Biochemistry and physiology of bioluminescent bacteria

Rational Design and Testing of Antibacterial Aloe Vera Hemostatic Hydrogel

Bleeding resulting from surgical procedures or trauma, including gunshot wounds, represents a life-threatening health issue. Therefore, the development of safe, effective, and convenient hemostatic agents is critical in securing the "golden time" to save patients' lives. Plant-derived compounds and plant extracts have been regarded as promising sources of hemostatic agents in previous studies, regulating hemostatic function with low toxicity and minimal side effects within the human body. Aloe vera-based hydrogels, which are characterized by flexible strength and high functionality, have emerged as a promising platform for wound applications due to their unique biocompatibility features. This study provides a comprehensive exploration of the utilization of thickening agents and natural agents such as xanthan gum, carrageenan, Carbomer, and alginate in applying aloe vera-based hydrogels as a hemostatic. Furthermore, it also tests the use of aloe vera-based hydrogels for therapeutic delivery at wound sites through the incorporation of various antimicrobial agents to extend the utility of the hydrogels beyond hemostasis. Our novel applied research utilizes aloe vera-based hydrogel as an antimicrobial hemostatic agent, providing valuable insights for a wide range of applications and highlighting its potential to enhance hemorrhage control in various emergency scenarios.

Mechanistic Insights into the Bacterial Luciferase-based Bioluminescence Resonance Energy Transfer Luminescence: The Role of Protein Complex Dimer

Bacterial bioluminescence holds significant potential in the realm of optical imaging due to the inherent advantages of bioluminescence and ease of operation. However, its practical utility is hindered by its low light intensity. The fusion of bacterial luciferase with a highly fluorescent protein has been demonstrated to significantly enhance autonomous luminescence. Nevertheless, the underlying mechanism behind this enhancement remains unclear, and there is a dearth of research investigating the mechanistic aspects of bioluminescence resonance energy transfer (BRET) luminescence, whether it occurs naturally or can be achieved through experimental means. In this study, we investigated the phenomenon of bacterial luciferase-based BRET luminescence employing a range of computational techniques, including structural modeling, molecular docking, molecular dynamics simulations, as well as combined quantum mechanics and molecular mechanics calculations. The theoretical findings suggest that the BRET luminescence occurs through resonance energy transfer between the excited bioluminophore and the ground chromophore within the protein complex dimer. The proposed mechanism of the protein complex dimer offers a microscopic understanding of the intriguing BRET phenomenon and has the potential to inspire further practical applications in the field of optical imaging.

Monitoring of the yogurt fermentation process based on a rapid bio-luminescent chiral pattern recognition of amino acids

A luminescent bacterial sensor array was established for the discrimination of multiple chiral amino acids and the monitoring of the yogurt fermentation process.

QM/MM Investigation of the Spectroscopic Properties of the Fluorophore of Bacterial Luciferase

We employ replica-exchange molecular dynamics (REMD) and a hybrid ab initio multiconfigurational quantum mechanics/molecular mechanics (QM/MM) approach to model the absorption and fluorescence properties of bacterial luciferin-luciferase. Specifically, we employ complete active space perturbation theory (CASPT2) and study the effect of active space, basis set, and IPEA shift on the computed energies. We discuss the effect of the protein environment on the fluorophore's excited-state potential energy surface and the role that the protein plays in enhancing the fluorescence quantum yield in bacterial bioluminescence.

NAD(P)H:FMN‑Oxidoreductase Functioning Under Macromolecular Crowding: In Vitro Modeling

The functioning of NAD(P)H:FMN‑oxidoreductase (Red) from Vibrio fischeri under conditions of macromolecular crowding (MMC) simulated in vitro by adding biopolymers (starch and gelatin) was studied. The dissociation rate constants and the activation energies of dissociation of Red to the subunits were calculated, and the process of denaturation of Red was analyzed. It is shown that the functioning of Red both under conditions of MMC and in diluted solutions is the same. This result refutes the common belief that the native conformation of enzymes in vivo is stabilized due to MMC as compared to the in vitro conditions.

Bioluminescence Microplate Assay of Cyanide with Escherichia coli Harboring a Plasmid Responsible for Cyanide-dependent Light Emission in Alginate Microenvironment

We describe the bioluminescence of a genetically engineered Escherichia coli harboring a recombined plasmid with a catalase gene promoter fused lux gene cluster, responsible for the generation of photons closely associated with respiratory inhibition, with the aim of applying it for cyanide sensing. This E. coli construct was favorably utilized for the microplate assay of cyanide by leveraging the microenvironment of the biocompatible alginate. The brightness of the bioluminescence, induced by cyanide stimulation of the respiration causative of the production of hydrogen peroxide, positively correlates with its concentration. Moreover, visualization of cyanide with a consumer digital camera, ranging in concentration from about 0.01 mg CN·L^-1 in the alginate sol to around 100 mg CN·L^-1 in its gel, was attained.

