Transcriptomic analysis of the planktonic growth of Streptococcus pneumoniae serotype 1 reveals serotype-specific gene regulation

Streptococcus pneumoniae is an opportunistic pathogen that colonizes the mucosal surfaces of the human upper respiratory tract. To the exception of very few studies, all previous transcriptomic analyses on the pneumococcus were carried out using lab-adapted strains such as D39 or TIGR4. Our study is one of the first to investigate the transcriptomes of serotype 1 (S1) pneumococci. We took the most basic approach of growing S. pneumoniae in brain heart infusion medium using three distinct strains, i.e. sequence type ST306, ST217 and ST615, as representative isolates of the European, African and South American S1 clusters. As a follow-up to our recent studies on these three lineages, we sought to investigate their respective in vitro transcriptomic profiles in comparison to D39. In total, 292 genes showed significant differential expression in the exponential growth phases of all three S1 isolates compared to D39. A total of 151 genes showed higher transcription levels while 141 genes presented lower expression. The most prominent functional groups showing higher expression included the competence pathway and purine metabolism, while lactose metabolism and iron/amino acid transport presented lower expression in serotype 1 strains. Our study provides novel insight into the signature gene expression associated with hypervirulent pneumococci S1 and highlight the need to perform transcriptomic analysis on pneumococcal strains other than lab-adapted strains. To investigate the Streptococcus S1-specific transcriptional profile we carried out RNA-seq on three S1 strains and one S2 strain over different growth stages and compared the exponential phase samples. *************************************************************** The table below lists GEO accessions reused/reanalyzed for this study. ***************************************************************