Low temperature (23?°C) increases expression of biofilm-, cold-shock- and RpoS-dependent genes in Escherichia coli K-12

摘要

Temperature serves as a cue to regulate gene expression in Escherichia coli and other bacteria. Using DNA microarrays, we identified 297 genes whose expression is increased at 23?°C compared to 37?°C in E. coli K-12. Of these genes, 122 are RpoS-controlled, confirming genome-wide the model that low temperature serves as a primary cue to trigger the general stress response. Several genes expressed at 23?°C overlap with the cold-shock response, suggesting that strategies used to adapt to sudden shifts in temperature also mediate long-term growth at 23?°C. Another category of genes more highly expressed at 23?°C are associated with biofilm development, implicating temperature as an important cue influencing this developmental pathway. In a candidate set of genes tested, the biofilm genes (adrA, bolA, mlrA, nhaR, csgA, yceP/bssS) and cold-shock genes (otsA, yceP/bssS) were found to be RpoS- and DsrA-dependent for their transcription at 23?°C. In contrast, transcription of three genes (ycgZ, dps and ymgB) was either partially or fully independent of these regulators, signifying there is an alternative thermoregulatory mechanism(s) that increases gene expression at 23?°C. Increased expression at 23?°C compared to 37?°C is retained in various media tested for most of the genes, supporting the relative importance of this cue in adaptation to changing environments. Both the RpoS-dependent gene otsA and the RpoS-independent gene ymgB demonstrated increased expression levels within 1?h after a shift from 37 to 23?°C, indicating a rapid response to this environmental cue. Despite changes in gene expression for many RpoS-dependent genes, experiments assessing growth rate at 23?°C and viability at 4?°C did not demonstrate significant impairment in rpoS?:?:?Tn10 or dsrA?:?:?cat mutant strains in comparison to the wild-type strain. Biofilm formation was favoured at low temperature and is moderately impaired in both the rpoS?:?:?Tn10 and dsrA?:?:?cat mutants at 23?°C, suggesting genes controlled by these regulators play a role necessary for optimal biofilm formation at 23?°C. Taken together, our data demonstrate that a large number of genes are increased in expression at 23?°C to globally respond to this environmental change and that at least two thermoregulatory pathways are involved in co-ordinating this response – the RpoS/DsrA pathway and an alternative thermoregulatory pathway, independent of these regulators.