Multiple-species hormetic phenomena induced by indole: A case study on the toxicity of indole to bacteria, algae and human cells

Hormesis is a dose-response relationship phenomenon characterized by low-dose stimulation and high-dose inhibition. Although hormetic phenomena have been reported in broadly ranging biological areas, there is still no unified mechanism of hormesis. Investigating multiple-species hormesis of one compound and then exploring the possible mechanism may be an effective approach to clarify the reason for the occurrence of hormetic phenomena in a broad range of organisms. In this study, indole was selected as the test chemical due to the broad biological and hormetic effects of indole compounds. The results show that indole induces multiple-species hormetic phenomena in bacteria (Aliivibrio fischeri (A. fischeri), Escherichia coli and Bacillus subtilis), algae (Microcystis aeruginosa and Selenastrum capricornutum), and human cells (human skin fibroblasts and human cervical cancer cells). Through in-depth investigation of the time-dependent hormetic effects of indole, indole derivatives and indole's structural analogs on the bioluminescence of A. fischeri, indole ring has been identified as the potential key structure that causes indole to act on quorum sensing of A. fischeri to induce hormetic effects on the bioluminescence at lag, logarithmic, and stationary phases. Therefore, the occurrence of multiple-species hormetic phenomena is speculated to be derived from the action of indole on the cell-to-cell communication of organism cells. This paper can not only further confirm the generalizability of hormesis but also provide a reasonable explanation for hormesis, which will benefit the development of hormesis and the risk assessment of environmental pollutants.

Molecular Mechanisms of Bacterial Bioluminescence

Bioluminescence refers to the production of light by living organisms. Bioluminescent bacteria with a variety of bioluminescence emission characteristics have been identified in Vibrionaceae, Shewanellaceae and Enterobacteriaceae. Bioluminescent bacteria are mainly found in marine habitats and they are either free-floating, sessile or have specialized to live in symbiosis with other marine organisms. On the molecular level, bioluminescence is enabled by a cascade of chemical reactions catalyzed by enzymes encoded by the lux operon with the gene order luxCDABEG. The luxA and luxB genes encode the α- and β- subunits, respectively, of the enzyme luciferase producing the light emitting species. LuxC, luxD and luxE constitute the fatty acid reductase complex, responsible for the synthesis of the long-chain aldehyde substrate and luxG encodes a flavin reductase. In bacteria, the heterodimeric luciferase catalyzes the monooxygenation of long-chain aliphatic aldehydes to the corresponding acids utilizing reduced FMN and molecular oxygen. The energy released as a photon results from an excited state flavin-4a-hydroxide, emitting light centered around 490 nm. Advances in the mechanistic understanding of bacterial bioluminescence have been spurred by the structural characterization of protein encoded by the lux operon. However, the number of available crystal structures is limited to LuxAB (Vibrio harveyi), LuxD (Vibrio harveyi) and LuxF (Photobacterium leiognathi). Based on the crystal structure of LuxD and homology models of LuxC and LuxE, we provide a hypothetical model of the overall structure of the LuxCDE fatty acid reductase complex that is in line with biochemical observations.

Mechanistic explanation of time-dependent cross-phenomenon based on quorum sensing: A case study of the mixture of sulfonamide and quorum sensing inhibitor to bioluminescence of Aliivibrio fischeri

Cross-phenomenon in which the concentration-response curve (CRC) for a mixture crosses the CRC for the reference model has been identified in many studies, expressed as a heterogeneous pattern of joint toxic action. However, a mechanistic explanation of the cross-phenomenon has thus far been extremely insufficient. In this study, a time-dependent cross-phenomenon was observed, in which the cross-concentration range between the CRC for the mixture of sulfamethoxypyridazine (SMP) and (Z-)-4-Bromo-5-(bromomethylene)-2(5H)-furanone (C30) to the bioluminescence of Aliivibrio fischeri (A. fischeri) and the CRC for independent action model with 95% confidence bands varied from low-concentration to higher-concentration regions in a timely manner expressed the joint toxic action of the mixture changing with an increase of both concentration and time. Through investigating the time-dependent hormetic effects of SMP and C30 (by measuring the expression of protein mRNA, simulating the bioluminescent reaction and analyzing the toxic action), the underlying mechanism was as follows: SMP and C30 acted on the quorum sensing (QS) system of A. fischeri, which induced low-concentration stimulatory effects and high-concentration inhibitory effects; in the low-concentration region, the stimulatory effects of SMP and C30 made the mixture produce a synergistic stimulation on the bioluminescence; thus, the joint toxic action exhibited antagonism. In the high-concentration region, the inhibitory effects of SMP and C30 in the mixture caused a double block in the loop circuit of the QS system; thus, the joint toxic action exhibited synergism. With the increase of time, these stimulatory and inhibitory effects of SMP and C30 were changed by the variation of the QS system at different growth phases, resulting in the time-dependent cross-phenomenon. This study proposes an induced mechanism for time-dependent cross-phenomenon based on QS, which may provide new insight into the mechanistic investigation of time-dependent cross-phenomenon, benefitting the environmental risk assessment of mixtures.

