Bioluminescent Bacteria Research Articles

Identification of synergistic and antagonistic actions of environmental pollutants: Bisphenols A, S and F in the presence of DEP, DBP, BADGE and BADGE·2HCl in three component mixtures

Ecosystems are facing increased pressure due to the emission of many classes of emerging contaminants. However, very little is known about the interactions of these pollutants, such as bisphenols (BPs), plasticizers or pharmaceuticals. By employing bioluminescent bacteria (Microtox assay), we were able to define interactions between selected emerging pollutants (namely BPA, BPS, BPF, BADGE, BADGE·2HCl, DEP, DBP) in ternary mixtures, at environmentally relevant concentration levels (down to as low as 1.89, 1.42, 3.08, and 0.326 μM for, respectively, BPA, BPF, BPS and BADGE·2HCl). We provide the first systematic analysis of bisphenols and phthalates in three component mixtures. Using this system, we performed toxicity modelling with concentration addition (CA) and independent action (IA) approaches, followed by data interpretation using Model Deviation Ratio (MDR) evaluation. Interestingly, we mathematically and experimentally confirmed a novel synergy between BPA, BADGE and BADGE·2HCl. The synergy of BPA, BADGE and BADGE·2HCl is distinct, with both models suggesting these analytes have a similar mode of action (MOA). Moreover, we unexpectedly found a strong antagonistic impact with DEP, in mixtures containing BPA and BADGE analogues, which is confirmed with both mathematical models. Our study also shows that the impact of BPS and BPF in many mixtures is highly concentration dependent, justifying the necessity to perform mixture studies using wide concentration ranges. Overall, this study demonstrates that bioluminescent bacteria are a relevant model for detecting the synergistic and antagonist actions of environmental pollutants in mixtures, and highlights the importance of analyzing combinations of pollutants in higher order mixtures.

Imaging the oxygen wave with a single bioluminescent bacterium.

We developed a capability of a monolayer of bioluminescent (BL) bacteria for spatiotemporally visualizing the heterogeneous distribution and dynamic evolution of interfacial oxygen concentration, resulting in the discovery of spontaneous and stochastic oxygen waves at the interface between the substrate and an undisturbed, apparently still solution. Wild type bacteria, P. phosphoreum, spontaneously emit light during the native metabolism processes, i.e., bioluminescence. The emission intensity is sensitively regulated by oxygen concentration. By taking the electrolysis of water as a model, it was demonstrated that time-lapsed BL imaging of a bacterial monolayer allowed for visualizing the dynamic distribution of oxygen. The results were quantitatively understood with a physical model involving the diffusion equation and Michaelis–Menten equation. Unexpectedly, further study uncovered a spontaneous and stochastic oxygen wave in a standard well of a microtiter plate, which was subsequently attributed to the inevitable micro-convections induced by inhomogeneous evaporation and thermal fluctuation. Because of the wide application of microtiter plates, this study sheds new light to better understand the apparent heterogeneity in cell-culture and bio-assays.

Multiplexed Competition in a Synthetic Squid Light Organ Microbiome Using Barcode-Tagged Gene Deletions.

