Loss of cspC function increases fitness in Escherichia coli K12

What is it about?

The CspA family of cold shock genes in Escherichia coli K-12 includes nine paralogs, cspA to cspI. Some of them have been implicated in cold stress adaptation. Screening for mutations among common laboratory E. coli strains showed a spectrum of variations including insertions of IS elements, deletion, and point mutation. These mutants showed loss of cspC expression in all but one case. Loss-of-function cspC mutants showed that they have a fitness advantage in broth culture over their isogenic wild-type derivatives. Conversely, introduction of mutated cspC alleles conferred a competitive fitness advantage to AB1157, a commonly used laboratory strain. This provides the evidence that loss of cspC expression is both necessary and sufficient to confer a gain of fitness as seen in broth culture over 24 h.

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Why is it important?

Though CspC is designated as a “cold shock protein,” it is not cold inducible. This work describes a novel role for CspC in cellular growth at 37°C and adds cspC to the small list of genes in E. coli whose loss-of-function alleles confer a selective advantage to the cells. We have demonstrated that loss of cspC expression confers a significant growth advantage to E. coli K-12 cells. Occurrence of cspC mutations in independent strains shows that they have a selective advantage. This selective advantage is manifested irrespective of the molecularmechanism that leads to loss of cspC function.