The effect of toluene on the structure and permeability of the outer and cytoplasmic membranes of Escherichia coli

Synergistic Effects of Microplastics and Marine Pollutants on the Destabilization of Lipid Bilayers

Microplastics have been detected in diverse environments, including soil, snowcapped mountains, and even within human organs and blood. These findings have sparked extensive research into the health implications of microplastics for living organisms. Recent studies have shown that microplastics can adsorb onto lipid membranes and induce mechanical stress. In controlled laboratory conditions, the behavior and effects of microplastics can differ markedly from those in natural environments. In this study, we investigate how exposure of microplastics to pollutants affects their interactions with lipid bilayers. Our findings reveal that pollutants, such as chemical solvents, significantly enhance the mechanical stretching effects of microplastics. This suggests that microplastics can act as vectors for harmful pollutants, facilitating their penetration through lipid membranes and thus strongly affect their biophysical properties. This research underscores the complex interplay between microplastics and environmental contaminants.

A multi-functional reagent suitable for 1-step rapid DNA intercalation fluorescence-based screening of total bacteria in drinking water

The prerequisites for rapid screening of total bacteria in drinking water are low detection limit and convenience. Inspired by commercial adenosine 5'-triphosphate (ATP) based total bacterial detection kits, we pursued likewise convenience but with much lower detection limit. Existing intercalation fluorescence-based techniques employ multiple reagents to permeate the cell membrane and intercalate dye into the DNA in discrete sequential steps. A simple multi-functional reagent is proposed to do the same within one step. Surfactants (TritonX and SDS), and intercalating dyes (SYBR green, SYBR gold) were examined for their mutual compatibility and augmented with EDTA. Evaluation was performed with Gram negative Escherichia coli K12 (E. coli K12) and Gram positive Bacillus subtilis (B. subtilis) at serial dilution ratios from 10^-6 to 10^-2. Comparison was made with absorbance (600 nm) measurements and a commercial ATP kit. Using charge integrated photodetection, the proposed 1-step reagent achieved an LOD (1.00 × 10^-6, B. subtilis) that is two orders of magnitude lower than that of ATP kit (LOD = 1.06× 10^-4). This means it could detect minute quantity of total bacteria that is otherwise undetected by the ATP kit.

Enhancement of triterpene production via in situ extractive fermentation of Sanghuangporus vaninii YC-1

There have been many studies on the activities and polysaccharide production of Sanghuangporus vaninii. However, few studies have looked at triterpene production from S. vaninii using liquid-state fermentation. A method for enhancing the production of triterpenes by in situ extractive fermentation (ISEF) was studied. Eight solvents were investigated as extractants for triterpene production in the ISEF system. The results showed that using vegetable oil as an extractant significantly increased the yield of total triterpenes and biomass of S. vaninii YC-1, reaching 18.98 ± 0.71 and 44.67 ± 2.21 g/L, respectively. In 5 L fermenter experiments, the added vegetable oil improved the dissolved oxygen condition of the fermentation broth and promoted the growth of S. vaninii YC-1. Furthermore, adding vegetable oil increased the expression of fatty acid synthesis-related genes such as FAD2 and SCD, thereby increasing the synthesis of unsaturated fatty acids in the cell membrane of S. vaninii YC-1. Therefore, the cell membrane permeability of S. vaninii YC-1 increased by 19%. Our results indicated that vegetable oil increased the permeability of S. vaninii YC-1 cell membranes to promote the production of total triterpenes. The use of vegetable oil as an extractant was thus effective in increasing the yield of triterpenes in the ISEF system.

Insight into the impacts and mechanisms of ketone stress on the antibiotic resistance in Escherichia coli

Accumulation of toxic organic has posed a substantial pressure on the proliferation of bacterial resistance. While aromatic organics have been demonstrated to enhance the antibiotic resistance in bacteria, no information is yet available on the effects of non-aromatic organics on the variations of bacterial resistance. Here, we investigated the effects of a typical ketone (i.e., methylisobutanone (MIBK)) on the variations of antibiotic resistance in Escherichia coli (E. coli). The results showed that the growth of resistant E. coli under environmental concentration of 50 μg/L MIBK was firstly inhibited as explained by the transient disruption in the cell membrane and then recovered possibly due to the reactive oxygen species. Exposure to 50 μg/L MIBK gradually raised the abundance of representative resistance gene (ampR) in E. coli. In contrast, the high concentration of 50 mg/L MIBK continuously inhibited the growth of resistant E. coli by disrupting cell membrane and notably promoted the proliferation of ampR through enhancing the horizontal transformation and up-regulating the expression of efflux pump gene. These findings provided the first evidence for the evolution of bacterial resistance in response to ketone organics.

