title: Detoxification of Indole by an Indole-Induced Flavoprotein Oxygenase from Acinetobacter baumannii.
abstract: Indole, a derivative of the amino acid tryptophan, is a toxic signaling molecule, which can inhibit bacterial growth. To overcome indole-induced toxicity, many bacteria have developed enzymatic defense systems to convert indole to non-toxic, water-insoluble indigo. We previously demonstrated that, like other aromatic compound-degrading bacteria, Acinetobacter baumannii can also convert indole to indigo. However, no work has been published investigating this mechanism. Here, we have shown that the growth of wild-type A. baumannii is severely inhibited in the presence of 3.5 mM indole. However, at lower concentrations, growth is stable, implying that the bacteria may be utilizing a survival mechanism to oxidize indole. To this end, we have identified a flavoprotein oxygenase encoded by the iifC gene of A. baumannii. Further, our results suggest that expressing this recombinant oxygenase protein in Escherichia coli can drive indole oxidation to indigo in vitro. Genome analysis shows that the iif operon is exclusively present in the genomes of A. baumannii and Pseudomonas syringae pv. actinidiae. Quantitative PCR and Western blot analysis also indicate that the iif operon is activated by indole through the AraC-like transcriptional regulator IifR. Taken together, these data suggest that this species of bacteria utilizes a novel indole-detoxification mechanism that is modulated by IifC, a protein that appears to be, at least to some extent, regulated by IifR.
authors.affiliation: Microbial Genetics Laboratory, Department of Microbiology, Tzu-Chi University, Hualien, Taiwan.
authors.forename: Guang-Huey
authors.initials: GH
authors.lastname: Lin
authors.affiliation: Department of Biochemistry, School of Medicine, Tzu-Chi University, Hualien, Taiwan.
authors.forename: Hao-Ping
authors.initials: HP
authors.lastname: Chen
authors.affiliation: Department of Bioscience Technology, Chang Jung Christian University, Tainan, Taiwan.
authors.forename: Hung-Yu
authors.initials: HY
authors.lastname: Shu
mesh_terms: D040981:Acinetobacter baumannii / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D015153:Blotting, Western; D049308:Dioxygenases / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D005420:Flavoproteins / Q000235:genetics / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial / Q000187:drug effects; D007203:Indigo Carmine / Q000378:metabolism*; D007211:Indoles / Q000378:metabolism* / Q000494:pharmacology; D050296:Microbial Viability / Q000187:drug effects / Q000235:genetics; D008969:Molecular Sequence Data; D009154:Mutation; D009876:Operon / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017386:Sequence Homology, Amino Acid
chemical_list: D001426:Bacterial Proteins; D005420:Flavoproteins; D007211:Indoles; C030374:indole; D007203:Indigo Carmine; D049308:Dioxygenases; C021440:indole-2,3-dioxygenase