hutU) of the histidine utilisation (hut) operon. Direct assay of urocanase and histidase activity in wild-type cells of various antarctic psychrotrophic strains including P. syringae, P. fluorescens and P. putida also suggested that the hut operon is expressed at an elevated level at low temperature.