When Survival Turns into Pathogenicity: How Evolution Equips an Environmental Bacterium to Harm Humans

Microverse researchers uncover dual-use virulence factors in Chromobacterium haemolyticum

A team of researchers affiliated with the "Balance of the Microverse" Cluster of Excellence at the University of Jena has discovered how a harmless environmental bacterium can become a dangerous pathogen. The study, conducted by Principal Investigator Christian Hertweck and his team at the Leibniz-HKI in collaboration with scientists from the University of Melbourne, reveals how natural compounds produced by Chromobacterium haemolyticum promote both ecological fitness and severe disease. The findings were recently published in the journal mBio.

“Chromobacterium haemolyticum is typically an innocuous environmental microbe,” explains microbiologist Ingrid Richter, co-lead author of the study. “But under the right – or rather wrong – conditions, it can cause life-threatening infections in humans and animals. Until now, it was unclear which factors are responsible for its virulence.”

The team identified a group of natural products called cyclic lipodepsipeptides – including the known antifungal jagaricin and two newly described variants, jagaricin B and C – as key players. These molecules not only destroy red blood cells, but also contribute to the bacterium’s ability to form biofilms and expand through swarming motility. In doing so, they serve as what the researchers call dual-use virulence factors: traits that evolved for survival in the environment but inadvertently enable infection in animal hosts.

Targeted genetic deletions confirmed the importance of these molecules. Mutant strains of the bacterium that lack the gene cluster responsible for jagaricin production no longer exhibit haemolysis, nor do they show biofilm formation or swarming behavior. This suggests that the compounds are crucial for both ecological success and pathogenic potential.