Bacterial bioluminescence. Comparisons of bioluminescence emission spectra, the fluorescence of luciferase reaction mixtures, and the fluorescence of flavin cations

The Sensitized Bioluminescence Mechanism of Bacterial Luciferase

After more than one-half century of investigations, the mechanism of bioluminescence from the FMNH₂ assisted oxygen oxidation of an aliphatic aldehyde on bacterial luciferase continues to resist elucidation. There are many types of luciferase from species of bioluminescent bacteria originating from both marine and terrestrial habitats. The luciferases all have close sequence homology, and in vitro, a highly efficient light generation is obtained from these natural metabolites as substrates. Sufficient exothermicity equivalent to the energy of a blue photon is available in the chemical oxidation of the aldehyde to the corresponding carboxylic acid, and a luciferase-bound FMNH-OOH is a key player. A high energy species, the source of the exothermicity, is unknown except that it is not a luciferin cyclic peroxide, a dioxetanone, as identified in the pathway of the firefly and the marine bioluminescence systems. Besides these natural substrates, variable bioluminescence properties are found using other reactants such as flavin analogs or aldehydes, but results also depend on the luciferase type. Some rationalization of the mechanism has resulted from spatial structure determination, NMR of intermediates and dynamic optical spectroscopy. The overall light path appears to fall into the sensitized class of chemiluminescence mechanism, distinct from the dioxetanone types.

Perspectives on Bioluminescence Mechanisms

The molecular mechanisms of the bioluminescence systems of the firefly, bacteria and those utilizing imidazopyrazinone luciferins such as coelenterazine are gradually being uncovered using modern biophysical methods such as dynamic (ns-ps) fluorescence spectroscopy, NMR, X-ray crystallography and computational chemistry. The chemical structures of all reactants are well defined, and the spatial structures of the luciferases are providing important insight into interactions within the active cavity. It is generally accepted that the firefly and coelenterazine systems, although proceeding by different chemistries, both generate a dioxetanone high-energy species that undergoes decarboxylation to form directly the product in its S₁ state, the bioluminescence emitter. More work is still needed to establish the structure of the products completely. In spite of the bacterial system receiving the most research attention, the chemical pathway for excitation remains mysterious except that it is clearly not by a decarboxylation. Both the coelenterazine and bacterial systems have in common of being able to employ "antenna proteins," lumazine protein and the green-fluorescent protein, for tuning the color of the bioluminescence. Spatial structure information has been most valuable in informing the mechanism of the Ca²⁺ -regulated photoproteins and the antenna protein interactions.

Characterization of an anthraquinone fluor from the bioluminescent, pelagic polychaete Tomopteris

Tomopteris is a cosmopolitan genus of polychaetes. Many species produce yellow luminescence in the parapodia when stimulated. Yellow bioluminescence is rare in the ocean, and the components of this luminescent reaction have not been identified. Only a brief description, half a century ago, noted fluorescence in the parapodia with a remarkably similar spectrum to the bioluminescence, which suggested that it may be the luciferin or terminal light-emitter. Here, we report the isolation of the fluorescent yellow–orange pigment found in the luminous exudate and in the body of the animals. Liquid chromatography-mass spectrometry revealed the mass to be 270 m/z with a molecular formula of C₁₅H₁₀O₅, which ultimately was shown to be aloe-emodin, an anthraquinone previously found in plants. We speculate that aloe-emodin could be a factor for resonant-energy transfer or the oxyluciferin for Tomopteris bioluminescence.

Blue light kills Aggregatibacter actinomycetemcomitans due to its endogenous photosensitizers

OBJECTIVES

The aim of this study was to demonstrate that the periodontal pathogen Aggregatibacter actinomycetemcomitans (AA) can be killed by irradiation with blue light derived from a LED light-curing unit due to its endogenous photosensitizers.