Bioluminophore and Flavin Mononucleotide Fluorescence Quenching of Bacterial Bioluminescence-A Theoretical Study

Bacterial bioluminescence with continuous glow has been applied to the fields of environmental toxin monitoring, drug screening, and in vivo imaging. Nonetheless, the chemical form of the bacterial bioluminophore is still a bone of contention. Flavin mononucleotide (FMN), one of the light-emitting products, and 4a-hydroxy-5-hydro flavin mononucleotide (HFOH), an intermediate of the chemical reactions, have both been assumed candidates for the light emitter because they have similar molecular structures and fluorescence wavelengths. The latter is preferred in experiments and was assigned in our previous density functional study. HFOH displays weak fluorescence in solutions, but exhibits strong bioluminescence in the bacterial luciferase. FMN shows the opposite behavior; its fluorescence is quenched when it is bound to the luciferase. This is the first example of flavin fluorescence quenching observed in bioluminescent systems and is merely an observation, both the quenching mechanism and quencher are still unclear. Based on theoretical analysis of high-level quantum mechanics (QM), combined QM and molecular mechanics (QM/MM), and molecular dynamics (MD), this paper confirms that HFOH in its first singlet excited state is the bioluminophore of bacterial bioluminescence. More importantly, the computational results indicate that Tyr110 in the luciferase quenches the FMN fluorescence via an electron-transfer mechanism.

The joint effects of sulfonamides and quorum sensing inhibitors on Vibrio fischeri: Differences between the acute and chronic mixed toxicity mechanisms

Quorum sensing inhibitors (QSIs) are considered to be promising antibiotic alternatives and will be increasingly exposed to the environment together with antibiotics after their research and development process; it is therefore necessary to study the joint effects of QSIs and antibiotics. In this study, single and mixed toxicity of sulfonamide (SAs) and QSIs under acute and chronic conditions and their corresponding toxicity mechanisms were investigated. The results indicated that the acute joint effect was extremely complex, ranging from an antagonistic to synergistic response, while the chronic joint effect was primarily an antagonistic response. Using a molecular docking and regression model, we found that the acute joint effect could be determined by the hydrion's, ability to be oxidized, as well as the binding energy. The chronic joint effect was primarily an antagonistic response, which was due to the QSI competing against AHL for luxR generated by SAs, leading to negative effects of the QSI-luxR complexes on luxI. This phenomenon eventually weakened the stimulatory effect caused by SAs. Finally, the main differences between acute and chronic mixtures were analyzed: (1) The target protein was different between acute and chronic toxicity mixtures, and (2) effective concentration in acute and chronic toxicity mixtures was also different. These deep insights into mixed toxicity mechanisms will play an important role in the study of antibiotic resistance genes in response to antibiotic replacements.

Structural and biochemical properties of LuxF from Photobacterium leiognathi

The lux-operon of bioluminescent bacteria contains the genes coding for the enzymes required for light emission. Some species of Photobacteria feature an additional gene, luxF, which shows similarity to luxA and luxB, the genes encoding the heterodimeric luciferase. Isolated dimeric LuxF binds four molecules of an unusually derivatized flavin, i.e., 6-(3'-(R)-myristyl)-FMN (myrFMN). In the present study we have heterologously expressed LuxF in Escherichia coli BL21 in order to advance our understanding of the protein's binding properties and its role in photobacterial bioluminescence. Structure determination by X-ray crystallography confirmed that apo-LuxF possesses four preorganized binding sites, which are further optimized by adjusting the orientation of amino acid side chains. To investigate the binding properties of recombinant LuxF we have isolated myrFMN from Photobacterium leiognathi S1. We found that LuxF binds myrFMN tightly with a dissociation constant of 80±20 nM demonstrating that the purified apo-form of LuxF is fully competent in myrFMN binding. In contrast to LuxF, binding of myrFMN to luciferase is much weaker (Kd=4.0±0.4 μM) enabling LuxF to prevent inhibition of the enzyme by scavenging myrFMN. Moreover, we have used apo-LuxF to demonstrate that myrFMN occurs in all Photobacteria tested, irrespective of the presence of luxF indicating that LuxF is not required for myrFMN biosynthesis.

