Remodeling of the Streptococcus agalactiae transcriptome in response to growth temperature. Streptococcus agalactiae

To understand the extent to which GBS modify gene expression in response to temperatures encountered in the various hosts, we conducted a whole genome transcriptome analysis of organisms grown at 30°C and 40°C. We identified extensive transcriptome remodeling at various stages of growth, especially in the stationary phase (significant transcript changes occurred for 25% of the genes). A large proportion of genes involved in metabolism was up-regulated at 30°C in stationary phase, which reflects a slowing of bacterial metabolism in the early stages of its shift to growth at lower temperature followed by an acceleration in the later stages. Conversely, genes up-regulated at 40°C relative to 30°C include those encoding virulence factors such as hemolysins and extracellular secreted proteins with LPXTG motifs. Over-expression of hemolysins was linked to larger zones of hemolysis and enhanced hemolytic activity at 40°C. A key theme identified by our study was that genes involved in purine metabolism and iron acquisition were significantly up-regulated at 40°C. Overall design: Three cultures of GBS grown in rich Todd-Hewitt Yeast extract medium at 30°C and three cultures grown at 40°C served as a source of RNA samples collected at mid-logarithmic phase, late-logarithmic phase, and stationary growth phase. RNA was isolated using a modified Trizol method, and targets for hybridization with custom Affymetrix chip were generated as we have described previously. Genes with 30°C/40°C ratio greater than 2 and less than 0.5 (P value less than 0.05), were considered differentially expressed.