Beneficial symbioses between microbes and their eukaryotic hosts are ubiquitous and have widespread impacts on host health and development. The binary symbiosis between the bioluminescent bacterium Vibrio fischeri and its squid host Euprymna scolopes serves as a model system to study molecular mechanisms at the microbe-animal interface. To identify colonization factors in this system, our lab previously conducted a global transposon insertion sequencing (INSeq) screen and identified over 300 putative novel squid colonization factors in V. fischeri To pursue mechanistic studies on these candidate genes, we present an approach to quickly generate barcode-tagged gene deletions and perform high-throughput squid competition experiments with detection of the proportion of each strain in the mixture by barcode sequencing (BarSeq). Our deletion approach improves on previous techniques based on splicing by overlap extension PCR (SOE-PCR) and tfoX-based natural transformation by incorporating a randomized barcode that results in unique DNA sequences within each deletion scar. Amplicon sequencing of the pool of barcoded strains before and after colonization faithfully reports on known colonization factors and provides increased sensitivity over colony counting methods. BarSeq enables rapid and sensitive characterization of the molecular factors involved in establishing the Vibrio-squid symbiosis and provides a valuable tool to interrogate the molecular dialogue at microbe-animal host interfaces.IMPORTANCE Beneficial microbes play essential roles in the health and development of their hosts. However, the complexity of animal microbiomes and general genetic intractability of their symbionts have made it difficult to study the coevolved mechanisms for establishing and maintaining specificity at the microbe-animal host interface. Model symbioses are therefore invaluable for studying the mechanisms of beneficial microbe-host interactions. Here, we present a combined barcode-tagged deletion and BarSeq approach to interrogate the molecular dialogue that ensures specific and reproducible colonization of the Hawaiian bobtail squid by Vibrio fischeri The ability to precisely manipulate the bacterial genome, combined with multiplex colonization assays, will accelerate the use of this valuable model system for mechanistic studies of how environmental microbes-both beneficial and pathogenic-colonize specific animal hosts.

Solution structures of the Shewanella woodyi H-NOX protein in the presence and absence of soluble guanylyl cyclase stimulator IWP-051.

Heme-nitric oxide/oxygen binding (H-NOX) domains bind gaseous ligands for signal transduction in organisms spanning prokaryotic and eukaryotic kingdoms. In the bioluminescent marine bacterium Shewanella woodyi (Sw), H-NOX proteins regulate quorum sensing and biofilm formation. In higher animals, soluble guanylyl cyclase (sGC) binds nitric oxide with an H-NOX domain to induce cyclase activity and regulate vascular tone, wound healing and memory formation. sGC also binds stimulator compounds targeting cardiovascular disease. The molecular details of stimulator binding to sGC remain obscure but involve a binding pocket near an interface between H-NOX and coiled-coil domains. Here, we report the full NMR structure for CO-ligated Sw H-NOX in the presence and absence of stimulator compound IWP-051, and its backbone dynamics. Nonplanar heme geometry was retained using a semi-empirical quantum potential energy approach. Although IWP-051 binding is weak, a single binding conformation was found at the interface of the two H-NOX subdomains, near but not overlapping with sites identified in sGC. Binding leads to rotation of the subdomains and closure of the binding pocket. Backbone dynamics are similar across both domains except for two helix-connecting loops, which display increased dynamics that are further enhanced by compound binding. Structure-based sequence analyses indicate high sequence diversity in the binding pocket, but the pocket itself appears conserved among H-NOX proteins. The largest dynamical loop lies at the interface between Sw H-NOX and its binding partner as well as in the interface with the coiled coil in sGC, suggesting a critical role for the loop in signal transduction.

Influence of ultraviolet and gamma ray irradiation on luminescent bacteria and exploring their efficacy as biosensors.

Toxicity monitoring of harmful radiation is an indispensable issue in modern radioecology. As bioluminescent bacteria have the simplest structure to epitomize the biosphere, their bioluminescence can also act as an indicator of the conditions, therefore assay systems based on luminous bacteria can be used to monitor environmental radiotoxicity. The present investigation explored the measurement of bacterial luminescence, which can be easily computed. Bioluminescent bacterial strains were used to evaluate the effect of ultraviolet (UV) and gamma irradiation. A random amplified polymorphic DNA (RAPD) assay was carried out to observe alterations under exposure. Using a phylogenetic tree, a comparative study of the effect of UV and gamma rays was carried out. The isolated strains showed marked sensitivity towards radiation exposure present in the environment and therefore they could be used as potential biosensing elements for developing an on-site pollution monitoring biosensor.

In vitro Biofilm Formation by Bioluminescent Bacteria Isolated from the Marine Fish Gut.

