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Successful practical implementation of bioelectrochemical systems (BES) requires developing affordable electrode structures that promote efficient electrical communication with microbes. Recent efforts have centered on immobilizing bacteria with organic semiconducting polymers on electrodes via electrochemical methods. This approach creates a fixed biocomposite that takes advantage of the increased electrode's electroactive surface area (EASA). Here, it is demonstrated that a biocomposite comprising the water-soluble conjugated polyelectrolyte CPE-K and electrogenic Shewanella oneidensis MR-1 can self-assemble with carbon paper electrodes, thereby increasing its biocurrent extraction by ≈6-fold over control biofilms. A ≈1.5-fold increment in biocurrent extraction is obtained for the biocomposite on carbon paper relative to the biocurrent extracted from gold-coated counterparts. Electrochemical characterization revealed that the biocomposite stabilized with the carbon paper more quickly than atop flat gold electrodes. Cross-sectional images show that the biocomposite infiltrates inhomogeneously into the porous carbon structure. Despite an incomplete penetration, the biocomposite can take advantage of the large EASA of the electrode via long-range electron transport. These results show that previous success on gold electrode platforms can be improved when using more commercially viable and easily manipulated electrode materials.
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Fontes de Energia Bioelétrica , Fontes de Energia Bioelétrica/microbiologia , Biofilmes , Carbono/química , Eletrodos , Transporte de Elétrons , Ouro/química , PolieletrólitosRESUMO
Biobutanol production by fermentation is potentially a sustainable alternative to butanol production from fossil fuels. However, the toxicity of butanol to fermentative bacteria, resulting largely from cell membrane fluidization, limits production titers and is a major factor limiting the uptake of the technology. Here, studies were undertaken, in vitro and in silico, on the butanol effects on a representative bacterial (i.e. Escherichia coli) inner cell membrane. A critical butanol : lipid ratio for stability of 2 : 1 was observed, computationally, consistent with complete interdigitation. However, at this ratio the bilayer was â¼20% thicker than for full interdigitation. Furthermore, butanol intercalation induced acyl chain bending and increased disorder, measured as a 27% lateral diffusivity increase experimentally in a supported lipid bilayer. There was also a monophasic Tm reduction in butanol-treated large unilamellar vesicles. Both behaviours are inconsistent with an interdigitated gel. Butanol thus causes only partial interdigitation at physiological temperatures, due to butanol accumulating at the phospholipid headgroups. Acyl tail disordering (i.e. splaying and bending) fills the subsequent voids. Finally, butanol short-circuits the bilayer and creates a coupled system where interdigitated and splayed phospholipids coexist. These findings will inform the design of strategies targeting bilayer stability for increasing biobutanol production titers.
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1-Butanol/química , Membrana Celular/química , Bicamadas Lipídicas/química , Escherichia coli/química , Simulação de Dinâmica Molecular , Fosfatidiletanolaminas/química , Fosfatidilgliceróis/química , Temperatura de Transição , Lipossomas Unilamelares/químicaRESUMO
Waterborne infections are responsible for health problems worldwide and their prompt and sensitive detection in recreational and potable water is of great importance. Bacterial identification and enumeration in water samples ensures water is safe for its intended use. Culture-based methods can be time consuming and are usually performed offsite. There is a need to for automated and distributed at-source detectors for water quality monitoring. Herein we demonstrate a microvolume Escherichia coli (E. coli) detector based on a screen printed electrode (SPE) bioelectroanalytical system and explore to what extent performance can be improved by coupling it with a filtration device. To confidently benchmark detector performance, we applied a statistical assessment method to target optimal detection of a simulated concentrated sample. Our aim was to arrive at a holistic understanding of device performance and to demonstrate system improvements based on these insights. The best achievable detection time for a simulated 1 CFU mL-1 sample was 4.3 (±0.6) h assuming no loss of performance in the filtration step. The real filtered samples fell short of this, extending detection time to 16-18 h. The loss in performance is likely to arise from stress imposed by the filtration step which inhibited microbial growth rates.
