title: Indole production provides limited benefit to Escherichia coli during co-culture with Enterococcus faecalis.
abstract: Escherichia coli lives in the gastrointestinal tract and elsewhere, where it coexists within a mixed population. Indole production enables E. coli to grow with other gram-negative bacteria as indole inhibits N-acyl-homoserine lactone (AHL) quorum regulation. We investigated whether E. coli indole production enhanced competition with gram-positive Enterococcus faecalis, wherein quorum signaling is mediated by small peptides. During planktonic co-culture with E. faecalis, the fitness and population density of E. coli tnaA mutants (unable to produce indole) equaled or surpassed that of E. coli wt. During biofilm growth, the fitness of both populations of E. coli stabilized around 100 %, whereas the fitness of E. faecalis declined over time to 85-90 %, suggesting that biofilm and planktonic populations have different competition strategies. Media supplementation with indole removed the competitive advantage of E. coli tnaA in planktonic populations but enhanced it in biofilm populations. E. coli wt and tnaA showed similar growth in Luria-Bertani (LB) broth. However, E. coli growth was inhibited in the presence of filter-sterilized spent LB from E. faecalis, with inhibition being enhanced by indole. Similarly, there was also an inhibition of E. faecalis growth by proteinaceous components (likely bacteriocins) from spent culture media from both E. coli strains. We conclude that E. coli indole production is not a universal competition strategy, but rather works against gram-negative, AHL-producing bacteria.
authors.affiliation: Department of Biology, Texas State University, 601 University Drive, San Marcos, TX, 78666, USA.|McCallum High School, 5600 Sunshine Dr, Austin, TX, 78756, USA.
authors.forename: Shelly L
authors.initials: SL
authors.lastname: Pringle
authors.affiliation: Department of Biological Sciences, University of Texas at Dallas, 800 West Campbell Road, Richardson, TX, 75080, USA.
authors.forename: Kelli L
authors.initials: KL
authors.lastname: Palmer
authors.affiliation: Department of Biology, Texas State University, 601 University Drive, San Marcos, TX, 78666, USA. McLean@txstate.edu.
authors.forename: Robert J C
authors.identifier: http://orcid.org/0000-0002-0610-6143
authors.initials: RJ
authors.lastname: McLean
mesh_terms: D018441:Biofilms; D018920:Coculture Techniques; D013293:Enterococcus faecalis / Q000254:growth & development* / Q000502:physiology; D004926:Escherichia coli / Q000737:chemistry / Q000254:growth & development / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism; D007211:Indoles / Q000378:metabolism*; D015398:Signal Transduction
chemical_list: D029968:Escherichia coli Proteins; D007211:Indoles; C030374:indole
keywords: Colicin; Competition; Enterococcus faecalis; Escherichia coli; Indole; Mixed culture