Temperature-dependent regulation of the lpxT gene in Escherichia coli and Pseudomonas aeruginosa

The LpxT protein modifies the outer membrane of Gram negative bacteria by phosphorylating the lipid A moiety of the lipopolysaccharide. Recently, we found that the expression of the lpxT gene of Pseudomonas aeruginosa (Pa) is post-transcriptionally regulated by an RNA thermometer (RNAT). An RNAT is a thermo-labile secondary structure that entraps the mRNA Translation Initiation Region (TIR) at low temperature, thus inhibiting ribosome binding. To assess whether also the Escherichia coli lpxT was regulated by temperature through a similar strategy, we assayed the expression of different lpxT-GFP translational fusions in the BW25113 strain at 28° and 42°C. Moreover, we analysed in the same strains and conditions the transcription profile of the chromosomal lpxT locus. We found that i) the lpxT transcript starts 29 nt upstream of the ORF start codon. Transcription from the promoter lpxTp is modulated both by temperature and growth phase; ii) the presence of the short lpxT 5’-UTR, which can form a stem-loop (SLlpxT), confers thermo-dependent expression to a downstream reporter gene; iii) mutations affecting SLlpxT stability impact on the reporter gene expression. On the whole our results suggest that transcriptional and post-transcriptional mechanisms cooperate in the complex regulation of Ec lpxT expression.