The internal surface of the animal gastrointestinal tract is covered by microbial biofilms. They play an important role in the development and functioning of the host organism and protect it against pathogens. Microbial communities of gastrointestinal biofilms are less elucidated than luminal microbiota. Therefore, the studies of biofilm formation by gastrointestinal microorganisms are a topical issue. For the first time, we report the formation of a biofilm in vitro by the strains of bioluminescent bacteria isolated from the intestines of marine fish. These bacteria exhibit co-aggregation and tend to attach to solid surfaces. The attachment of cells is accompanied by appearance of the pili. Then, we observed the formation of microcolonies and the production of extracellular polymer substances (EPSs) connecting bacterial cells into an integrated system. The presence of acidic polysaccharides is shown in the EPS when using the ruthenium red staining. Acidic polysaccharides in this matrix is a biochemical evidence of microbial biofilms. On the fibers of the polymer matrix, these bacteria form the "mushroom body"-type structures. Matured biofilms exhibit a specific three-dimensional architecture with pores and channels formed by cells and EPS. We also demonstrated the formation of a biofilm by binary culture of the luminous enterobacterium Kosakonia cowanii and a Gram-positive Macrococcus sp. The data obtained help to understand the role of these bacteria in the intestines of fish. They lead to a new study in the field of investigation of the intestinal microbiome of fish.

Gut microbiome of the White Sea fish revealed by 16S rRNA metabarcoding

To date, it has been increasingly clear, that microbiota plays essential role in the host microorganism. Due to high phylogenetic diversity and wide distribution understanding of gut microbiota of fish is ambiguous. We elucidate previously undescribed diversity of bacteria in the White Sea fish posterior intestine based on 16S rRNA metabarcoding: shorthorn sculpin (Myoxocephalus scorpius), lumpfish (Cyclopterus lumpus) arctic flounder (Liopsetta glacialis), cod (Gadus morhua), and herring (Clupea pallasii). Proteobacteria were most abundant in all the samples. All datasets contained high number of reads corresponded to Psychrobacter, Halomonas, Pseudoalteromonas and Vibrio abundant in the White Sea water.Vast majority of bacterial reads corresponded to the Vibrionaceae (Aliivibrio, Vibrio, and Photobacterium). It is in accordance with our previous study focused on bioluminescent bacteria, where we isolated strains of these genera from the same fish intestine samples. The datasets of G. morhua and Cl. pallasii were enriched by reads of Shewanella (also isolated previously microbiologically due to luminescence of some its strains); the datasets of G. morhua and M. scorpius contained high number of Mycoplasma, which is in line with previous reports on the microbiome of marine fish gut from other geographical regions. Collectively, on the one hand, the study is a confirmation of known data on marine fish gut microbiome, on the other hand, it reveals some specific patterns of White Sea fish gut microbiota, e.g. presence of bacteria common for water from this region.

Biosensor Design for Detection of Mercury in Contaminated Soil Using Rhamnolipid Biosurfactant and Luminescent Bacteria

In this study, a biosensor is designed to remove mercury as a toxic metal contaminant from the soil. The rhamnolipid biosurfactant was used to extract the mercury sorbed to soil to the aqueous phase. An immobilized bioluminescent bacterium (Escherichia coli MC106) with pmerRBPmerlux plasmid is assisted for mercury detection. A significant decrease in luminescence level was observed in a biosensor system containing contaminated soil sample extract. The concentrations of extracting mercury are well correlated with the mercury toxicity data obtained from experimental biosensor systems according to the RBL value. The optimum aeration rate of 20 ml/min was obtained for the biosensor systems. The advantage of such a biosensor is the in situ quantification of mercury as a heavy metal contaminant in soils. Therefore, this system could be proposed as a good biosensor-based alternative for future detection of heavy toxic metals in soils.

A small RNA for a long-lasting relationship.

A recent study found that a small RNA released by the bioluminescent bacterium Vibrio fischeri modulates crucial host responses in the Hawaiian bobtailed squid Euprymna scolopes, revealing a new mode of communication in beneficial animal–bacterial symbioses.

