Novel intercellular communication system in Escherichia coli that confers antibiotic resistance between physically separated populations

AIMS: To determine whether intercellular signalling can occur between physically separated populations of Escherichia coli. METHODS AND RESULTS: Intercellular signalling between physically discrete populations of E. coli BL21 was analysed in bi-partite Petri dishes. Transfer of a growth-promoting signal resulted in induction of resistance to the antibiotic ampicillin. Optimal expression of the signal occurred when the signalling population was established as a bacterial lawn for 24 h. This represented an entry into the stationary phase of growth, as indicated by the expression profile of the RNA polymerase subunit sigma38 (sigmaS; sigma S). The growth-promoting effect was also observed when E. coli DH5alpha (luxS-) was used as the signalling population. Preventing passage of air between the two populations resulted in a complete cessation of the growth-promoting effect. CONCLUSIONS: A growth-promoting signal occurs between physically separated cultures of E. coli. The exact nature of the signal remains to be determined but does not involve the production of autoinducer-2 from the luxS gene. Signal transmission is likely to involve airborne transfer of a signal species. SIGNIFICANCE AND IMPACT OF THE STUDY: Intercellular signalling systems exist in bacteria that enable antibiotic resistance to be conferred between physically separated populations.