Synechococsins: Lanthipeptides acting as defensive signals to disarm offensive competitors?

Synechococsins represent a diverse group of class II lanthipeptides from the prochlorosin family, produced by the marine picocyanobacterium Synechococcus. A single strain can produce multiple SyncA peptides through modification by SyncM, a bifunctional lanthipeptide synthetase. Despite the prevalence of these lanthipeptides in nature, their biological functions remain elusive, even for the most studied group, Prochlorococcus MIT9313. This study investigated the transcriptomic response of the marine SyncA-producing strain Synechococcus sp. RS9116 to the characterized and purified SyncA6 peptide from Synechococcus sp. MITS9509. Intriguingly, the analysis of gene expression revealed a strong down-regulation of genes that encode putative ribosomally produced antimicrobial peptides, such as coculture-responsive genes (CCRG-2) and microcin-C-like bacteriocins. This study suggests a potential biological role for synechococsins as interspecific gene modulators, improving the fitness of the producing strain in a competitive and resource-limited environment.