Expression of csp genes in E. coli K-12 in defined rich and defined minimal media during normal growth, and after cold-shock

• qRT-PCR was used to quantify csp transcript levels in Escherichia coli K-12.
• Transcripts for some of the csp genes were present in the cell all the time (cspE).
• csp mRNA abundance changed with growth phase and cold-shock treatment.
• Only cspI was significantly induced by cold-shock in rich or minimal media.
• cspE was the most abundant csp transcript in the cells after cold-shock.

Cold-shock proteins (Csps) are a family of small nucleic acid-binding proteins found in 72% of sequenced bacterial genomes. Where it has been examined, at least one csp gene is required for cell viability. In Escherichia coli K-12, there are nine homologous csp genes named A–I. Regulation studies performed on individual members of this family have suggested that cspA, cspB, cspG, and cspI are cold-induced, cspC and cspE are constitutively expressed, cspD is stationary phase induced, and the induction patterns for cspF and cspH have yet to be determined. Aside from microarray studies, transcript levels from all nine csp genes have never been assayed using the same technique or in the same cells. The purpose of this study was to use quantitative RT-PCR to establish csp expression patterns for all nine csp genes at 37 °C in defined rich and defined minimal media, and after a shift to 15 °C for either 1 h or 4 h. We found that transcript levels for each of the csp genes changed throughout the growth curve. Transcripts for cspA, -B, and -E were more abundant than those detected for the other csp genes in defined rich medium. cspE mRNA levels in defined minimal medium were drastically higher than mRNA for the other csp genes. Of the nine csp genes, only cspI showed a significant increase in mRNA accumulation after cold-shock in defined rich medium. When mRNA accumulation was compared across the nine csp genes, there were more cspE transcripts in the cell than cspA, -B, -G, or -I transcripts after 1 h cold-shock in either defined rich or defined minimal media. In defined minimal medium, transcription of cspA, -B, -G, and -I was induced after cold-shock.