Multiple native flavin reductases in camphor-metabolizing Pseudomonas putida NCIMB 10007: functional interaction with two-component diketocamphane monooxygenase isoenzymes

Although they have been studied for nearly 50 years, the source of the FMNH2 needed for effective biooxidation by the 2,5- and 3,6-diketocamphane monooxygenase (DKCMO) isoenzymes induced by the growth of Pseudomonas putida NCIMB 10007 (ATCC 17453) on camphor remains incompletely characterized. Prior studies have focussed exclusively on enzymes present in cells harvested during late-exponential-phase growth despite considerable circumstantial evidence that the flavin reductase (FR) component of these multicomponent monooxygenases is subject to growth-phase-dependent variation. In this study, a number of alternative FMNH2-generating activities, including both conventional FRs and enzymes also able to serve as ferric reductases, were isolated from camphor-grown cells, and the relative level, and hence potential contribution, of these various proteins shown to vary considerably depending on the point of harvest of NCIMB 10007 within exponential-phase growth. While two constitutive monomeric ferric reductases (molecular masses 27.0 and 28.5 kDa) were found to be the major relevant sources of FMNH2 during the initial stages of growth on camphor-based media, a significant subsequent contribution throughout the mid- to late-exponential phases of growth was also made by the camphor-induced homodimeric 37.0 kDa FR Fred, recently reported to serve such a role exclusively. The possible involvement of camphor-induced putidaredoxin reductase (51.0 kDa) as a contributory activity was also investigated and considered. Studies with highly purified preparations of the isofunctional DKCMOs confirmed the potential of the various reductases to function effectively as sources of the requisite FMNH2 to both monooxygenases at different times throughout growth on camphor.

Application of enzyme bioluminescence in ecology

: This review examines the general principles of bioluminescent enzymatic toxicity bioassays and describes the applications of these methods and the implementation in commercial biosensors. Bioluminescent enzyme system technology (BEST) has been proposed in the bacterial coupled enzyme system, wherein NADH:FMN-oxidoreductase-luciferase substitutes for living organisms. BEST was introduced to facilitate and accelerate the development of cost-competitive enzymatic systems for use in biosensors for medical, environmental, and industrial applications. For widespread use of BEST, the multicomponent reagent "Enzymolum" has been developed, which contains the bacterial luciferase, NADH:FMN-oxidoreductase, and their substrates, co-immobilized in starch or gelatin gel. Enzymolum is the central part of Portable Laboratory for Toxicity Detection (PLTD), which consists of a biodetector module, a sampling module, a sample preparation module, and a reagent module. PLTD instantly signals chemical-biological hazards and allows us to detect a wide range of toxic substances. Enzymolum can be integrated as a biological module into the portable biodetector-biosensor originally constructed for personal use. Based on the example of Enzymolum and the algorithm for creating new enzyme biotests with tailored characteristics, a new approach was demonstrated in biotechnological design and construction. The examples of biotechnological design of various bioluminescent methods for ecological monitoring were provided. Possible applications of enzyme bioassays are seen in the examples for medical diagnostics, assessment of the effect of physical load on sportsmen, analysis of food additives, and in practical courses for higher educational institutions and schools. The advantages of enzymatic assays are their rapidity (the period of time required does not exceed 3-5 min), high sensitivity, simplicity and safety of procedure, and possibility of automation of ecological monitoring; the required luminometer is easily available.

Functional assembly of camphor converting two-component Baeyer-Villiger monooxygenases with a flavin reductase from E. coli

The major limitation in the synthetic application of two-component Baeyer-Villiger monooxygenases was addressed by identifying the 28-kDa flavin-reductase Fre from Escherichia coli as a suitable supplier of reduced FMN for these enzymes. Coexpression of Fre with either 2,5- or 3,6-diketocamphane monooxygenase from Pseudomonas putida NCIMB 10007 significantly enhanced the conversion of camphor and norcamphor serving as representative ketones. With purified enzymes, full conversion was achieved, while only slight amounts of product were formed in the absence of this flavin reductase. Fusion of the genes of Fre and DKCMOs into single open reading frame constructs resulted in unstable proteins exhibiting flavin reducing, but poor oxygenating activity, which led to overall decreased conversion of camphor.

Visualization of mitochondria in living cells with a genetically encoded yellow fluorescent protein originating from a yellow-emitting luminous bacterium

We have visualized redox and structural changes in the mitochondria of yeast Saccharomyces cerevisiae as a eukaryotic cell model using a genetically encoded yellow fluorescent protein (Y1-Yellow) and conventional fluorescence microscopy. Y1-Yellow originating from a yellow emitting luminous bacterium Aliivibrio sifiae Y1 was fused with a mitochondria-targeted sequence (mt-sequence). Y1-Yellow fluorescence arising only from the mitochondrial site and the color of yellow fluorescence could be easily differentiated from cellular autofluorescence and from that of conventional probes. Y1-Yellow expressing S. cerevisiae made the yellow fluorescence conspicuous at the mitochondrial site in response to reactive oxygen species (ROS) transiently derived in the wake of pretreatment with hydrogen peroxide. Based on our observation with Y1-Yellow fluorescence, we also showed that mitochondria rearrange to form a cluster structure surrounding chromosomal DNA via respiratory inhibition by cyanide, followed by the generation of ROS. In contrast, uptake of an uncoupler of oxidative phosphorylation is not responsible for mitochondrial rearrangement. These results indicate the utility of Y1-Yellow for visualization of mitochondrial vitality and morphology in living cells.

