Utilises Colicins During Inter-bacterial Competition

The mammalian colon is one of the most densely populated habitats currently recognised, with 10-10 commensal bacteria per gram of colonic contents. Enteric pathogens must compete with the resident intestinal microbiota to cause infection. Among these enteric pathogens are species which cause approximately 125 million infections annually, of which over 90 % are caused by and was previously reported to use a Type VI Secretion System (T6SS) to outcompete and in and experiments. strains have also been reported to harbour colicinogenic plasmids, which are an alternative anti-bacterial mechanism that could provide a competitive advantage against the intestinal microbiota. We sought to determine the contribution of both T6SS and colicins to the anti-bacterial killing activity of . We reveal that whilst the T6SS operon is present in there is evidence of functional degradation of the system through SNPs, indels and IS within key components of the system. We created strains with synthetically inducible T6SS operons but were still unable to demonstrate anti-bacterial activity of the T6SS. We demonstrate that the anti-bacterial activity observed in our assays was due to colicin activity. We show that no longer displayed anti-bacterial activity against bacteria that were resistant to colicins, and removal of the colicin plasmid from abrogated anti-bacterial activity of . We propose that the anti-bacterial activity demonstrated by colicins may be sufficient for niche competition by within the gastrointestinal environment.