The Role of Lipid Chains as Determinants of Membrane Stability in the Presence of Styrene

Biofermentative production of styrene from renewable carbon sources is crucially dependent on strain tolerance and viability at elevated styrene concentrations. Solvent-driven collapse of bacterial plasma membranes limits yields and is technologically restrictive. Styrene is a hydrophobic solvent that readily partitions into the membrane interior and alters membrane-chain order and packing. We investigate styrene incorporation into model membranes and the role lipid chains play as determinants of membrane stability in the presence of styrene. MD simulations reveal styrene phase separation followed by irreversible segregation into the membrane interior. Solid state NMR shows committed partitioning of styrene into the membrane interior with persistence of the bilayer phase up to 67 mol % styrene. Saturated-chain lipid membranes were able to retain integrity even at 80 mol % styrene, whereas in unsaturated lipid membranes, we observe the onset of a non-bilayer phase of small lipid aggregates in coexistence with styrene-saturated membranes. Shorter-chain saturated lipid membranes were seen to tolerate styrene better, which is consistent with observed chain length reduction in bacteria grown in the presence of small molecule solvents. Unsaturation at mid-chain position appears to reduce the membrane tolerance to styrene and conversion from cis- to trans-chain unsaturation does not alter membrane phase stability but the lipid order in trans-chains is less affected than cis.

Transmembrane penetration mechanism of cyclic pollutants inspected by molecular dynamics and metadynamics: the case of morpholine, phenol, 1,4-dioxane and oxane

The presence of industrially produced chemicals in water is often not monitored, while their passive transport and accumulation can cause serious damage in living cells. Molecular dynamics simulations are an effective way to understand the mechanism of the action of these pollutants. In this paper, the passive membrane transport of 1,4-dioxane, phenol, oxane and morpholine was investigated and analyzed thoroughly from structural and energetic points of view. Free energy profiles for pollutant and water penetration into the bilayer were obtained from well-tempered metadynamics (WT-MD) simulations and a mass density-based approach. It was found that all four investigated compounds can penetrate biological membranes and affect the free energy profile of water penetration. Out of the investigated species, oxane has the thermodynamically most preferred position in the bilayer center, leading to a lower free energy barrier of water molecules by 3 kJ mol-1, resulting in 5 times more water molecules in the bilayer center. The concentration dependence of free energy was tested at two different phenol concentrations using WT-MD, and it was found that the higher phenol concentration lowers the main barrier by 3 kJ mol-1. Density-based free energy calculations were found to reproduce the results of WT-MD within the limits of chemical accuracy.

Fructooligosaccharides production by immobilized Pichia pastoris cells expressing Schedonorus arundinaceus sucrose:sucrose 1-fructosyltransferase

Fructooligosaccharides (FOSs)—fructose-based oligosaccharides—are typical prebiotics with health-promoting effects in humans and animals. The trisaccharide 1-kestotriose is the most attractive inulin-type FOS. We previously reported a recombinant sucrose:sucrose 1-fructosyltransferase (1-SST, EC 2.4.1.99) from Schedonorus arundinaceus (Sa) that efficiently converts sucrose into 1-kestotriose. In this study, Pichia pastoris PGFT6x-308 constitutively expressing nine copies of the Sa1-SST gene displayed fructosyltransferase activity in undisrupted biomass (49.8 U/ml) and culture supernatant (120.7 U/ml) in fed-batch fermentation (72 hr) with sugarcane molasses. Toluene permeabilization increased 2.3-fold the Sa1-SSTrec activity of whole cells entrapped in calcium-alginate beads. The reaction with refined or raw sugar (600 g/l) yielded 1-kestotriose and 1,1-kestotetraose in a ratio of 8:2 with their sum representing above 55% (wt/wt) of total carbohydrates. The FOSs yield decreased to 45% (wt/wt) when sugarcane syrup and molasses were used as cheaper sucrose sources. The beads retained 80% residual Sa1-SSTrec activity after a 30-day batchwise operation with refined cane sugar at 30°C and pH 5.5. The immobilized biocatalyst is attractive for the continuous production of short-chain FOSs, most particularly 1-kestotriose.