Activities, kinetics and emission spectra of bacterial luciferase-fluorescent protein fusion enzymes

A new approach to alter bacterial bioluminescence color was developed by fusing Vibrio harveyi luciferase with the coral Discosoma sp. fluorescent protein mOrange, a homolog of the Aequorea green fluorescent protein. Attachment of mOrange to the N- or C-terminus of luciferase α or β subunit, via a 5 or 10 residue linker, produced fully active fusion enzymes. However, only the fusion of mOrange to the N-terminus of luciferase α produced a new 560 nm emission. The differences in emission color by two such fusion enzymes from that of the wild-type luciferase (λ(max) 490 nm) were evident by eye or photographically with the aid of cut-off optical filters. In nonturnover reactions, light decay rates of fusion enzyme remained the same when monitored as the full-spectrum light or at 480 nm (from the luciferase emitter) or 570 nm (from mOrange). No 560 nm emission component was observed with a mixture of luciferase and free mOrange. These findings support that the 560 nm emission by the fusion enzyme was due to bioluminescence resonance energy transfer from luciferase to mOrange. We believe that the same approach could also alter the bacterial bioluminescence color by covalent attachment of other suitable fluorescent proteins or chromophores to luciferase.

Effects of magnesium sulfate on the luminescence of Vibrio fischeri under nutrient-starved conditions

In this study, we investigated the relationship between MgSO(4) and luminescence in Vibrio fischeri under nutrient-starved conditions. When V. fischeri was cultured in an artificial seawater medium, the luminescence intensity was low relative to that observed under normal growth conditions. It decreased during the initial 14 h, and then increased slightly at 24 h. This regulation of luminescence was not dependent on the quorum-sensing mechanism, because the cell densities had not reached a critical threshold concentration. Under MgSO(4)-starved conditions, luminescence was not fully induced at 14 h, and decreased at 24 h. In contrast, induction of luminescence occurred under MgSO(4)-supplemented conditions, but MgSO(4) alone was insufficient to induce luminescence, and required NaHCO(3) or KCl. These results suggest that the luminescence of V. fischeri is controlled by an exogenous sulfur source under nutrient-starved conditions. In addition, they indicate that the induction of sulfur-dependent luminescence is regulated by the NaHCO(3) or KCl concentration.

Bacterial bioluminescence, bioelectromagnetics and function

The biological functions of light emission in bacterial bioluminescence are not always obvious, especially if the bacteria are in a free-living mode. Experimental evidence suggests that light emission confers benefit to the bacteria themselves such as through photoreactivation and involves as much as 20% of cell energy metabolism. A theoretical model shows if the effect is mediated solely by light then cells should be luminescent at both high and low cell densities, therefore raising doubt over the photoreactivation hypothesis and suggesting that another cofactor is involved. It has been postulated that bioelectromagnetics may be involved in biological processes and be involved with coordinated activity in quorate cells. The cell densities associated with autoinduction coincide with a large change in coupling efficiency in the millimeter and submillimeter spectral region. In this paper it is suggested that one function of bioluminescence is as a pump, involving millimeter and submillimeter wave coupling that is of benefit to the quorum. This may be related to the observation that millimeter wave radiation exposure has been reported to induce changes in DNA conformation and possibly gene expression. Agents that change DNA conformation in bioluminescent bacteria can cause increases in light emission. This work may have implications for electromagnetic fields as quorum-quenching agents.

Characterization of In Vivo Reporter Systems for Gene Expression and Biosensor Applications Based on luxAB Luciferase Genes

Advances in genetic engineering methods have allowed the development of an increasing number of practical and scientific applications for bioluminescence with lux genes cloned from a variety of organisms. Bioluminescence derived from the shortened lux operon (luxAB genes) is a complex process, and applications seem to be proliferating in advance of an understanding of the underlying biochemical processes. In this report, we describe a two-phase kinetic behavior of the light emission which must be properly taken into account in any quantitative measurements of the bioluminescence signal. By using strains of Escherichia coli and Caulobacter crescentus, this behavior was characterized and interpreted in terms of the biochemistry underlying the bacterial luciferase mechanism. We show that the intensity profile of each of the two phases of the luminescence signal is responsive (and exhibits different sensitivities) to the concentration of added decanal and other components of the assay mix, as well as to the order of mixing and incubation times. This study illustrates the importance of appropriate protocol design, and specific recommendations for using the luxAB system as a molecular reporter are presented, along with versatile assay protocols that yield meaningful and reproducible signals.