Improved Aliivibrio fischeri based-toxicity assay: Graphene-oxide as a sensitivity booster with a mobile-phone application

Recently, many bioluminescence-based applications have arisen in several fields, such as biosensing, bioimaging, molecular biology, and human health diagnosis. Among all bioluminescent organisms, Aliivibrio fischeri (A. fischeri) is a bioluminescent bacterium used to carry out water toxicity assays since the late 1970s. Since then, several commercial A. fischeri-based products have been launched to the market, as these bacteria are considered as a gold standard for water toxicity assessment worldwide. However, the aforementioned commercial products rely on expensive equipment, requiring several reagents and working steps, as well as high-trained personnel to perform the assays and analyze the output data. For these reasons, in this work, we have developed for the first time a mobile-phone-based sensing platform for water toxicity assessment in just 5 min using two widespread pesticides as model analytes. To accomplish this, we have established new methodologies to enhance the bioluminescent signal of A. fischeri based on the bacterial culture in a solid media and/or using graphene oxide. Finally, we have addressed the biocompatibility of graphene oxide to A. fischeri, boosting the sensitivity of the toxicity assays and the bacterial growth of the lyophilized bacterial cultures for more user-friendly storage.

Changes in the aquatic ecotoxicological effects of Triton X-100 after UV photodegradation.

Various spray adjuvants including surfactants are widely used in agricultural pesticide formulations, and some of them may remain in soils and waters and impose more adverse effects than active pesticide ingredients on organisms. However, previous studies are more focused on the active pesticide ingredients than the adjuvants. Thus, this study investigates the changes in toxic effects of surfactants during photodegradation, which is one way of naturally degrading contaminants in natural waters. Triton X-100, a water-soluble non-ionic surfactant, was degraded using different types of UV radiation (UVA, UVB, and UVC), and the changes in the toxic effects were determined using bioluminescent bacteria and water flea. The Triton X-100 removals were negligible with UVA within 24 h, while its removal was 81% with UVB and almost complete with UVC. The NMR spectra indicated possible molecule rearrangement after photolysis. On the other hand, the toxic effects based on the mortality of Daphnia magna and the bioluminescence of Aliivibrio fischeri increased (i.e., lower EC50 values) after photodegradation, suggesting the generation of photoproducts that are likely to have higher toxic effects or higher bioavailability. Furthermore, the sensitivities of D. magna and A. fischeri for Triton X-100 and the photodegraded Triton X-100 were different. This study suggests that the changes in the chemical composition of the Triton X-100 containing water with photodegradation can lead to changes in the relative toxic effects on different aquatic organisms. Therefore, not only the management of parent compound (i.e., Triton X-100) but also the photoproducts generated from the parent compound need to be considered when managing water environment subject to photodegradation.

Enhanced detection of heavy metals using Vibrio alginolyticus PBR1 by optimizing luminescence medium through statistical modeling

The bioluminescent bacteria have been widely used for detecting toxic compounds present in aqueous systems where the light output declines due to the presence of toxic chemicals. In the present study, bioluminescent Vibrio alginolyticus PBR1 was used as a test organism. Optimum environmental conditions and amount of ingredients of luminescence medium were investigated to obtain maximum luminescence and growth by one-factor-at-a-time method and response surface methodology (RSM). The optimized environmental conditions such as incubation state, temperature and pH were found to be 120 rpm, 25 ℃ and 7.0 respectively. The RSM derived composition of optimized luminescence medium (g % w/v) was: NaCl, 1.22; yeast extract, 0.13 and peptone, 1.50. To measure the cytotoxic effect of heavy metals on PBR1, bioluminescence inhibition assay was carried out using optimized luminescence broth. The strain PBR1 showed highest sensitivity to chromium and lowest to arsenic with EC50 values of 9.06 mg L−1 and 34.43 mg L−1 respectively. The detection sensitivity was improved by using optimized luminescence medium since it comprised of less organic content that reduced the precipitation and complexation of heavy metals compared to other reported media with higher organic content. The study demonstrated that V. alginolyticus PBR1 can be used as a promising candidate for commercial toxicity testing kits for the detection and monitoring of toxic heavy metals.

Toxicity of binary mixtures of pesticides and pharmaceuticals toward Vibrio fischeri: Assessment by quantitative structure-activity relationships.