Membrane Stability in the Presence of Methacrylate Esters

Bioproduction of poly(methyl methacrylate) is a fast growing global industry that is limited by cellular toxicity of monomeric methacrylate intermediates to the producer strains. Maintaining high methacrylate concentrations during biofermentation, required by economically viable technologies, challenges bacterial membrane stability and cellular viability. Studying the stability of model lipid membranes in the presence of methacrylates offers unique molecular insights into the mechanisms of methacrylate toxicity, as well as into the fundamental structural bases of membrane assembly. We investigate the structure and stability of model membranes in the presence of high levels of methacrylate esters using solid-state nuclear magnetic resonance (NMR) and small-angle X-ray scattering (SAXS). Wide-line ³¹P NMR spectroscopy shows that butyl methacrylate (BMA) can be incorporated into the lipid bilayer at concentrations as high as 75 mol % without significantly disrupting membrane integrity and that lipid acyl chain composition can influence membrane tolerance and ability to accommodate BMA. Using high resolution ¹³C magic angle spinning (MAS) NMR, we show that the presence of 75 mol % BMA lowers the lipid main transition temperature by over 12 degrees, which suggests that BMA intercalates between the lipid chains, causing uncoupling of collective lipid motions that are typically dominated by chain trans-gauche isomerization. Potential uncoupling of the bilayer leaflets to accommodate a separate BMA subphase was not supported by the SAXS experiments, which showed that membrane thickness remained unchanged even at 80% BMA. Reduced X-ray scattering contrast at the polar/apolar interface suggests BMA localization in that region between the lipid molecules.

Design and engineering of whole-cell biocatalytic cascades for the valorization of fatty acids

This review presents the key factors to construct a productive whole-cell biocatalytic cascade exemplified for the biotransformation of renewable fatty acids.

Co-contaminant effects on 1,4-dioxane biodegradation in packed soil column flow-through systems

Biodegradation of 1,4-dioxane was examined in packed quartz and soil column flow-through systems. The inhibitory effects of co-contaminants, specifically trichloroethene (TCE), 1,1-dichloroethene (1,1-DCE), and copper (Cu²⁺) ions, were investigated in the columns either with or without bioaugmentation with a 1,4-dioxane degrading bacterium Pseudonocardia dioxanivorans CB1190. Results indicate that CB1190 cells readily grew and colonized in the columns, leading to significant degradation of 1,4-dioxane under oxic conditions. Degradation of 1,4-dioxane was also observed in the native soil (without bioaugmentation), which had been previously subjected to enhanced reductive dechlorination treatment for co-contaminants TCE and 1,1-DCE. Bioaugmentation of the soil with CB1190 resulted in nearly complete degradation at influent concentrations of 3-10 mg L^-1 1,4-dioxane and a residence reaction time of 40-80 h, but the presence of co-contaminants, 1,1-DCE and Cu²⁺ ions (up to 10 mg L^-1), partially inhibited 1,4-dioxane degradation in the untreated and bioaugmented soil columns. However, the inhibitory effects were much less severe in the column flow-through systems than those previously observed in planktonic cultures, which showed near complete inhibition at the same co-contaminant concentrations. These observations demonstrate a low susceptibility of soil microbes to the toxicity of 1,1-DCE and Cu²⁺ in packed soil flow-through systems, and thus have important implications for predicting biodegradation potential and developing sustainable, cost-effective technologies for in situ remediation of 1,4-dioxane contaminated soils and groundwater.

Novel sanitization approach based on synergistic action of UV-A light and benzoic acid: Inactivation mechanism and a potential application in washing fresh produce

Antimicrobial activity of the simultaneous UV-A light and benzoic acid (BA) treatment against stationary phase Escherichia coli O157:H7 was investigated. While 15 mM BA or UV-A light exposure for 30 min alone caused < 1 logarithmic reduction in the bacterial population, > 5 logarithmic reductions were induced by the simultaneous application of UV-A and 15 mM BA in 30 min, demonstrating a synergistic antimicrobial effect. Due to its ability to increase cell membrane permeability, addition of EDTA (1 mM) was able to decrease the required concentration of BA in the simultaneous treatment from 15 to 8 mM. Microbial inactivation was a result of simultaneous membrane damage, intracellular acidification, and intracellular oxidative stress. The simultaneous treatment was effective in the presence of organic load of up to 500 mg/L of chemical oxygen demand (COD) and was able to lower cross-contamination risk during simulated washing of spinach (Spinacia oleracea) without adversely affecting its color.