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Técnicas Eletroquímicas/instrumentação , Escherichia coli/isolamento & purificação , Eletrodos , Fatores de TempoRESUMO
Turning wastewater directly into electricity is alluring, widespread use of microbial fuel cells (MFCs) to achieve this at industrial scale appears increasingly unlikely despite intense research efforts lasting over a decade. Such endeavors have not been futile, however, and game-changing discoveries have resulted from these well-intentioned, scientifically rigorous but ultimately frustrated attempts to resolve the Waste-Energy dichotomy. The appeal of MFCs is largely of conceptual elegance rather than financial competitiveness, based on the green ideal that bacteria can be turned into cost effective bio-batteries. This notion is founded on the solid principles of extracellular electron transfer (EET), where microbes use electrodes interchangeably with other electron acceptors to generate current as a direct proxy for microbial metabolism. We contend that a nuanced understanding of EET has been restricted by focusing on device performance when in fact this information could be more beneficially channeled into addressing analytical questions pertaining to the presence and activity of microorganisms across systems of environmental and medical import, i.e. bioelectroanalytics. We discuss here relevant literature detailing bioelectrochemical systems and contrast energy-centric conclusions with observations geared towards bioelectroanalytics. We explore the expanding possibilities of bioelectroanalytics enabled by advances in genetic techniques and rooted in the concept that microbial interactions with an electrode extend to more than just cells seeking alternative electron acceptors. Our intention is to highlight alternative directions in the field and encourage researchers to harness bioelectroanalytics to address wider societal problems, in addition to addressing climate change.
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Fontes de Energia Bioelétrica/microbiologia , Transporte de Elétrons/fisiologia , Águas Residuárias/microbiologia , Bactérias/metabolismo , EletrodosRESUMO
Membrane-intercalating conjugated oligoelectrolytes (COEs) are emerging as potential alternatives to conventional, yet increasingly ineffective, antibiotics. Three readily accessible COEs, belonging to an unreported series containing a stilbene core, namely D4, D6, and D8, were designed and synthesized so that the hydrophobicity increases with increasing side-chain length. Decreased aqueous solubility correlates with increased uptake by E.â coli. The minimum inhibitory concentration (MIC) of D8 is 4â µg mL-1 against both E.â coli and E.â faecalis, with an effective uptake of 72 %. In contrast, the MIC value of the shortest COE, D4, is 128â µg mL-1 owing to the low cellular uptake of 3 %. These findings demonstrate the application of rational design to generate efficacious antimicrobial COEs that have potential as low-cost antimicrobial agents.
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Anti-Infecciosos/química , Desenho de Fármacos , Polieletrólitos/química , Anti-Infecciosos/metabolismo , Anti-Infecciosos/farmacologia , Varredura Diferencial de Calorimetria , Enterococcus faecalis/efeitos dos fármacos , Escherichia coli/efeitos dos fármacos , Bicamadas Lipídicas/química , Bicamadas Lipídicas/metabolismo , Testes de Sensibilidade Microbiana , Polieletrólitos/síntese química , Polieletrólitos/farmacologia , Estilbenos/químicaRESUMO
The modification of microbial membranes to achieve biotechnological strain improvement with exogenous small molecules, such as oligopolyphenylenevinylene-conjugated oligoelectrolyte (OPV-COE) membrane insertion molecules (MIMs), is an emerging biotechnological field. Little is known about the interactions of OPV-COEs with their target, the bacterial envelope. We studied the toxicity of three previously reported OPV-COEs with a selection of Gram-negative and Gram-positive organisms and demonstrated that Gram-positive bacteria are more sensitive to OPV-COEs than Gram-negative bacteria. Transmission electron microscopy demonstrated that these MIMs disrupt microbial membranes and that this occurred to a much greater degree in Gram-positive organisms. We used a number of mutants to probe the nature of MIM interactions with the microbial envelope but were unable to align the membrane perturbation effects of these compounds to previously reported membrane disruption mechanisms of, for example, cationic antimicrobial peptides. Instead, the data support the notion that OPV-COEs disrupt microbial membranes through a suspected interaction with diphosphatidylglycerol (DPG), a major component of Gram-positive membranes. The integrity of model membranes containing elevated amounts of DPG was disrupted to a greater extent by MIMs than those prepared from Escherichia coli total lipid extracts alone.