Pollutants in real aquatic systems commonly occur as chemical mixtures. Yet, the corresponding risk assessment is still mostly based on information on single-pollutant toxicity, accepting the assumption that pollutant mixtures exhibit additive toxicity effect which is often not the case. Therefore, it is still better to use the experimental approach. Unfortunately, experimental determination of toxicity for each mixture is practically unfeasible. In this study, quantitative structure-activity relationship (QSAR) models for the prediction of toxicity of binary mixtures towards bioluminescent bacteria Vibrio fischeri were developed at three toxicity levels (EC10, EC30 and EC50). For model development, experimentally determined toxicity values of 14 pollutants (pharmaceuticals and pesticides) were correlated with their structural features, applying multiple linear regression together with genetic algorithm. Statistical analysis, internal validation and external validation of the models were carried out. The toxicity is accurately predicted by all three models. EC30 and EC50 values are mostly influenced by geometrical distances between nitrogen and sulfur atoms. Furthermore, the simultaneous presence of oxygen and chlorine atoms in mixture can induce the increase in toxicity. At lower effect levels (EC10), nitrogen atom bonded to different groups has the highest impact on mixture toxicity. Thus, the analysis of the descriptors involved in the developed models can give insight into toxic mechanisms of the binary systems.

Smartphone-Based Whole-Cell Biosensor Platform Utilizing an Immobilization Approach on a Filter Membrane Disk for the Monitoring of Water Toxicants.

Bioluminescent bacteria whole-cell biosensors (WCBs) have been widely used in a range of sensing applications in environmental monitoring and medical diagnostics. However, most of them use planktonic bacteria cells that require complicated signal measurement processes and therefore limit the portability of the biosensor device. In this study, a simple and low-cost immobilization method was examined. The bioluminescent bioreporter bacteria was absorbed on a filter membrane disk. Further optimization of the immobilization process was conducted by comparing different surface materials (polyester and parafilm) or by adding glucose and ampicillin. The filter membrane disks with immobilized bacteria cells were stored at −20 °C for three weeks without a compromise in the stability of its biosensing functionality for water toxicants monitoring. Also, the bacterial immobilized disks were integrated with smartphones-based signal detection. Then, they were exposed to water samples with ethanol, chloroform, and H2O2, as common toxicants. The sensitivity of the smartphone-based WCB for the detection of ethanol, chloroform, and H2O2 was 1% (v/v), 0.02% (v/v), and 0.0006% (v/v), respectively. To conclude, this bacterial immobilization approach demonstrated higher sensitivity, portability, and improved storability than the planktonic counterpart. The developed smartphone-based WCB establishes a model for future applications in the detection of environmental water toxicants.

HbtR, a Heterofunctional Homolog of the Virulence Regulator TcpP, Facilitates the Transition between Symbiotic and Planktonic Lifestyles in Vibrio fischeri.

The bioluminescent bacterium Vibrio fischeri forms a mutually beneficial symbiosis with the Hawaiian bobtail squid, Euprymna scolopes, in which the bacteria, housed inside a specialized light organ, produce light used by the squid in its nocturnal activities. Upon hatching, E. scolopes juveniles acquire V. fischeri from the seawater through a complex process that requires, among other factors, chemotaxis by the bacteria along a gradient of N-acetylated sugars into the crypts of the light organ, the niche in which the bacteria reside. Once inside the light organ, V. fischeri transitions into a symbiotic, sessile state in which the quorum-signaling regulator LitR induces luminescence. In this work we show that expression of litR and luminescence are repressed by a homolog of the Vibrio cholerae virulence factor TcpP, which we have named HbtR. Further, we demonstrate that LitR represses genes involved in motility and chemotaxis into the light organ and activates genes required for exopolysaccharide production.IMPORTANCE TcpP homologs are widespread throughout the Vibrio genus; however, the only protein in this family described thus far is a V. cholerae virulence regulator. Here, we show that HbtR, the TcpP homolog in V. fischeri, has both a biological role and regulatory pathway completely unlike those in V. cholerae Through its repression of the quorum-signaling regulator LitR, HbtR affects the expression of genes important for colonization of the E. scolopes light organ. While LitR becomes activated within the crypts and upregulates luminescence and exopolysaccharide genes and downregulates chemotaxis and motility genes, it appears that HbtR, upon expulsion of V. fischeri cells into seawater, reverses this process to aid the switch from a symbiotic to a planktonic state. The possible importance of HbtR to the survival of V. fischeri outside its animal host may have broader implications for the ways in which bacteria transition between often vastly different environmental niches.

