The latest World Health Organization (WHO) report stated that multi-drug-resistant (MDR) bacteria directly cause 1.27 million deaths worldwide. Lanthipeptides have great potential as biotherapeutics as an innovative way to combat antimicrobial resistance (AMR). High-throughput sequencing, genome mining methods, and synthetic biology have facilitated the discovery and characterization of promiscuous posttranslational modification enzymes (PTM). Promiscuous PTM enzymes can be applied as synthetic tools to bioengineered lanthipeptides and create new bioactive molecules. In this thesis, we characterized a new promiscuous lanthipeptide synthetase from Synechococcus MIT9509 called SyncM. SyncM belongs to ProcM-like enzymes capable of modifying several different substrates (SyncA). The developed lanthipeptide expression system adds SyncM to the RiPP-engineering toolbox of Lactococcus lactis. The expression of SyncA substrates and bioengineering studies highlighted this system’s ability to form large rings and yielded insights into SyncM’s processing. All the information collected in these thesis chapters can be applied to aid future bioengineering studies for lanthipeptide bioengineering. Finally, we also investigated the possible biological roles of these synechococsins (SyncAs) by a description of their genomic landscape and by transcriptomics analysis.