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Membrana Celular/efeitos dos fármacos , Bactérias Gram-Positivas/efeitos dos fármacos , Polivinil/metabolismo , Polivinil/toxicidade , Bactérias Gram-Negativas/citologia , Bactérias Gram-Negativas/efeitos dos fármacos , Bactérias Gram-Positivas/citologia , Microscopia Eletrônica de TransmissãoRESUMO
Certain conjugated oligoelectrolytes (COEs) modify biological function by improving charge transfer across biological membranes as demonstrated by their ability to boost performance in bioelectrochemical systems. Molecular level understanding of the nature of the COE/membrane interactions is lacking. Thus, we investigated cell membrane perturbation by three COEs differing in the number of aromatic rings and presence of a fluorine substitution. Molecular dynamic simulations showed that membrane deformation by all COEs resulted from membrane thinning as the lipid phosphate heads were drawn toward the center of the bilayer layer by positively charged COE side chains. The four-ringed COE, which most closely resembled the lipid bilayer in length, deformed the membrane the least and was least disruptive, as supported by toxicity testing (minimum inhibitory concentration (MIC) = 64 µmol L(-1)) and atomic force microscopy (AFM). Extensive membrane thinning was observed from three-ringed COEs, reducing membrane thickness to <3.0 nm in regions where the COEs were located. Severe localized membrane pitting was observed when the central aromatic ring was unfluorinated, as evident from AFM and simulations. Fluorinating the central aromatic ring delocalized thinning but induced greater membrane disorder, indicated by changes in deuterium order parameter of the acyl chains. The fluorinated three-ringed compound was less toxic (MIC 4 µmol L(-1)) than the nonfluorinated three-aromatic-ringed COE (MIC 2 µmol L(-1)); thus, hydrophobic polar interactions resulting from fluorine substitution of OPV COEs dissipate membrane perturbations. Correlating specific structural features with cell membrane perturbation is an important step toward designing non-antimicrobial membrane insertion molecules.
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Membrana Celular/química , Simulação de Dinâmica Molecular , Fosfatidiletanolaminas/química , Fosfatidilgliceróis/química , Eletrólitos/química , Transporte de Elétrons , Escherichia coli/química , Escherichia coli/citologia , Bicamadas Lipídicas/química , Estrutura MolecularRESUMO
It is important to tailor biotic-abiotic interfaces in order to maximize the utility of bioelectronic devices such as microbial fuel cells (MFCs), electrochemical sensors and bioelectrosynthetic systems. The efficiency of electron-equivalent extraction (or injection) across such biotic-abiotic interfaces is dependent on the choice of the microbe and the conductive electrode material. In this contribution, we show that spontaneous intercalation of a conjugated oligoelectrolyte, namely 4,4'-bis(4'-(N,N-bis(6''-(N,N,N-trimethylammonium)hexyl)amino)-styryl)stilbene tetraiodide (DSSN+), into the membranes of Escherichia coli leads to an increase in current generation in MFCs containing carbon-based electrodes. A combination of scanning electron microscopy (SEM) and confocal microscopy was employed to confirm the incorporation of DSSN+ into the cell membrane and biofilm formation atop carbon felt electrodes. Current collection was enhanced by more than 300% with addition of this conjugated oligoelectrolyte. The effect of DSSN+ concentration on electrical output was also investigated. Higher concentrations, up to 25 µM, lead to an overall increase in the number of charge equivalents transferred to the charge-collecting electrode, providing evidence in support of the central role of the synthetic system in improving device performance.
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Carbono/química , Eletrólitos/química , Escherichia coli/metabolismo , Compostos de Amônio Quaternário/química , Estilbenos/química , Fontes de Energia Bioelétrica , Membrana Celular/química , Membrana Celular/metabolismo , Eletricidade , Eletrodos , Microscopia Eletrônica de Varredura , Compostos de Amônio Quaternário/síntese química , Estilbenos/síntese químicaRESUMO
BACKGROUND: Alcohol is a good and environment-friendly fuel that can be microbially produced, capable of eliminating many of the limitations of the present-day fossil fuels. However, the inherent toxic nature of alcohols to the microbial cells leads to end-product inhibition that limits large-scale alcohol production by fermentation. Fundamental knowledge about the stress responses of microorganisms to alcohols would greatly facilitate to improve the microbial alcohol tolerance. The current study elucidates and compares the changes in the membrane proteome of Escherichia coli in response to a range of alcohols. RESULTS: Although alcohol toxicity increased exponentially with alcohol chain length (2-6 carbon), similar stress responses were observed in the inner and outer membrane proteome of E. coli in the presence of 2-, 4- and 6-carbon alcohols at the MIC50. This pertains to: (1) increased levels of inner membrane transporters for uptake of energy-producing metabolites, (2) reduced levels of non-essential proteins, associated with anaerobic, carbon starvation and osmotic stress, for energy conservation, (3) increased levels of murein degrading enzymes (MltA, EmtA, MliC and DigH) promoting cell elongation and 4) reduced levels of most outer membrane ß-barrel proteins (LptD, FadL, LamB, TolC and BamA). Major outer membrane ß-barrel protein OmpC, which is known to contribute to ethanol tolerance and membrane integrity, was notably reduced by alcohol stress. While LPS is important for OmpC trimerisation, LPS release by EDTA did not lower OmpC levels. This suggests that LPS release, which is reported under alcohol stress, does not contribute to the reduced levels of OmpC in the presence of alcohol. CONCLUSIONS: Since alcohol primarily targets the integrity of the membrane, maintenance of outer membrane OmpC levels in the presence of alcohol might help in the survival of E. coli to higher alcohol concentrations. The study provides important information about the membrane protein responses of E. coli to a range of alcohols, which can be used to develop targeted strategies for increased microbial alcohol tolerance and hence bioalcohol production.