Escape of TLR5 Recognition by Leptospira spp.: A Rationale for Atypical Endoflagella.

Leptospira (L.) interrogans are invasive bacteria responsible for leptospirosis, a worldwide zoonosis. They possess two periplasmic endoflagellae that allow their motility. L. interrogans are stealth pathogens that escape the innate immune recognition of the NOD-like receptors NOD1/2, and the human Toll-like receptor (TLR)4, which senses peptidoglycan and lipopolysaccharide (LPS), respectively. TLR5 is another receptor of bacterial cell wall components, recognizing flagellin subunits. To study the contribution of TLR5 in the host defense against leptospires, we infected WT and TLR5 deficient mice with pathogenic L. interrogans and tracked the infection by in vivo live imaging of bioluminescent bacteria or by qPCR. We did not identify any protective or inflammatory role of murine TLR5 for controlling pathogenic Leptospira. Likewise, subsequent in vitro experiments showed that infections with different live strains of L. interrogans and L. biflexa did not trigger TLR5 signaling. However, unexpectedly, heat-killed bacteria stimulated human and bovine TLR5, but did not, or barely induced stimulation via murine TLR5. Abolition of TLR5 recognition required extensive boiling time of the bacteria or proteinase K treatment, showing an unusual high stability of the leptospiral flagellins. Interestingly, after using antimicrobial peptides to destabilize live leptospires, we detected TLR5 activity, suggesting that TLR5 could participate in the fight against leptospires in humans or cattle. Using different Leptospira strains with mutations in the flagellin proteins, we further showed that neither FlaA nor Fcp participated in the recognition by TLR5, suggesting a role for the FlaB. FlaB have structural homology to Salmonella FliC, and possess conserved residues important for TLR5 activation, as shown by in silico analyses. Accordingly, we found that leptospires regulate the expression of FlaB mRNA according to the growth phase in vitro, and that infection with L. interrogans in hamsters and in mice downregulated the expression of the FlaB, but not the FlaA subunits. Altogether, in contrast to different bacteria that modify their flagellin sequences to escape TLR5 recognition, our study suggests that the peculiar central localization and stability of the FlaB monomers in the periplasmic endoflagellae, associated with the downregulation of FlaB subunits in hosts, constitute an efficient strategy of leptospires to escape the TLR5 recognition and the induced immune response.

Water toxicity evaluations: Comparing genetically modified bioluminescent bacteria and CHO cells as biomonitoring tools

The use of water for drinking and agriculture requires knowledge of its toxicity. In this study, we compared the use of genetically modified bioluminescent (GMB) bacteria whose luminescence increases in the presence of toxicants and Chinese Hamster Ovary (CHO) cells for the characterization of the toxicity of water samples collected from a lake and streams, hydroponic and aquaponic farms, and a wastewater treatment plant. GMB bacteria were used to probe genotoxicity, cytotoxicity and reactive oxygen species-induced effects in the whole water samples. Unlike GMB bacteria, the use of CHO cells requires XAD resin-based pre-concentration of toxic material present in water samples for the subsequent cytotoxicity assay. In addition to the examination of the toxicity of the water from the different sources, the GMB bacteria were also used to test the XAD extracts diluted to the concentrations causing 50% growth inhibition of the CHO cells. The two biomonitoring tools provided different results when they were used to test the above-mentioned diluted XAD extracts. A pre-concentration procedure based on adsorption by XAD resins with subsequent elution was not sufficient to represent the material responsible for the toxicity of the whole water samples toward the GMB bacteria. Therefore, the use of XAD resin extracts may lead to major underestimates of the toxicity of water samples. Although the toxicity findings obtained using the GMB bacteria and CHO cells may not correlate with each another, the GMB bacteria assay did provide a mechanism-specific biomonitoring tool to probe the toxicity of water samples without a need for the pre-concentration step.

