Targeted microarray analysis of stationary phase Escherichia coli O157:H7 subjected to disparate nutrient conditions.

AIMS

To determine how stress response and virulence gene expression of stationary phase (SP) Escherichia coli O157:H7 are affected by nutrient levels.

METHODS AND RESULTS

A targeted microarray (n=125 genes) was used to determine the impact of nutrient deprivation [15 min in 3-(N-Morpholino)propanesulfonic acid buffer] on SP E. coli O157:H7. In total, 24 genes were significantly affected (>1·5-fold; P <0·05) with 17 induced and seven attenuated. Additionally, 11 genes belonging to significantly affected stress response regulons were significantly induced (P<0·05), though <1·5-fold. Induced genes included global and specific stress response regulators, the mar operon, iron acquisition and virulence genes. In contrast, transcript for major porins and replicative genes were repressed. Comparison of the nutrient deprived transcriptome to that derived from nutrient replenished cells revealed a disparate transcriptome, with 44 genes expressed at significantly elevated levels in nutrient replenished cells, including all queried global and specific stress response regulators and key virulence genes. Genes expressed at elevated levels in nutrient deprived cells were related to σ(S) . The microarray data were validated by qRT-PCR.

CONCLUSIONS

SP E. coli O157:H7 were affected by nutrient deprivation, with both starvation-related and unrelated networks induced, thereby demonstrating how the E. coli O157:H7 stress response transcriptome is fine-tuned to environmental conditions. Further, by comparison of starved cells to cells provided with fresh nutrients, it is clear starved E. coli O157:H7 undergo massive physiological reprogramming dominated initially by stress response induction to adapt to a nutrient rich environment.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study demonstrated how σ(S) -induced SP E. coli O157:H7 remain highly sensitive and adaptable to environmental conditions. Further, by examining how starved cells respond to nutrient-rich conditions, we show preliminary adaptation to a nutrient rich environment is dominated by the induction of diverse stress response networks. Combined, this provides E. coli O157:H7 stress physiology-based knowledge that can be used to design more effective food safety interventions.