Abstract
Chromobacterium haemolyticum is an environmental bacterium that can cause severe and fatal opportunistic infections in humans and animals. Although C. haemolyticum is characterized by its strong β-hemolytic activity, the molecular basis of this phenotype has remained elusive over the more than 15 years since the species was first described. Herein, we report a family of cyclic lipodepsipeptides, the jagaricins, that are responsible for the potent hemolytic activity of C. haemolyticum. Comparative genomics of C. haemolyticum strains revealed a completely conserved gene locus (hml) encoding a nonribosomal peptide synthetase. Metabolic profiling of C. haemolyticum DSM 19808 identified a suite of cyclic lipodepsipeptides as the products, with the three main congeners (jagaricin A-C) being elucidated by a combination of tandem mass spectrometry, chemical derivatization, and nuclear magnetic resonance spectroscopy. Significantly, a C. haemolyticum hml deletion mutant is devoid of hemolytic activity. Moreover, purified jagaricins are hemolytic at low micromolar concentrations in an erythrocyte lysis assay. Further bioassays demonstrated that the cyclic lipodepsipeptides are crucial for the biofilm-forming and swarming behavior of C. haemolyticum. Matrix-assisted laser desorption ionization mass spectrometry imaging showed that primarily jagaricin B and C are involved in these processes in vitro. Our data shed light on the bioactivities of jagaricins, specialized metabolites that likely contribute to both successful niche colonization and the virulence potential of C. haemolyticum.IMPORTANCEDespite the rising incidence of Chromobacterium haemolyticum as a serious opportunistic pathogen, there is limited information on whether the competitive traits that ensure its survival in its freshwater niche also influence host infection. We reveal that C. haemolyticum produces specialized metabolites that not only cause its pronounced hemolytic phenotype but are also crucial for biofilm formation and swarming motility. These results exemplify a case of coincidental evolution, wherein the selective pressures encountered in a primary environmental niche drive the evolution of a trait impacting virulence. This knowledge provides a foundation for the development of antivirulence therapies against the emerging pathogen C. haemolyticum.