Design of experiments-based high-throughput strategy for development and optimization of efficient cell disruption protocols

Efficient and reproducible cell lysis is a crucial step during downstream processing of intracellular products. The composition of an optimal lysis buffer should be chosen depending on the organism, its growth status, the applied detection methods, and even the target molecule. Especially for high-throughput applications, where sample volumes are limited, the adaptation of a lysis buffer to the specific campaign is an urgent need. Here, we present a general design of experiments-based strategy suitable for eight constituents and demonstrate the strength of this approach by the development of an efficient lysis buffer for Gram-negative bacteria, which is applicable in a high-throughput format in a short time. The concentrations of four lysis-inducing chemical agents EDTA, lysozyme, Triton X-100, and polymyxin B were optimized for maximal soluble protein concentration and ß-galactosidase activity in a 96-well format on a Microlab Star liquid handling platform under design of experiments methodology. The resulting lysis buffer showed the same performance as a commercially available lysis buffer. The developed protocol resulted in an optimized buffer within only three runs. The established procedure can be easily applied to adapt the lysis buffer to other strains and target molecules.

Biodegradation Kinetics of 1,4-Dioxane in Chlorinated Solvent Mixtures

This study investigated the impacts of individual chlorinated solvents and their mixtures on aerobic 1,4-dioxane biodegradation by Pseudonocardia dioxanivorans CB1190. The established association of these co-occurring compounds suggests important considerations for their respective biodegradation processes. Our kinetics and mechanistic studies demonstrated that individual solvents inhibited biodegradation of 1,4-dioxane in the following order: 1,1-dichloroethene (1,1-DCE) > cis-1,2-diochloroethene (cDCE) > trichloroethene (TCE) > 1,1,1-trichloroethane (TCA). The presence of 5 mg L(-1) 1,1-DCE completely inhibited 1,4-dioxane biodegradation. Subsequently, we determined that 1,1-DCE was the strongest inhibitor of 1,4-dioxane biodegradation by bacterial pure cultures exposed to chlorinated solvent mixtures as well as in environmental samples collected from a site contaminated with chlorinated solvents and 1,4-dioxane. Inhibition of 1,4-dioxane biodegradation rates by chlorinated solvents was attributed to delayed ATP production and down-regulation of both 1,4-dioxane monooxygenase (dxmB) and aldehyde dehydrogenase (aldH) genes. Moreover, increasing concentrations of 1,1-DCE and cis-1,2-DCE to 50 mg L(-1) respectively increased 5.0-fold and 3.5-fold the expression of the uspA gene encoding a universal stress protein. In situ natural attenuation or enhanced biodegradation of 1,4-dioxane is being considered for contaminated groundwater and industrial wastewater, so these results will have implications for selecting 1,4-dioxane bioremediation strategies at sites where chlorinated solvents are present as co-contaminants.

Effect of Tween 80 and Acetone on the Secretion, Structure and Antioxidant Activities of Exopolysaccharides from Lentinus tigrinus

In this study, the effects of the addition of Tween 80 and acetone on secretion, structure and antioxidant activities of Lentinus tigrinus exopolysaccharides (EPS) were investigated. It was found that Tween 80 and acetone displayed a stimulatory effect on EPS secretion. The EPS obtained by the addition of Tween 80 (EPS-T), acetone (EPS-A) and control (EPS--C) were purified by Sepharose CL-6B gel filtration chromatography and molecular mass of purified fractions was estimated to be 22.1, 137 and 12 kDa, respectively. Monosaccharide composition analysis indicated that EPS-T, EPS-A and EPS-C were mainly composed of glucose and mannose. Congo Red test indicated that EPS-T and EPS-A had a highly ordered conformation of triple helix, while EPS-C had a random coil conformation. Furthermore, EPS-A exhibited higher DPPH scavenging and antiproliferative activities than EPS--C and EPS-T, which might be attributed to the molecular mass.

Antibacterial Activity of Juglone against Staphylococcus aureus: From Apparent to Proteomic

The proportion of foodborne disease caused by pathogenic microorganisms is rising worldwide, with staphylococcal food poisoning being one of the main causes of this increase. Juglone is a plant-derived 1,4-naphthoquinone with confirmed antibacterial and antitumor activities. However, the specific mechanism underlying its antibacterial activity against Staphylococcus aureus remains unclear. To elucidate the mechanism underlying its antibacterial activity, isobaric tags for relative and absolute quantitation methods of quantitative proteomics were applied for analysis of the 53 proteins that were differentially expressed after treatment with juglone. Combined with verification experiments, such as detection of changes in DNA and RNA content and quantification of oxidative damage, our results suggested that juglone effectively increased the protein expression of oxidoreductase and created a peroxidative environment within the cell, significantly reducing cell wall formation and increasing membrane permeability. We hypothesize that juglone binds to DNA and reduces DNA transcription and replication directly. This is the first study to adopt a proteomic approach to investigate the antibacterial mechanism of juglone.

