SYNERGISTIC HEMOLYSIS IN “NON-HEMOLYTIC” BACTEROIDES SPECIES

Abstract

Bacteroides is a genus of anaerobic bacteria that are often found in high abundance in the human colon. They have a complex relationship with their human host, conferring health benefits as members of the gut microbiota but also acting as opportunistic pathogens. Though many of the virulence factors in Bacteroides have been characterized, it is currently classified as nonhemolytic. Work with Bacteroides isolates led to the observation, by happenstance, of unexpected hemolytic activity in multiple species. After incubation on blood agar plates, we observed that some isolates were clearly hemolytic, but only when plated in close proximity to certain, ‘activating’ isolates. We performed a systematic screen for hemolytic activity on a library of 94 Bacteroides isolates and identified one which was able to activate hemolysis in 30% of the collection. Using timelapse photography, we show this zone of hemolysis begins between the two colonies and proceeds in a retrograde fashion towards the ‘activated’ colony. The asymmetrical patterns of hemolysis are unlike any bacterial synergy reported to date. To investigate the mechanism behind this pattern, we combined a comparative genomics and mutagenesis approach to narrow down the genetic basis of this phenotype. Here, we characterize a unique synergistic hemolysis phenotype in Bacteroides, a genus of bacteria currently classified as nonhemolytic. This novel phenotype may provide further insight into Bacteroides as an opportunistic pathogen and may have uncovered a new mechanism by which they interact.