Mobilomics of toxic/bioactive peptide production in the bloom-forming cyanobacterium Planktothrix

It has been hypothesized that mobile elements induce genomic rearrangements and influence the distribution and functionality of toxic/bioactive peptide synthesis pathways. We performed an in depth genomic analysis by completing the genomes of 13 phylogenetically classified strains of the bloom-forming cyanobacterium Planktothrix spp. to investigate the role of IS elements for seven of such pathways. Though the variation in genome size was positively related to the proportion of IS elements (1.1-3.7% on chromosome), quantitatively IS elements as well as paralogs only had a minor share in genome size variation. Six of seven toxic/ bioactive peptide synthesis gene clusters were found located on the chromosome (i.e. non-ribosomal peptide synthesis (NRPS) of microcystin, anabaenopeptin, aeruginosin, cyanopeptolin, and ribosomal and post-translational peptide synthesis (RiPP) of microviridin, prenylagaramide). For NRPS a high share of SM synthesis gene cluster functionality was observed, while the two RiPP gene clusters were found frequently inactive. Unexpectedly the strains did not show an increased IS element frequency of occurrence in the vicinity of SM synthesis gene clusters. In contrast IS elements occurred with higher proportion in the ten breaking regions related to chromosomal rearrangements related to a localization of toxic/ bioactive peptide synthesis gene clusters on the chromosome.