Metabolic Fingerprinting of Pseudomonas putida DOT-T1E Strains: Understanding the Influence of Divalent Cations in Adaptation Mechanisms Following Exposure to Toluene

Pseudomonas putida strains can adapt and overcome the activity of toxic organic solvents by the employment of several resistant mechanisms including efflux pumps and modification to lipopolysaccharides (LPS) in their membranes. Divalent cations such as magnesium and calcium play a crucial role in the development of solvent tolerance in bacterial cells. Here, we have used Fourier transform infrared (FT-IR) spectroscopy directly on cells (metabolic fingerprinting) to monitor bacterial response to the absence and presence of toluene, along with the influence of divalent cations present in the growth media. Multivariate analysis of the data using principal component-discriminant function analysis (PC-DFA) showed trends in scores plots, illustrating phenotypic alterations related to the effect of Mg(2+), Ca(2+) and toluene on cultures. Inspection of PC-DFA loadings plots revealed that several IR spectral regions including lipids, proteins and polysaccharides contribute to the separation in PC-DFA space, thereby indicating large phenotypic response to toluene and these cations. Finally, the saturated fatty acid ratio from the FT-IR spectra showed that upon toluene exposure, the saturated fatty acid ratio was reduced, while it increased in the presence of divalent cations. This study clearly demonstrates that the combination of metabolic fingerprinting with appropriate chemometric analysis can result in practicable knowledge on the responses of important environmental bacteria to external stress from pollutants such as highly toxic organic solvents, and indicates that these changes are manifest in the bacterial cell membrane. Finally, we demonstrate that divalent cations improve solvent tolerance in P. putida DOT‑T1E strains.

Isolation, characterization and community diversity of indigenous putative toluene-degrading bacterial populations with catechol-2,3-dioxygenase genes in contaminated soils

Indigenous bacterial assemblages with putative hydrocarbon-degrading capabilities were isolated, characterized and screened for the presence of the catechol-2,3-dioxygenase (C23O) gene after exposure to toluene in two different (i.e., pristine and conditioned) soil communities. The indigenous bacterial populations were exposed to the hydrocarbon substrate by the addition of toluene concentrations, ranging from 0.5 % to 10 % V/W in 10 g of each soil and incubated at 30 °C for upwards of 12 days. In total, 25 isolates (11 in pristine soil and 14 in conditioned soil) were phenotypically characterized according to standard microbiological methods and also screened for the 238-bp C23O gene fragment. Additionally, 16S rRNA analysis of the isolates identified some of them as belonging to the genera Bacillus, Exiguobacterium, Enterobacter, Pseudomonas and Stenotrophomonas. Furthermore, the two clone libraries that were constructed from these toluene-contaminated soils also revealed somewhat disparate phylotypes (i.e., 70 % Actinobacteria and Firmicutes to 30 % Proteobacteria in conditioned soil, whereas in pristine soil: 66 % Actinobacteria and Firmicutes; 21 % Proteobacteria and 13 % Bacteroidetes). The differences observed in bacterial phylotypes between these two soil communities may probably be associated with previous exposure to hydrocarbon sources by indigenous populations in the conditioned soil as compared to the pristine soil.

Oxidative stress response in Pseudomonas putida

Pseudomonas putida is widely distributed in nature and is capable of degrading various organic compounds due to its high metabolic versatility. The survival capacity of P. putida stems from its frequent exposure to various endogenous and exogenous oxidative stresses. Oxidative stress is an unavoidable consequence of interactions with various reactive oxygen species (ROS)-inducing agents existing in various niches. ROS could facilitate the evolution of bacteria by mutating genomes. Aerobic bacteria maintain defense mechanisms against oxidative stress throughout their evolution. To overcome the detrimental effects of oxidative stress, P. putida has developed defensive cellular systems involving induction of stress-sensing proteins and detoxification enzymes as well as regulation of oxidative stress response networks. Genetic responses to oxidative stress in P. putida differ markedly from those observed in Escherichia coli and Salmonella spp. Two major redox-sensing transcriptional regulators, SoxR and OxyR, are present and functional in the genome of P. putida. However, the novel regulators FinR and HexR control many genes belonging to the E. coli SoxR regulon. Oxidative stress can be generated by exposure to antibiotics, and iron homeostasis in P. putida is crucial for bacterial cell survival during treatment with antibiotics. This review highlights and summarizes current knowledge of oxidative stress in P. putida, as a model soil bacterium, together with recent studies from molecular genetics perspectives.