MATERIALS AND METHODS

Planktonic cultures of AA and Escherichia coli were irradiated with blue light from a bluephase® C8 light-curing unit with an emission peak at 460 nm, which is usually applied for polymerization of dental resins. A CFU-assay was performed for the analysis of viable bacteria after treatment. Moreover, bacterial cells were lysed and the lysed AA and E. coli were investigated for generation of singlet oxygen. Spectroscopic measurements of lysed AA and E. coli were performed and analyzed for characteristic absorption and emission peaks.

RESULTS

A light dose of 150 J/cm(2) induced a reduction of ≥5 log10 steps of viable AA, whereas no effect of blue light was found against E. coli. Spectrally resolved measurements of singlet oxygen luminescence showed clearly that a singlet oxygen signal is generated from lysed AA upon excitation at 460 nm. Spectroscopic measurements of lysed AA exhibited characteristic absorption and emission peaks similar to those of known porphyrins and flavins.

CONCLUSIONS

AA can be inactivated by irradiation with blue light only, without application of an exogenous photosensitizer.

CLINICAL RELEVANCE

These results encourage further studies on the potential use of these blue light-mediated auto-photosensitization processes in the treatment of periodontitis for the successful inactivation of Aggregatibacter actinomycetemcomitans.

Bacterial bioluminescence: Spectral study of the emitters in the in vitro reaction

Transient fluorescent species are observed in the bioluminescent reactions of three reduced flavin mononucleotides with aliphatic aldehydes and oxygen, catalyzed by bacterial luciferase. In each case the fluorescence spectral distribution is similar to that of the bioluminescence but is readily distinguishable from it on the basis of a significantly greater signal strength. The corrected bioluminescence maxima using Beneckea harveyi luciferase are 479 nm (iso-FMNH(2)), 490 nm (FMNH(2)), and 560 nm (2-thio-FMNH(2)). In an ethanol glass at 77 K, 2-thioriboflavin is fluorescent (varphi(F) = 0.03, lambda(max) = 562 nm). These results are interpreted by a sensitized chemiluminescence mechanism in which the flavins bound to luciferase act as acceptors of excitation energy. For 2-thio-FMNH(2), this acceptor species appears to be the oxidized 2-thio-FMN on the basis of the spectral evidence, whereas for the other flavins, some form of reduced species is a more likely candidate.

Isolation of the in vivo emitter in bacterial bioluminescence

A blue fluorescence protein has been isolated and purified from extracts of the luminous bacterium Photobacterium phosphoreum. It is a single polypeptide of molecular weight 22,000 with absorption maxima at 274 and 418 nm. It is efficiently fluorescent (varphi(F) 0.45), with a fully corrected spectral maximum (476 nm) and distribution identical to the in vivo bioluminescence from this same type of bacterium. At low concentration this fluorescence shifts towards the red and becomes identical to the in vitro bioluminescence emission. This spectral shift apparently results from a change in the protein pulled by dissociation of the chromophore (K(d) [unk] 10(-7) M). If the blue fluorescence protein is included in the in vitro bioluminescence reaction with reduced FMN, oxygen, aldehyde, and luciferase (P. phosphoreum), the bioluminescence spectrum is shifted towards the blue from its maximum at 490 nm to one at 476 nm, where it is again identical in all respects to the in vivo bioluminescence spectrum. This is accompanied by an increase in the initial light intensity by an order of magnitude at saturating levels of blue fluorescence protein, and the specific light yield of the luciferase is increased 4-fold. It is suggested that the blue fluorescence protein acts as a sensitizer of the bacterial bioluminescence reaction.

