Diffusion of autoinducer is involved in regulation of the Vibrio fischeri luminescence system

Abstract

The enzymes for luminescence in Vibrio fischeri are induced by the accumulation of a species-specific metabolite (autoinducer) in the culture medium. Tritium-labeled auteinducer was used to study the mechanism of autoinduction. When 3H-autoinducer was added to suspensions of V. fischeri or Escherichwa coli, cellular concentrations equaled external concentrations. For V. fischeri, equilibration of 3H-autoinducer was rapid (within 20 s), and >90% of the cellular tritium remained in unmodified autoinducer. When V. fischeri or E. coli cells containing 3H-autoinducer were transferred to autoinducer-free buffer, 85 to 99.5% of the radiotracer escaped from the cells, depending on the strain. Concentrations of autoinducer as low as 10 nM, which is equivalent to 1 or 2 molecules per cell, were sufficient for induction, and the maximal response to autoinducer occurred at about 200 nM. If external autoinducer concentrations were decreased to below 10 nM after induction had commenced, the induction response did not continue. Based on this study, a model for autoinduction is described wherein autoinducer association with cells is by simple diffusion and binding of autoinducer to its active site is reversible.

Dynamic regulation ofN-acyl-homoserine lactone production and degradation inPseudomonas putidaIsoF

“…Thus, the autoinducersensing mechanism of P. putida includes a positive feedback (leading to a coordination of the bacterial cells), even though it is not very strong under the given conditions. The threshold value of 70 nmol L À1 is located in the range of threshold concentrations, as reported previously in the literature (Kaplan & Greenberg, 1985;Gray & Greenberg, 1992).…”

“…In our example, the production rate increased by one order of magnitude when exceeding the threshold, which was rather weak. For other species, increases of production rates between factors of 10 and 10 000 were reported (Kaplan & Greenberg, 1985;Steidle et al, 2002), and so the parameter value here fits within that range. Thus, the autoinducersensing mechanism of P. putida includes a positive feedback (leading to a coordination of the bacterial cells), even though it is not very strong under the given conditions.…”

Mechanism for iron control of the Vibrio fischeri luminescence system: Involvement of cyclic AMP and cyclic AMP receptor protein and modulation of DNA level

“…4) and pre-sumably produce more LuxR protein. Induction of 1uxICDABEG transcription occurs at the point in culture growth when a critical concentration of autoinducer has accumulated (Eberhard, 1972;Eberhard et al, 198 1 ;Kaplan and Greenberg, 1985;Nealson, 1977). The position of ZuxI (putative autoinducer synthetase gene) in the IuxICDABEG operon places it under positive feedback control (Eberhard et al, 1991;Engebrecht et al, 1983;Friedrich and Greenberg, 1983).…”

“…Induction of luminescence in Vibrio Jischeri is controlled by the cell density-dependent accumulation of a species-specific, diffusible autoinducer produced by V. jischeri (N-[3-oxohexanoyl] homoserine lactone) (Eberhard, 1972;Eberhard et al, 1981Eberhard et al, , 1986Eberhard et al, ,1991Kaplan and Greenberg, 1985;Nealson, 1977;Rosson and Nealson, 1981). During growth of V. jischeri cells in batch culture, autoinducer gradually accumulates in the medium and in cells.…”

“…The level of autoinducer is the key factor determining the OD at which a culture induces luminescence (Eberhard, 1972;Eberhard et al, 1981;Kaplan and Greenberg, 1985;Nealson, 1977;Rosson and Nealson, 1981). Recently, we developed a sensitive method for assaying autoinducer based on the response of an E. coli strain containing the lux genes with a non-polar point mutation in lux1 (Dunlap and Ray, 1989).…”