Reviews and syntheses: Bacterial bioluminescence – ecology and impact in the biological carbon pump

Abstract. Around 30 species of marine bacteria can emit light, a critical characteristic in the oceanic environment is mostly deprived of sunlight. In this article, we first review current knowledge on bioluminescent bacteria symbiosis in light organs. Then, focusing on gut-associated bacteria, we highlight that recent works, based on omics methods, confirm previous claims about the prominence of bioluminescent bacterial species in fish guts. Such host–symbiont relationships are relatively well-established and represent important knowledge in the bioluminescence field. However, the consequences of bioluminescent bacteria continuously released from light organs and through the digestive tracts to the seawater have been barely taken into account at the ecological and biogeochemical level. For too long neglected, we propose considering the role of bioluminescent bacteria and reconsidering the biological carbon pump, taking into account the bioluminescence effect (“bioluminescence shunt hypothesis”). Indeed, it has been shown that marine snow and fecal pellets are often luminous due to microbial colonization, which makes them a visual target. These luminous particles seem preferentially consumed by organisms of higher trophic levels in comparison to nonluminous ones. As a consequence, the sinking rate of consumed particles could be either increased (due to repackaging) or reduced (due to sloppy feeding or coprophagy/coprorhexy), which can imply a major impact on global biological carbon fluxes. Finally, we propose a strategy, at a worldwide scale, relying on recently developed instrumentation and methodological tools to quantify the impact of bioluminescent bacteria in the biological carbon pump.

Acute toxicity assessment of drinking water source with luminescent bacteria: Impact of environmental conditions and a case study in Luoma Lake, East China

Protecting the quality of lake watersheds by preventing and reducing their contamination is an effective approach to ensure the sustainability of the drinking water supply. In this study, acute toxicity assessment was conducted on the basis of acute bioluminescence inhibition assay using the marine bacterium Vibrio fischeri as the test organism and Luoma Lake drinking water source in East China as the research target. The suitable ranges of environmental factors, including pH value, organic matter, turbidity, hardness, and dissolved oxygen of water samples were evaluated for the toxicity testing of bioluminescent bacteria. The physicochemical characteristics of water samples at the selected 43 sites of Luoma Lake watershed were measured. Results showed that the variations in pH value (7.31–8.41), hardness (5–20 °d) and dissolved oxygen (4.44–11.03 mg/L) of Luoma Lake and its main inflow and outflow rivers had negligible impacts on the acute toxicity testing of V. fischeri. The luminescence inhibition rates ranged from −11.21% to 10.80% at the 43 sites. Pearson’s correlation analysis in the experiment revealed that temperature, pH value, hardness, and turbidity had no correlation with luminescence inhibition rate, whereas dissolved oxygen showed a weak statistically positive correlation with a Pearson correlation coefficient of 0.455 (p < 0.05).

Bioluminescence-Triggered Photoswitchable Bacterial Adhesions Enable Higher Sensitivity and Dual-Readout Bacterial Biosensors for Mercury.

We present a new concept for whole-cell biosensors that couples the response to Hg2+ with bioluminescence and bacterial aggregation. This allows us to use the bacterial aggregation to preconcentrate the bioluminescent bacteria at the substrate surface and increase the sensitivity of Hg2+ detection. This whole-cell biosensor combines a Hg2+-sensitive bioluminescence reporter and light-responsive bacterial cell-cell adhesions. We demonstrate that the blue luminescence in response to Hg2+ is able to photoactivate bacterial aggregation, which provides a second readout for Hg2+ detection. In return, the Hg2+-triggered bacterial aggregation leads to faster sedimentation and more efficient formation of biofilms. At low Hg2+ concentrations, the enrichment of the bacteria in biofilms leads to an up to 10-fold increase in the signal. The activation of photoswitchable proteins with biological light is a new concept in optogenetics, and the presented bacterial biosensor design is transferable to other bioluminescent reporters with particular interest for environmental monitoring.