Applications of microbial cell sensors

Since the first microbial cell sensor was studied by Karube et al. in 1977, many types of microbial cell sensors have been developed as analytical tools. The microbial cell sensor utilizes microbes as a sensing element and a transducer. The characteristics of microbial cell sensors as sensing devices are a complete contrast to those of enzyme sensors or immunosensors, which are highly specific for the substrates of interest, although the specificity of the microbial cell sensor has been improved by genetic modification of the microbe used as the sensing element. Microbial cell sensors have the advantages of tolerance to measuring conditions, a long lifetime, and good cost performance, and have the disadvantage of a long response time. In this review, applications of microbial cell sensors are summarized.

A rapid and simple evaluation system for gas toxicity using luminous bacteria entrapped by a polyion complex membrane

We have developed a rapid and simple gas toxicity evaluation system based on bioluminescence inhibition of a marine-derived wild luminous bacterium, Vibrio fischeri. The luminous bacteria were trapped using a thin polyion complex membrane in order to allow semi direct contact between the bacteria and toxic gases. Bioluminescence inhibition ratios of the present system to six reference gases, including benzene, trichloroethylene, acetone, NO(2), SO(2), and CO, were evaluated, and dose-response relationships were successfully obtained after 15 min of gas exposure, except for CO gas. The sensitivity to the five gases except for CO gas of the present system was 1-3 orders of magnitude higher than that in acute animal tests. The present system also allowed for the evaluation of overall toxicity of some environmental gases containing various chemicals. These results clearly demonstrated that the present system would be a valuable prototype for rapid and on-site acute toxicity detection of a gas mixture, such as environmental gases.

Steady-state bioluminescence of bacterial luciferase using electrochemical regeneration of flavin substrate and its application to inhibitory analysis

The model system for the biological reaction using a bacterial luciferase (BL) was developed and applied to the inhibitory analysis of the hydrophobic molecules for enzymatic reactions. The homemade flow electrochemical luminescence cell was embedded in the BL reaction system to regenerate the reduced form of the flavin mononucleotide, which is one of the substrates of the BL luminescence reaction, and to measure the luminescence intensity. The constant intensity of the continuous BL luminescence was observed using the continuous-flow BL reaction system. The proposed system was successfully applied to the inhibitory reaction of dodecaneamide on the BL luminescence reaction.

Observation of oscillation in bacterial luminescence

Oscillation in the bioluminescent intensity from a luminous bacteria suspension was observed. The time course of the luminescence intensity from a suspension containing luminous bacteria was measured. The oscillation mode changed with the liquid broth component. The optical density and dissolved oxygen (DO) concentration were measured simultaneously with the luminescence intensity, and a possibility was indicated that both diauxic growth and oxygen reaction-consumption resulted with oscillation.

Development of microbial sensors and their application

Many types of microbial sensors have been developed as analytical tools since the first microbial sensor was studied by Karube et al. in 1977. The microbial sensor consists of a transducer and microbe as a sensing element. The characteristics of the microbial sensors are a complete contrast to those of enzyme sensors or immunosensors, which are highly specific for the substrates of interest, although the specificity of the microbial sensor has been improved by genetic modification of the microbe used as the sensing element. Microbial sensors have the advantages of tolerance to measuring conditions, a long lifetime, and cost performance, and also have the disadvantage of a long response time. In this review, the long history of microbial sensor development is summarized.

A bioluminescent signal system: detection of chemical toxicants in water

Prototype technologies of a bioluminescent signal system (BSS) based on the luminous bacterium Photobacterium phosphoreum and three enzymatic bioluminescence systems have been proposed for detecting and signalling the presence of toxicants in water systems. A number of pesticides, mostly known as poisonous substances, similar in their structures and physicochemical properties, have been taken as model compounds of chemical agents. The effect of toxicants (organophosphates, derivatives of dithiocarbamide acid, and pyrethroid preparations) on the bioluminescence of the four systems has been analysed. EC(50) and EC(80) have been determined and compared to the maximum permissible concentration for each of the analysed substances. The triple-enzyme systems with ADH and trypsin have been shown to be more sensitive to organophosphorous compounds (0.13-11 mg/L), while the triple-enzyme system with trypsin is highly sensitive to lipotropic poison, a derivative of dithiocarbamine acid (0.03 mg/L). Sensitivities of the triple-enzyme systems to pyrethroid preparations are similar to those of luminous bacteria (0.9-5 mg/L). The results can be used to construct an alarm-test bioluminescence system for detecting chemical toxicants, based on intact bacteria or enzyme systems.

