Prevalence and activity of class II microcins in Serratia marcescens strains by isolation source

Serratia marcescens is a highly environmentally adaptable gram-negative bacterium which can be found in both free-living and host-associated lifestyles, where it can function as either a commensal or a pathogen. The diverse array of secreted factors produced by S. marcescens is suggested to facilitate this adaptability. Here, we describe and validate a class of secreted bacteriocins, called class II microcins, which have not previously been described in S. marcescens. Putative class II microcins are found in the majority (96%) of genomes analyzed here, including representative strains from numerous diverse lifestyles. The type of microcin in a given genome has some correspondence to the isolation source of its S. marcescens strain of origin. We demonstrate that heterologous secretion of these microcins can be used to validate their antibacterial activity, yielding 17 confirmed class II microcins from S. marcescens. Testing against a panel of S. marcescens, consisting predominantly of strains pathogenic to humans or insects, shows S. marcescens microcin activity ranges from narrow to broad spectrum. Identifying class II microcins and other factors which may contribute to interbacterial competition or colonization by S. marcescens could inform strategies to prevent S. marcescens infections.

Serratia marcescens is an abundant bacterium in many different environments, but it also represents an important opportunistic pathogen of humans and other animals. Our finding that S. marcescens encodes numerous antibacterial class II microcins is important to understanding factors that may contribute to the lifestyle versatility of this bacterium. Interfering with factors that promote competition or colonization could aid infection prevention.