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Related Experiment Video

Updated: Jul 8, 2026

In Situ Measurement and Correlation of Cell Density and Light Emission of Bioluminescent Bacteria
05:52

In Situ Measurement and Correlation of Cell Density and Light Emission of Bioluminescent Bacteria

Published on: June 28, 2018

LuxG is a functioning flavin reductase for bacterial luminescence.

Sarayut Nijvipakul1, Janewit Wongratana, Chutintorn Suadee

  • 1Department of Biochemistry and Center for Excellence in Protein Structure and Function, Faculty of Science, Mahidol University, Bangkok 10400, Thailand.

Journal of Bacteriology
|December 25, 2007
PubMed
Summary

The luxG gene product, LuxG, functions as a flavin reductase, supplying reduced flavin mononucleotide (FMNH-) essential for bacterial bioluminescence. LuxG is confirmed as the primary in vivo source of FMNH- for light emission.

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Area of Science:

  • Biochemistry
  • Molecular Biology
  • Microbiology

Background:

  • The luxG gene is part of the lux operon in marine luminous bacteria.
  • LuxG has been hypothesized to be a flavin reductase supplying reduced flavin mononucleotide (FMN) for bacterial luminescence, but its function remained uncharacterized due to expression and characterization challenges.

Purpose of the Study:

  • To clone, express, and characterize the luxG gene product from Photobacterium leiognathi TH1.
  • To establish the biochemical properties and enzymatic activity of LuxG as a flavin reductase.
  • To determine the in vivo significance of LuxG in bacterial bioluminescence.

Main Methods:

  • Cloning and expression of luxG in Escherichia coli (native and His6-tagged forms).
  • Purification and biochemical characterization of recombinant LuxG.
  • Enzymatic assays using NADH or NADPH and FMN, kinetic analysis (Lineweaver-Burk plots, steady-state kinetics), and coupled assays with luciferases.
  • Construction and analysis of a luxG gene knockout mutant in P. leiognathi TH1.

Main Results:

  • Recombinant LuxG was successfully expressed, purified, and characterized as a homodimeric protein without a bound prosthetic group.
  • LuxG demonstrated flavin reductase activity, catalyzing the oxidation of NADH (preferred substrate) in the presence of FMN.
  • Kinetic analysis revealed LuxG follows a ternary-complex model with specific kinetic parameters (Km for NADH: 15.1 µM, Km for FMN: 2.7 µM, kcat: 1.7 s⁻¹ at 4°C, pH 8.0).
  • In vitro assays confirmed LuxG supplies FMNH- for luciferase activity.
  • A luxG knockout mutant of P. leiognathi TH1 exhibited significantly reduced luminescence, indicating LuxG's crucial role in vivo.

Conclusions:

  • LuxG functions as a flavin reductase, essential for providing reduced flavin mononucleotide (FMNH-) for bacterial bioluminescence.
  • LuxG is the predominant source of FMNH- required for the in vivo luminescence reaction in Photobacterium leiognathi.
  • This study successfully characterized LuxG, confirming its role in the bioluminescence pathway.