High-quality transcriptome profile of Treponema pallidum subsp. pallidum: confirmation of transcriptional landscape

Syphilis remains a critical global health challenge due to its potential for severe complications and the increase in its incidence rate over recent years. Until recently, the infectious agent of syphilis, Treponema pallidum subsp. pallidum (TPA), could not be cultured in vitro. Advances in co-culture techniques have finally allowed for effective long-term cultivation of TPA, providing a platform to study its biology. Limited transcriptional data from TPA have been reported so far and many genes in treponemal genomes are annotated based on in silico prediction of putative coding sequences without functional validation. To inform future syphilis vaccine development, experimental validation of in silico predicted genes coupled with functional annotation is necessary. In this study, strand-specific RNA-sequencing was used to reconstruct a high-quality transcriptome profile of TPA, confirming the active transcription of genes previously annotated as hypothetical, paving the way for more accurate identification of vaccine target candidates. Our transcriptomic data also revealed, for the first time, the organization of genes into transcription units, an abundance of anti-sense RNAs, and transcripts from intergenic regions, providing crucial insights for future functional genomics studies of TPA. Author SummaryIn our study, we explored the genetic activity of the bacteria responsible for syphilis, Treponema pallidum subsp. pallidum (TPA). Although syphilis has been a known disease for centuries, the bacterium causing it has remained difficult to study because it couldnt be easily grown in the lab. Recently, new techniques have allowed us to cultivate TPA successfully, enabling deeper investigation into its genetics. By employing directional RNA sequencing, we have mapped out which genes are actively transcribed, including those previously labeled as hypothetical. Our study has also revealed new insights into the gene organization and uncovered the presence of antisense RNA, which may regulate gene expression. These findings offer critical information that could inform future research and vaccine development efforts for syphilis.