A novel lux operon in the cryptically bioluminescent fish pathogen Vibrio salmonicida is associated with virulence

The cold-water-fish pathogen Vibrio salmonicida expresses a functional bacterial luciferase but produces insufficient levels of its aliphatic-aldehyde substrate to be detectably luminous in culture. Our goals were to (i) better explain this cryptic bioluminescence phenotype through molecular characterization of the lux operon and (ii) test whether the bioluminescence gene cluster is associated with virulence. Cloning and sequencing of the V. salmonicida lux operon revealed that homologs of all of the genes required for luminescence are present: luxAB (luciferase) and luxCDE (aliphatic-aldehyde synthesis). The arrangement and sequence of these structural lux genes are conserved compared to those in related species of luminous bacteria. However, V. salmonicida strains have a novel arrangement and number of homologs of the luxR and luxI quorum-sensing regulatory genes. Reverse transcriptase PCR analysis suggests that this novel arrangement of quorum-sensing genes generates antisense transcripts that may be responsible for the reduced production of bioluminescence. In addition, infection with a strain in which the luxA gene was mutated resulted in a marked delay in mortality among Atlantic salmon relative to infection with the wild-type parent in single-strain challenge experiments. In mixed-strain competition between the luxA mutant and the wild type, the mutant was attenuated up to 50-fold. It remains unclear whether the attenuation results from a direct loss of luciferase or a polar disturbance elsewhere in the lux operon. Nevertheless, these findings document for the first time an association between a mutation in a structural lux gene and virulence, as well as provide a new molecular system to study Vibrio pathogenesis in a natural host.

Bioluminescence color modulation of Vibrio fischeri strain Y1 coupled with alterable levels of endogenous yellow fluorescent protein and its fluorescence imaging

Bioluminescence (BL) (lambda(max) approximately 535 nm) of Vibrio fischeri strain Y1 has been previously characterized in terms of the fluctuation in intracellular levels of yellow fluorescent protein (YFP). In this study fluorescence microscopic analysis has revealed that yellow fluorescence, as well as blue fluorescence attributable to a luciferase intermediate, is localized to the periphery of V. fischeri Y1 cells. This finding indicates that both YFP and the luciferase are present in the vicinity of the cell membrane. By using cyanide to enhance yellow BL, it has been shown that BL modulation is coupled with the fluctuations in the intracellular levels of YFP and the primary emitter. On the basis of the BL characterization, combined with results of a sedimentation experiment, it has been shown that larger cells produce a relatively stronger yellow BL. Two-dimensional gel electrophoresis of cell-protein extracts has shown that the YFP level is more alterable than the luciferase level. It is postulated that the yellow BL modulation takes place in connection with cell growth.

A new short-term toxicity assay using Aspergillus awamori with recombinant aequorin gene

Background

Most currently available short-term toxicity assays are based on bacterial cells. Therefore there is a need for novel eukaryotic microbial bioassays that will be relevant to higher eukaryotes such as animals and plants. Ca²⁺ is a universal intracellular signalling molecule found in all organisms from prokaryotes to highly specialized animal cells. In fungi calcium has been demonstrated to be involved in control of many important processes. The recombinant aequorin gene from the jellyfish Aequorea victoria responsible for the expression of the Ca²⁺-sensitive aequorin photoprotein has been cloned in the filamentous fungus Aspergillus awamori. This has allowed real life monitoring of [Ca²⁺]_c changes in living fungal cells. When subjected to different physico-chemical stimuli fungal cells respond by transiently changing the concentration of free Ca²⁺ in the cytosol ([Ca²⁺]_c) and the pattern of these changes (Ca²⁺ signature) is specific to each particular stimulus. Therefore it was interesting to investigate whether different environmental toxicants would be able to affect the pattern of [Ca²⁺]_c changes in a reproducible and dose dependant manner.

Results

Toxicity bioassay has been developed to monitor changes [Ca²⁺]_c of the recombinant fungus in the presence of toxicants representing heavy metals – Cr⁶⁺ and Zn²⁺ and a phenolic polar narcotic -3,5-DCP. The fungus responds to toxicants by a decrease in the amplitude of [Ca²⁺]_c response to 5 mM external CaCl₂ and an increase in Ca²⁺ final resting levels and recovery time.

Conclusion

A novel toxicity bioassay utilizing eukaryotic cells has been developed based on filamentous fungi transformed with the recombinant aequorin gene. A range of parameters characterising changes in [Ca²⁺]_c has been identified, e.g. Amplitude, Length of Transient, Final Resting Level and Recovery Time. These parameters can be used to determine the toxicity of a range of chemicals to eukaryotic cells in a 96-well microtitre plate method.

