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Modulation of luminescence operon expression by N-octanoyl-L-homoserine lactone in ainS mutants of Vibrio fischeri.

Abstract：

:Population density-dependent expression of luminescence in Vibrio fischeri is controlled by the autoinducer N-3-oxohexanoyl-L-homoserine lactone (autoinducer 1 [AI-1]), which via LuxR activates transcription of the lux operon (luxICDABEG, encoding the putative autoinducer synthase [LuxI] and the luminescence enzymes). We recently identified a novel V. fischeri locus, ainS, necessary for the synthesis of a second autoinducer, N-octanoyl-L-homoserine lactone (AI-2), which via LuxR can activate lux operon transcription in the absence of AI-1. To define the regulatory role of AI-2, a luxI ainS double mutant was constructed; in contrast to the parental strain and a luxI mutant, the luxI ainS mutant exhibited no induction of luminescence and produced no detectable luminescence autoinducer, demonstrating that V. fischeri makes no luminescence autoinducers other than those whose synthesis is directed by luxI and ainS. A mutant defective only in ainS exhibited accelerated luminescence induction compared with that of the parental strain, indicating that AI-2 functions in V. fischeri to delay luminescence induction. Consistent with that observation, the exogenous addition of AI-2 inhibited induction in a dose-dependent manner in V. fischeri and Escherichia coli carrying the lux genes. AI-2 did not mediate luxR negative autoregulation, alone or in the presence of AI-1, and inhibited luminescence induction in E. coli regardless of whether luxR was under the control of its native promoter or a foreign one. Increasing amounts of AI-1 overcame the inhibitory effect of AI-2, and equal activation of luminescence required 25- to 45-fold-more AI-2 than AI-1. We conclude that AI-2 inhibits lux operon transcription. The data are consistent with a model in which AI-2 competitively inhibits the association of AI-1 with LuxR, forming a complex with LuxR which has a markedly lower lux operon-inducing specific activity than that of AI-1-LuxR. AI-2 apparently functions in V. fischeri to suppress or delay induction at low and intermediate population densities.

journal_name

J Bacteriol

journal_title

Journal of bacteriology

authors

Kuo A,Callahan SM,Dunlap PV

doi

10.1128/jb.178.4.971-976.1996

subject

Has Abstract

pub_date

1996-02-01 00:00:00

pages

971-6

issue

eissn

0021-9193

issn

1098-5530

journal_volume

178

pub_type

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Modulation of luminescence operon expression by N-octanoyl-L-homoserine lactone in ainS mutants of Vibrio fischeri.