The role of contact-dependent growth inhibition toxin systems in bacterial competition and biofilm development

Contact-dependent growth inhibition (CDI) toxins are a recently identified family of polymorphic toxins, initially found in Escherichia coli. CDI toxins are found widely spread in Gram-negative bacterial species, including pathogenic strains, and have been shown to possess a wide range of toxin types which are effective against other bacteria. This research shows that the E. coli EC93 CDI system confers a competitive advantage on bacteria growing in multi strain biofilms with susceptible bacteria. This advantage is due to two factors, firstly the EC93 CDI toxin was shown to be capable of inhibiting the growth of susceptible bacteria in a biofilm and secondly the conserved region of the EC93 CdiA protein was found to increase the rate of biofilm formation. Analysis of the effects of the EC93 and EC869o11 CDI toxins at the single cell level showed that different classes of CDI toxins can act at different rates and with varying degrees of reversibility. Understanding the variable impact of CDI toxins, in concert with CDI’s role in enhancing biofilm formation, aids our understanding of bacterial competition in the natural environment.