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We report the complete genome sequence of Methylomonas sp. UP202 isolated from an urban waterway sediment in Singapore. The genome contains genes involved in methane, methanol, formaldehyde, and formate oxidation. It also contains genes utilizing various nitrogen sources such as nitrogen, nitrate, nitrite, urea, and ammonium.
RESUMO
In the case of many bacteria, such as Escherichia coli, the composition of lipid molecules, termed the lipidome, temporally adapts to different environmental conditions and thus modifies membrane properties to permit growth and survival. Details of the relationship between the environment and lipidome composition are lacking, particularly for growing cultures under either favourable or under stress conditions. Here, we highlight compositional lipidome changes by describing the dynamics of molecular species throughout culture-growth phases. We show a steady cyclopropanation of fatty acyl chains, which acts as a driver for lipid diversity. There is a bias for the cyclopropanation of shorter fatty acyl chains (FA 16:1) over longer ones (FA 18:1), which likely reflects a thermodynamic phenomenon. Additionally, we observe a nearly two-fold increase in saturated fatty acyl chains in response to the presence of ampicillin and chloramphenicol, with consequences for membrane fluidity and elasticity, and ultimately bacterial stress tolerance. Our study provides the detailed quantitative lipidome composition of three E. coli strains across culture-growth phases and at the level of the fatty acyl chains and provides a general reference for phospholipid composition changes in response to perturbations. Thus, lipidome diversity is largely transient and the consequence of lipid synthesis and cyclopropanation.
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The outer membrane (OM) is the first defence for Gram-negative bacteria against their environments making it important in strain improvement for sustainable biobutanol production. While modifying the OM structure using chemical additives could enhance microbial viability, there are currently no model systems that accurately describe OM responses to butanol. Here, we experimentally determined that reducing the lipopolysaccharide (LPS) core length and charge increased Escherichia coli sensitivity to butanol. In silico models were built to describe how OM structure contributes to its ability to withstand butanol under conditions of exposure and production. Consistent with experiments, resistance to ingress of butanol into OMs correlates with both core length and charge, where a lower charge density is more conducive to butanol assimilation. The core length and branching correlate with the lateral spacing of the lipids, suggestive of a role of them in maintaining OM fluidity. In contrast to systems with short-length LPS cores, butanol intercalation into OMs with longer LPS cores increases membrane order and rigidity, which might be due to their more porous internal structure. These findings will assist the development of more butanol-tolerant biobutanol-producing bacteria, where thicker, more compact and less polar LPS-core surfaces reinforce the integrity of OMs and further improve resilience in extreme environments.
