Single cell analysis evidence Heterogeneous expression of the Agr communication system of Listeria monocytogenes
Résumé
Communication, often referred as Quorum Sensing, is involved in the adaptation of most bacteria to their environment. In the genus Listeria, the agr communication system affects the biology of Listeria monocytogenes during saprophytic life (biofilm formation) and during infection. In the present study, we investigated in situ agr expression of six isolates of L. monocytogenes by combining gfp reporters, flow cytometry and fluorescent microscopy during plantonic growth and dynamic flow cell biofilm set ups. Unexpectedly, during growth in TSB homogenised liquid cultures incubated at 25°C, while auto-inducer concentration was uniform, statistically significant results showed that two distinct sub-populations existed within cultures of the six isolates and the percentage of AGR-ON cells ranged from 15% to 73% according to the isolate tested. At 37°C, it varied from 15% to 48%. Finally, in flow cells, 69% to 80% of the cells of 24 h biofilms expressed Agr but these differences were not significant. Our results highlight the need to integrate individuality of bacteria in order to decipher the mechanisms of Listeria monocytogenes adaptation to its environment.