BioProject

This study was conducted to determine the impact of extreme temperatures, aiming at controlling microorganisms by cooking, on the physiology and the transcriptome of Escherichia coli. ABSTRACT: Because the genome of Escherichia coli K12 is well understood, this organism was used as a model to investigate physiological and molecular changes during cell adaptation and survival to cooking temperatures used in the food industry. Bacteria grown at 37°C to stationary phase in Brain Heart Infusion (BHI) broth, were heated at 58°C or 60°C to reach a process lethality value (F) of 2 and 3, or until an internal core temperature of 71°C was reached (control cooking temperature). Both growth recovery and cell membrane integrity were evaluated immediately after heating and a global transcription analysis was performed by using gene expression microarrays. Only cells heated at 58°C F = 2 were still able to grow on liquid or solid BHI after heat treatment. However, their transcriptome did not differ significantly compared to those of bacteria heated at 58°C F = 3 (P-FDR > 0.01) where no growth recovery was observed post treatment. Genome-wide transcriptomic data obtained at 71°C were distinct from the other treatments. Quantification of heat-shock genes expression by real-time PCR revealed that dnaK and groEL mRNA levels were significantly lower at 71°C than at 58°C and 60°C (P < 0.0001). Furthermore, despite of similar cell inactivation but growth on BHI media after heating, 132 and 8 genes were differentially expressed at 71°C when compared to 58°C and 60°C at F = 3 respectively (P-FDR < 0.01). Among them, genes like aroA, citE, glyS, oppB and asd, whose expression was up-regulated at 71°C, may be considered as good biomarkers to determine more accurately the efficiency of heat treatments. Overall design: Bacteria were submitted to four different heat-treatments. Biological replicates: 5 Controls grown to an optimal temperature of 37°C (and used to prepare a common reference for each array hybridization), 5 Treatment 1 (58°C F = 2), 4 Treatment 2 (58°C F = 3), 4 Treatment 3 (60°C F = 3), 5 Treatment 4 (core temperature of 71°C). Treatment replicates were randomly hybridized on 3 microarray slides Agilent 8x15K (total of 24 array areas). Equal amounts of the labeled control cDNA pool and labeled cDNA from one of the heated groups were mixed and hybridized on each array.