Comparison of the spectral emission of lux recombinant and bioluminescent marine bacteria

The purpose of the present paper was to study the influence of bacteria harbouring the luciferase-encoding Vibrio harveyi luxAB genes upon the spectral emission during growth in batch-culture conditions. In vivo bioluminescence spectra were compared from several bioluminescent strains, either naturally luminescent (Vibrio fischeri and Vibrio harveyi) or in recombinant strains (two Gram-negative Escherichia coli::luxAB strains and a Gram-positive Bacillus subtilis::luxAB strain). Spectral emission was recorded from 400 nm to 750 nm using a highly sensitive spectrometer initially devoted to Raman scattering. Two peaks were clearly identified, one at 491-500 nm (+/- 5 nm) and a second peak at 585-595 (+/- 5 nm) with the Raman CCD. The former peak was the only one detected with traditional spectrometers with a photomultiplier detector commonly used for spectral emission measurement, due to their lack of sensitivity and low resolution in the 550-650 nm window. When spectra were compared between all the studied bacteria, no difference was observed between natural or recombinant cells, between Gram-positive and Gram-negative strains, and growth conditions and growth medium were not found to modify the spectrum of light emission.

Bacterial luminescence: luminescence mechanism with cyclic peroxide participation and dependence on reactive oxygen species (a hypothesis)

Chemically initiated exchange (CIEE) luminescence reactions were reviewed and a new mechanism of luminescence with peracid as an intermediate is proposed; bacterial luminescence is generally considered to be a case of dioxetane luminescence, or, to be more precise, CIEE-luminescence which includes the generation of a cyclic peroxide. In the hypothesis the monooxygenase reaction (aldehyde -->fatty acid) should not be coupled with emitter generation as is usually believed, but only with the generation of peracid. As to the generation of the emitter, excited flavin, it is likely to occur later, during the interaction of flavin with cyclic peroxide. Its consequence is the breaking of two chemical bonds (O-O and C-C) in the cyclic peroxide and simultaneous generation of 4alpha-hydroxyflavin in exited state. In general, the generation of light includes three stages: 1) the monooxygenase reaction and the concurrent production of peracid; 2) the conversion of peracid to cyclic peroxide; and 3) the interaction of cyclic peroxide with flavin (through the CIEE mechanism).

The spectral characteristics of luminous marine organisms

Measurements of the bioluminescent emission spectra of a wide range of marine animals demonstrate considerable differences between taxa in both the position of the peak emission and the half bandwidth. Although most of the measured spectra are unimodal, some species have either two peaks or one main peak with subsidiary shoulders. Such structured emission spectra are present in several systematic groups and in some cases the emission characteristics have been observed to vary with time. The emission maxima of most species fall within the range 450—490 nm, though maxima from 395-545 nm have been recorded. Species found in the pelagic environment are mostly blue-emitting but there is some indication of relative increase in green-emitting species in the benthic environment. Terrestrial organisms are predominantly yellow-green luminescent. The ecological value of the observed spectral differences is discussed. While the characteristics of the emission spectra have considerable adaptive value for certain functions, some minor spectral variations may not be of ecological significance. Selection for increased quantum efficiency of the luminescence may sometimes predominate over spectral considerations.

Bioluminescence decay kinetics in the reaction of bacterial luciferase with different aldehydes

At 22 degrees C the bioluminescence decay kinetics in the in vitro reaction catalysed by Vibrio harveyi luciferase in the presence of different aldehydes--nonanal, decanal, tridecanal and tetradecanal did not follow the simple exponential pattern and could be fitted to a two-exponential process. One more principal distinction from the first-order kinetics is the dependence of the parameters on aldehyde concentration. The complex bioluminescence decay kinetics are interpreted in terms of a scheme, where bacterial luciferase is able to perform multiple turnovers using different flavin species to produce light. The initial phase of the bioluminescent reaction appears to proceed mainly with fully reduced flavin as the substrate while the final one results from the involvement of flavin semiquinone in the catalytic cycle.

