The Effects of Quorum Sensing on the Growth and Luminescence of the Baterium Vibrio fischeri

The mutualistic system between the luminescent bacteria Vibrio fischeri and its host the sepiolid squid, is one of the most studied in biology. There is a difference of brightness between various bacterial strains within the host, some bright and some extremely dim. Previous research has suggested that the difference between bright and dim strains is their production of quorum-sensing signals. This leads to the formulation of the hypothesis that bright and dim strains will respond differently to exogenously added metabolites that are quorum-sensing signals. To test the hypothesis we added quorum-sensing signals (3-oxo-C6-HSL and C8-HSL) to pairs of bright and dim strains of 3 different hosts from the species, Euprymna scolopes, Euprymna tasmanica and Sepiola affinis.  We found significant differences between bright and dim strains within each pair in response to C8-HSL. Most bright strains did not respond to C8-HSL, while most dim strains increased luminescence in response. Unexpectedly, in strains from the S. affinis host, addition of C8 HSL and 3-oxo-C6-HSL decreased luminescence. In strains from both Euprymna species the addition of both quorum sensing molecules increased or had no effect on luminescence. These results indicate that within a single species of bacteria, response to quorum sensing signals varies widely. Supported by NIH Grant #R25 GM048998-13 and 5G12RR008124.