Biosynthesis of the Unique Amino Acid Side Chain of Butirosin: Possible Protective-Group Chemistry in an Acyl Carrier Protein-Mediated Pathway

Butirosins A and B are naturally occurring aminoglycoside antibiotics that have a (2S)-4-amino-2-hydroxybutyrate (AHBA) side chain. Semisynthetic addition of AHBA to clinically valuable aminoglycoside antibiotics has been shown both to improve their pharmacological properties and to prevent their deactivation by a number of aminoglycoside-modifying enzymes involved in bacterial resistance. We report here that the biosynthesis of AHBA from L-glutamate, encoded within a previously identified butirosin biosynthetic gene cluster, proceeds via intermediates tethered to a specific acyl carrier protein (ACP). Five components of the pathway have been purified and characterized, including the ACP (BtrI), an ATP-dependent ligase (BtrJ), a pyridoxal phosphate-dependent decarboxylase (BtrK), and a two-component flavin-dependent monooxygenase system (BtrO and the previously unreported BtrV). The proposed biosynthetic pathway includes a gamma-glutamylation of an ACP-derived gamma-aminobutyrate intermediate, possibly a rare example of protective group chemistry in biosynthesis.

In situ measurement of bioluminescence and fluorescence in an integrated microbioreactor

Reporter strains of bacteria that emit light or a fluorescent marker in response to specific conditions in their environment are having a significant impact in many areas of biology, including toxicity assays for environmental pollutants, chemical detection, and gene expression profiling. We have demonstrated methods for in situ measurements of bioluminescence and fluorescence from bacterial cultures grown in 50 microL instrumented microbioreactors. Results from microbioreactors were compared to results obtained from conventional 500 mL batch bioreactors and shake flasks. Experiments were conducted with reporter strains of Escherichia coli in which luxCDABE or gfp was fused to a promoter that was either expressed constitutively, or that responded to oxygen limitation. With these reporter strains, we have demonstrated the ability to obtain information on growth conditions within the microbioreactor. We have also shown that the large aspect ratio of the microbioreactor provides a unique advantage over measurements in larger bioreactors by reducing the inner filter effect in on-line measurements and eliminating the need for error-prone off-line dilutions. In addition, continuous on-line monitoring of genes in real-time, when expanded to include entire reporter libraries, could potentially provide a true dynamic picture of cellular gene expression from which the kinetics of gene expression can be untangled and elucidated.

Bright fluorescence of a novel protein from Vibrio vulnificus depends on NADPH and the expression of this protein is regulated by a LysR-type regulatory gene

A blue fluorescent protein, BfgV, belonging to the short-chain dehydrogenase/reductase superfamily, was found in a non-bioluminescent pathogen Vibrio vulnificus CKM-1. This protein has fluorescence spectra with two excitation peaks at 283 and 352 nm, and one emission peak at 456 nm. BfgV fluoresces through effectively augmenting the intrinsic fluorescence of NADPH bound to it. Escherichia coli transformants expressing this protein can emit eye-detectable fluorescence. A LysR-type transcriptional regulator gene bfgR was found at the vicinal upstream region of bfgV in CKM-1 genome. The clues that products of bfgR can specifically bind to bfgR-bfgV intergenic promoter region and the deletion of bfgR significantly decreases the expression of bfgV reveal bfgR is a repressor gene of bfgV in V. vulnificus CKM-1.

Chemical-chemical interaction between cyanogenic toxicants and aldehydes: a mechanism-based QSAR approach to assess toxicological joint effects

A QSAR approach was proposed to assess toxicological joint effects based on the mechanism of chemical-chemical interactions between cyanogenic toxicants and aldehydes. It has been observed that the chemical-chemical interaction between cyanogenic toxicants and aldehydes resulted in the formation of carbanion intermediates, and therefore this interaction led to different toxicological joint effects between cyanogenic toxicants and aldehydes. Analysis of this chemical-chemical interaction showed that the formation of carbanion intermediate highly depended on the charge of the carbon atom in the -CHO of aldehydes and this of the carbon atom (C*) in the carbochain of cyanogenic toxicant. By using the Hammett Constant (sigma(p)) to measure the charge of carbon atom in the -CHO of aldehydes, a mechanism-based QSAR approach (M = 0.316 - 4.386sigma(p) with r2 = 0.933, SE = 0.082, F = 55.389, p = 0.002, M = sum of toxic units) was proposed to assess the toxicological joint effects between alpha-hydroxy-isobutyronitrile and individual aliphatic aldehydes. Another one (M = 0.978 - 0.720sigma(p) with r2 = 0.852, SE = 0.152, F = 40.148, p = 0.0001) was also proposed to assess the toxicological joint effects between alpha-hydroxy-isobutyronitrile and individual aromatic aldehydes. Lastly, by using the charge of carbon atom (C*) in the carbochain of cyanogenic toxicant, a mechanism-based QSAR model (M = -0.161 - 7.721C* with r2 = 0.847, SE = 0.227, F = 27.657, p = 0.003) was derived to assess toxicological joint effects between p-nitrobenzaldehyde and cyanogenic toxicants.