GSE168986
The Complex Transcriptional Architecture of Magnetosome Operons in Magnetospirillum gryphiswaldense
Magnetosomes are complex membrane organelles synthesized by magnetotactic bacteria (MTB) for navigation in the magnetic field. Their formation is tightly controlled by ?30 specific magnetosome genes arranged in operons. The transcriptional organization of these operons in the model MTB Magnetospirillum gryphiswaldense MSR-1 has been long viewed to be simple, having each a convenient promoter that enable transcription of the operon as a single transcriptional unit. Here, by applying Cappable-seq and whole transcriptome shotgun RNA sequencing, we revealed multiple additional transcription starting sites (TSS) within the magnetosome operons mamABop, mms6op and mamXYop. Using experimental validation by bioluminescence reporter, we demonstrated that most of the new TSS are generated by biologically meaningful promoters. Furthermore, the knockout of the primary promoters in mamABop and mms6op resulted only in mild impairments of the magnetosome formation, suggesting that additional transcripts are indeed generated within these operons. Besides, we identified a strong promoter in the intergenic region within mamXYop, which transcript likely represents a non-coding RNA important for proper expression of the genes in this operon. The promoter sequences from MSR-1 are conservative in most magnetotactic Magnetospirillum spp., but not in other MTB, suggesting the functional conservation in magnetospirilla but independent evolution of the transcription circuits within the magnetosome operons in different phylogenetic groups. Taken together, our data suggest much more complex transcriptional architecture of the magnetosome operons in MSR-1 than deemed before and contribute to unraveling the fundamentals of magnetosome biosynthesis at transcriptional level. Overall design: RNA-Seq of primary transcripts, whole transcriptome and 3'-ends of wild type cells