Genome-wide transcriptome analysis of the adaptive response of Enterococcus faecalis to copper exposure

In this work we investigated the adaptive response of E. faecalis to Cu and the role of CopY, a Cu-dependent repressor, in the regulation of Cu metabolism. In doing so, we examined the whole-genome transcriptional response of E. faecalis wild-type (WT) and a Delta copY strain exposed to non-toxic Cu excess. The results indicated that after Cu exposure, most of the genes that displayed a significant change in their expression levels in the WT strain (135 of the 145 up-regulated genes and 115 of the 142 down-regulated genes) were also differentially expressed in the E. faecalis Delta copY strain. This extensive overlap in the transcriptional response, suggested that additional transcription factors mediate the response of E. faecalis to Cu. As a first step to analyze this possibility, we selected among the up-regulated genes five genes encoding putative transcriptional regulators and determined their expression levels at different times after Cu exposure. The temporal expression of these regulators was different from that of copY, which reached its maximum at the earliest time measured. Nevertheless, transcription elongation factor GreA, and members of Rrf2, Cro/CI and SorC/DeoR transcription factor families were induced shortly after Cu exposure, suggesting that these proteins are able to complement the role of CopY in the regulatory network activated by Cu. To our knowledge, this is the first report on the global transcriptional response to Cu in a member of this taxonomic group.