Modulation of luminescence operon expression by N-octanoyl-L-homoserine lactone in ainS mutants of Vibrio fischeri
Modulation of luminescence operon expression by N-octanoyl-L-homoserine lactone in ainS mutants of Vibrio fischeri
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DOI：
10.1128/jb.178.4.971-976.1996
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发表时间：
1996-02-01
影响因子：
3.2
通讯作者：
Dunlap, PV
中科院分区：
文献类型：
--
作者：
Kuo, A;Callahan, SM;Dunlap, PV
在费氏弧菌中发光的群体密度依赖性表达由自诱导物N-3-氧代己酰-L-高丝氨酸内酯（自诱导物1 [AI-1]）控制，其通过LuxR激活lux操纵子（luxICDABEG，编码推定的自诱导物合酶[LuxI]和发光酶）的转录。我们最近鉴定了一种新的费氏弧菌基因座，ainS，是合成第二种自诱导物N-辛酰基-L-高丝氨酸内酯（AI-2）所必需的，AI-2通过LuxR可以在缺乏AI-1的情况下激活lux操纵子转录。为了确定AI-2的调节作用，构建了一个luxI ainS双突变体;与亲本菌株和luxI突变体相比，luxI ainS突变体没有表现出发光诱导作用，也没有产生可检测到的发光自诱导物，这表明费氏弧菌除了由luxI和ainS指导合成的发光自诱导物外，不产生发光自诱导物。与亲本菌株相比，仅ainS缺陷的突变体表现出加速的发光诱导，表明AI-2在费氏弧菌中起延迟发光诱导的作用。与该观察结果一致，在携带luxI基因的费氏弧菌和大肠杆菌中，外源添加AI-2以剂量依赖性方式抑制诱导，AI-2不介导luxR负性自身调节，单独或在AI-I存在下，抑制E.无论luxR是在其天然启动子还是外源启动子的控制下，都能在大肠杆菌中表达。增加量的AI-1克服了AI-2的抑制作用，并且发光的相等激活需要比AI-1多25至45倍的AI-2。我们得出结论，AI-2抑制lux操纵子转录。数据与AI-2竞争性抑制AI-1与LuxR结合的模型一致，与LuxR形成复合物，该复合物具有比AI-1-LuxR显著更低的lux操纵子诱导比活性。AI-2在费氏弧菌中的功能显然是在低和中等种群密度下抑制或延迟诱导。
Population density-dependent expression of luminescence in Vibrio fischeri is controlled by the autoinducer N-3-oxohexanoyI-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 od 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 luxI genes, AI-2 did not mediate luxR negative autoregulation, alone or in the presence of AI-I, 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-I, 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-I 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.