Assuntos
Butanóis/química , Membrana Celular/efeitos dos fármacos , Lipopolissacarídeos/química , Butanóis/farmacologia , Membrana Celular/química , Escherichia coli/efeitos dos fármacos , Fluidez de Membrana , Simulação de Dinâmica MolecularRESUMO
Conjugated oligoelectrolytes (COEs) are emerging antimicrobials with broad spectrum activity against Gram positive and Gram negative bacteria as well as fungi. Our previous in vitro evolution studies using Enterococcus faecalis grown in the presence of two related COEs (COE1-3C and COE1-3Py) led to the emergence of mutants (changes in liaF and liaR) with a moderate 4- to16-fold increased resistance to COEs. The contribution of liaF and liaR mutations to COE resistance was confirmed by complementation of the mutants, which restored sensitivity to COEs. To better understand the cellular target of COEs, and the mechanism of resistance to COEs, transcriptional changes associated with resistance in the evolved mutants were investigated in this study. The differentially transcribed genes encoded membrane transporters, in addition to proteins associated with cell envelope synthesis and stress responses. Genes encoding membrane transport proteins from the ATP binding cassette superfamily were the most significantly induced or repressed in COE tolerant mutants compared to the wild type when exposed to COEs. Additionally, differences in the membrane localization of a lipophilic dye in E. faecalis exposed to COEs suggested that resistance was associated with lipid rearrangement in the cell membrane. The membrane adaptation to COEs in EFC3C and EFC3Py resulted in an improved tolerance to bile salt and sodium chloride stress. Overall, this study showed that bacterial cell membranes are the primary target of COEs and that E. faecalis adapts to membrane interacting COE molecules by both lipid rearrangement and changes in membrane transporter activity. The level of resistance to COEs suggests that E. faecalis does not have a specific response pathway to elicit resistance against these molecules and this is supported by the rather broad and diverse suite of genes that are induced upon COE exposure as well as cross-resistance to membrane perturbing stressors.
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A novel conjugated oligoelectrolyte (COE) material, named S6, is designed to have a lipid-bilayer stabilizing topology afforded by an extended oligophenylenevinylene backbone. S6 intercalates biological membranes acting as a hydrophobic support for glycerophospholipid acyl chains. Indeed, Escherichia coli treated with S6 exhibits a twofold improvement in butanol tolerance, a relevant feature to achieve within the general context of modifying microorganisms used in biofuel production. Filamentous growth, a morphological stress response to butanol toxicity in E. coli, is observed in untreated cells after incubation with 0.9% butanol (v/v), but is mitigated by S6 treatment. Real-time fluorescence imaging using giant unilamellar vesicles reveals the extent to which S6 counters membrane instability. Moreover, S6 also reduces butanol-induced lipopolysaccharide release from the outer membrane to further maintain cell integrity. These findings highlight a deliberate effort in the molecular design of a chain-elongated COE to stabilize microbial membranes against environmental challenges.
Assuntos
Parede Celular/efeitos dos fármacos , Eletrólitos/farmacologia , Compostos de Vinila/química , Butanóis/toxicidade , Parede Celular/metabolismo , Eletrólitos/química , Escherichia coli/efeitos dos fármacos , Escherichia coli/metabolismo , Lipopolissacarídeos/química , Testes de Sensibilidade Microbiana , Microscopia ConfocalRESUMO
A three-dimensional conjugated oligoelectrolyte (COE) bearing a [2.2]paracyclophane unit (COE2-3-pCp) was synthesized. Its biological activity was determined both in vivo and in silico within the context of membrane perturbation and biocompatibility. Molecular dynamics simulations indicate that, compared to its linear analog (COE2-3C), COE2-3-pCp introduces more lipid disorder with higher extent of membrane thinning. COE2-3-pCp also exhibits a higher MIC towards E. coli K12 and yeast, while maintaining similar levels of membrane permeabilization. These findings suggest a new design of COEs as biocompatible cell permeabilizers.
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The growing problem of antibiotic resistant bacteria, along with a dearth of new antibiotics, has redirected attention to the search for alternative antimicrobial agents. Conjugated oligoelectrolytes (COEs) are an emerging class of antimicrobial agents which insert into bacterial cell membranes and are inhibitory against a range of Gram-positive and Gram-negative bacteria. In this study, the extent of COE resistance that Enterococcus faecalis could achieve was studied. Enterococci are able to grow in hostile environments and develop resistance to membrane targeting antibiotics such as daptomycin in clinical settings. Herein we expand our knowledge of the antimicrobial mechanism of action of COEs by developing COE-resistant strains of E. faecalis OG1RF. Evolution studies yielded strains with a moderate 4-16 fold increase in antimicrobial resistance relative to the wild type. The resistant isolates accumulated agent-specific mutations associated with the liaFSR operon, which is a cell envelope-associated stress-response sensing and regulating system. The COE resistant isolates displayed significantly altered membrane fatty acid composition. Subsequent, exogenous supplementation with single fatty acids, which were chosen based on those dominating the fatty acid profiles of the mutants, increased resistance of the wild-type E. faecalis to COEs. In combination, genetic, fatty acid, and uptake studies support the hypothesis that COEs function through insertion into and disruption of membranes and that the mechanism by which this occurs is specific to the disrupting agent. These results were validated by a series of biophysical experiments showing the tendency of COEs to accumulate in and perturb adapted membrane extracts. Collectively, the data support that COEs are promising antimicrobial agents for targeting E. faecalis, and that there is a high barrier to the emergence of severely resistant strains constrained by biological limits of membrane remodeling that can occur in E. faecalis.
