Global profiling of Streptococcus pneumoniae gene expression at different growth temperatures

Streptococcus pneumoniae is a common commensal of the upper respiratory tract of healthy humans and is an important pathogen in young children, immunocompromised adults, and the elderly. To better understand the strategies employed by this bacterial species in adapting to conditions present at different infection sites in the host, global transcription profiling was used to study gene expression at different growth temperatures: 21, 29, 33, 37, and 40 °C. Here, we found that 658 genes (29%) out of 1717 genes were differently expressed (≥1.5-fold change) in at least one growth temperature relative to 37°C. The percentages of genes whose expression was altered in each growth temperature, respectively, were: 21°C: 53% ↑, 47% ↓ 29°C: 44% ↑, 56% ↓; 33°C: 27% ↑, 73% ↓ and 40°C: 44% ↑, 56% ↓. Hierarchical clustering (HC) of the temperature regulated genes resulted in four clusters, namely A-D of differently expressed genes grouped by bacterial growth temperature. Cluster A represented 81 genes reflecting enhanced expression at 33°C. Cluster B included 260 genes whose expression increased with growth temperature. Cluster C had 28 genes with 68% showing enhanced expression at 29°C while cluster D had 289 genes with 74% genes showing enhanced expression at 21°C relative to 37°C. Principal component (PC) analysis also divided differentially expressed genes into four groups and was highly correlated with HC, suggesting that temperature regulated expression is not random but coordinated. Overall, these results indicated substantial reprogramming of transcription in response to growth temperature. Functional characterization of differential gene expression at different temperatures provides further information on the molecular mechanism(s) that allows S. pneumoniae to adapt to various host environments.