Kinetic characteristics of calcium-dependent, cholinergic receptor controlled ATP secretion from adrenal medullary chromaffin cells

Adrenal chromaffin cells secrete catecholamines (CA) and ATP in response to acetylcholine (ACh) and high [K+]o. The release process is relatively fast making it difficult to measure the early phase of the secretory response. Recently we were able to resolve the time course of the secretory response by measuring the release of ATP using luciferin-luciferase included in the extracellular medium. For the three secretagogues studied, ACh, nicotine and high [K+]o, the early phase of release followed a complex kinetics. Allowing for an initial delay of the secretory response, the kinetics could be described as the sum of two power exponential processes. Increasing the temperature from 23 to 37 degrees C induced a marked decrease in the two time constants needed to fit the early time course of the ATP secretion. The activation energies, estimated from Arrhenius plots, were approx. 20 and 16 kcal/mol for both phases of ATP release induced by either cholinergic agonists or high [K+]o. These results suggest that cholinergic receptor activation and membrane depolarization induce ATP (and CA) secretion through a common pathway. The initial delay in the onset of the secretory response decreased with increasing doses of secretagogue and with temperature. We propose that the delay preceding the actual onset of ATP release represents the time required for generation of intracellular second messengers. The effective concentration attained by these messengers depend apparently on both receptor occupancy by the agonist and the ensuing Ca2+ channel activation.

Bioluminescence emission of bacterial luciferase with 1-deaza-FMN. Evidence for the noninvolvement of N(1)-protonated flavin species as emitters

The reaction of reduced 1-d-FMN with oxygen and decanal results in bioluminescence with kinetic and spectral properties similar to those of the reaction with FMNH2, even though the spectral (absorbance, fluorescence) and chemical properties of the oxidized forms differ greatly. This emission, which is about 10-15% as efficient as with FMNH2, is postulated to involve the intermediacy of the corresponding 4a-hydroperoxide, the fluorescence of which occurred transiently. The N(1) protonated species had been proposed as the emitter in the reaction with FMNH2, but the 1-deaza analog cannot be protonated at the corresponding position, thus excluding this possibility.

The chemistry of bioluminescence

The study of the mechanisms of bioluminescence is described from the standpoint of organic chemistry. An outline of the occurrence and function of the phenomenon is given, and the knowledge acquired by the organic chemist is set in this context.

Microassay with the NADH-induced light reaction, technique improved by means of purified enzymes from Achromobacter fischeri

Purification of a commercial preparation of Achromobacter fischeri was carried out by agarose-suspension electrophoresis and by molecular-sieve chromatography. Both the luciferase and an oxidoreductase, catalyzing reduction of FMN with NADH, were obtained in more than one form. Flavins, liable to interfere with the light production in analytical applications, were present in amounts worthy of consideration, but seem to be firmly bound to protein. The major quantity was found in the enzymatically inactive fractions. In free zone electrophoresis of the main luciferase component, the mobility of the zone containing enzyme activity was calculated to -4.0 X 10(-5) cm2 sec-1 V-1 at 12 degrees C. Fractions of the two enzymes were separated and mixed in different proportions to study how the intensity and time course of NADH-induced light emission can be modified. These experiments disclosed how reaction mixtures will have to be composed in appropriate photokinetic assays, using NADH as measurable product. A regenerating system based on the purified fractions is described. Instead of the light flash, following the consumption of NADH, the light is emitted on a well maintained level, permitting assays with a less elaborate equipment than the one required for the recording of fast reactions.

Reactions involved in bioluminescence systems of limpet (Latia neritoides) and luminous bacteria

Luminescence in Latia involves a specific flavoprotein enzyme ("luciferase"), which has a tightly bound flavin group constituting the light-emitter. The overall reaction includes oxidation of a specific substrate ("luciferin," an enol formate derivative of an aliphatic aldehyde), by 2 O(2) molecules, in the presence of a "purple protein" cofactor, yielding a ketone, HCOOH, CO(2), and light. In Achromobacter, a required aliphatic aldehyde, which is functionally equivalent to Latia luciferin, is oxidized to an acid containing the same hydrocarbon chain as the aldehyde; this reaction proceeds in the presence of bacterial luciferase and reduced flavin mononucleotide with a quantum yield of 0.17 + 0.1 photons per aldehyde molecule that is independent of aldehyde chain length from 9 to at least 14 carbons.