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Conjugated oligoelectrolytes (COEs) with phenylenevinylene (PV) repeat units are known to spontaneously intercalate into cell membranes. Twelve COEs, including seven structures reported here for the first time, were investigated for the relationship between their membrane disrupting properties and structural modifications, including the length of the PV backbone and the presence of either a tetraalkylammonium or a pyridinium ionic pendant group. Optical characteristics and interactions with cell membranes were determined using UV-Vis absorption and photoluminescence spectroscopies, and confocal microscopy. Toxicity tests on representative Gram-positive (Enterococcus faecalis) and Gram-negative (Escherichia coli) bacteria reveal generally greater toxicity to E. faecalis than to E. coli and indicate that shorter molecules have superior antimicrobial activity. Increased antimicrobial potency was observed in three-ring COEs appended with pyridinium ionic groups but not with COEs with four or five PV repeat units. Studies with mutants having cell envelope modifications indicate a possible charge based interaction with pyridinium-appended compounds. Fluorine substitutions on COE backbones result in structures that are less toxic to E. coli, while the addition of benzothiadiazole to COE backbones has no effect on increasing antimicrobial function. A weakly membrane-intercalating COE with only two PV repeat units allowed us to determine the synthetic limitations as a result of competition between solubility in aqueous media and association with cell membranes. We describe, for the first time, the most membrane disrupting structure achievable within two homologous series of COEs and that around a critical three-ring backbone length, structural modifications have the most effect on antimicrobial activity.
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Low-cost and rapid detection of volatile organic compounds (VOCs) is important for the control of water quality of used water and protection of downstream used water treatment processes. In this work, the effect of sub-toxic concentration of VOCs on the current output of Escherichia coli in bioelectrochemical systems (BES) is shown, in light of environmental sensing applications for sewage and used water networks. E. coli cells were grown on carbon felt electrodes in artificial used water, to increase sensitivity and decrease response time for detection. Extracellular electron transfer was promoted by the addition of a biocompatible redox mediator, 2-hydroxy-1,4-naphthoquinone (HNQ). Among the eight VOCs investigated, toluene is the most toxic to E. coli, with a detection limit of 50±2mgL(-1) and current output of 32±1nAmg(-1)L(-1). This work offers a straightforward route to enhance the detection of organic contaminants in used water for environmental applications.
Assuntos
Escherichia coli/efeitos dos fármacos , Escherichia coli/metabolismo , Espaço Extracelular/efeitos dos fármacos , Espaço Extracelular/metabolismo , Compostos Orgânicos Voláteis/toxicidade , Poluentes Químicos da Água/toxicidade , Proliferação de Células/efeitos dos fármacos , Relação Dose-Resposta a Droga , Condutividade Elétrica , Eletroquímica , Eletrodos , Escherichia coli/citologiaRESUMO
Volatile organic compounds (VOCs) are commonly used as solvents in various industrial settings. Many of them present a challenge to receiving environments, due to their toxicity and low bioavailability for degradation. Microorganisms are capable of sensing and responding to their surroundings and this makes them ideal detectors for toxic compounds. This study investigates the global transcriptomic responses of Escherichia coli K-12 to selected VOCs at sub-toxic levels. Cells grown in the presence of VOCs were harvested during exponential growth, followed by whole transcriptome shotgun sequencing (RNAseq). The analysis of the data revealed both shared and unique genetic responses compared to cells without exposure to VOCs. Results suggest that various functional gene categories, for example, those relating to Fe/S cluster biogenesis, oxidative stress responses and transport proteins, are responsive to selected VOCs in E. coli. The differential expression (DE) of genes was validated using GFP-promoter fusion assays. A variety of genes were differentially expressed even at non-inhibitory concentrations and when the cells are at their balanced-growth. Some of these genes belong to generic stress response and others could be specific to VOCs. Such candidate genes and their regulatory elements could be used as the basis for designing biosensors for selected VOCs.