Microbial degradation of alkenylbenzenes

Alkenylbenzenes are produced in large quantities by the petrochemical industry. The simplest of these alkenylbenzenes, styrene, is in widespread use in the polymer-processing industry and is thus found in many industrial effluents. Airborne gaseous emissions of styrene are particular problems due to the potential toxicity and carcinogenicity of the compound. The catabolic pathways involved in the degradation of styrene have been well characterised. With an increased knowledge of the adaptative response which microorganisms exhibit when exposed to higher styrene concentrations, together with an understanding of the genetic regulation of the catabolic pathways which operate in these microbial strains, it is likely that these organisms could be exploited in areas such as biotransformations, biocatalysis and bioremediation.

Transcriptome response to alkane biofuels in Saccharomyces cerevisiae: identification of efflux pumps involved in alkane tolerance

BACKGROUND

Hydrocarbon alkanes have been recently considered as important next-generation biofuels because microbial production of alkane biofuels was demonstrated. However, the toxicity of alkanes to microbial hosts can possibly be a bottleneck for high productivity of alkane biofuels. To tackle this toxicity issue, it is essential to understand molecular mechanisms of interactions between alkanes and microbial hosts, and to harness these mechanisms to develop microbial host strains with improved tolerance against alkanes. In this study, we aimed to improve the tolerance of Saccharomyces cerevisiae, a model eukaryotic host of industrial significance, to alkane biofuels by exploiting cellular mechanisms underlying alkane response.

RESULTS

To this end, we first confirmed that nonane (C9), decane (C10), and undecane (C11) were significantly toxic and accumulated in S. cerevisiae. Transcriptome analyses suggested that C9 and C10 induced a range of cellular mechanisms such as efflux pumps, membrane modification, radical detoxification, and energy supply. Since efflux pumps could possibly aid in alkane secretion, thereby reducing the cytotoxicity, we formed the hypothesis that those induced efflux pumps could contribute to alkane export and tolerance. In support of this hypothesis, we demonstrated the roles of the efflux pumps Snq2p and Pdr5p in reducing intracellular levels of C10 and C11, as well as enhancing tolerance levels against C10 and C11. This result provided the evidence that Snq2p and Pdr5p were associated with alkane export and tolerance in S. cerevisiae.

CONCLUSIONS

Here, we investigated the cellular mechanisms of S. cerevisiae response to alkane biofuels at a systems level through transcriptome analyses. Based on these mechanisms, we identified efflux pumps involved in alkane export and tolerance in S. cerevisiae. We believe that the results here provide valuable insights into designing microbial engineering strategies to improve cellular tolerance for highly efficient alkane biofuel production.

Transcriptional control of the main aromatic hydrocarbon efflux pump in Pseudomonas

Bacteria of the species Pseudomonas putida are ubiquitous soil inhabitants, and a few strains are able to thrive in the presence of extremely high concentrations of toxic solvents such as toluene and related aromatic hydrocarbons. Toluene tolerance is multifactorial in the sense that bacteria use a wide range of physiological and genetic changes to overcome solvent damage. This includes enhanced membrane impermeabilization through cis to trans isomerization of unsaturated fatty acids, activation of a stress response programme, and induction of efflux pumps that expulse toxic hydrocarbons to the outer medium. The most relevant element in this toluene tolerance arsenal is the TtgGHI efflux pump controlled by the TtgV regulator. We discuss here how TtgV controls expression of this efflux pump in response to solvents.

Glycosylation is required for outer membrane localization of the lectin LecB in Pseudomonas aeruginosa

The fucose-/mannose-specific lectin LecB from Pseudomonas aeruginosa is transported to the outer membrane; however, the mechanism used is not known so far. Here, we report that LecB is present in the periplasm of P. aeruginosa in two variants of different sizes. Both were functional and could be purified by their affinity to mannose. The difference in size was shown by a specific enzyme assay to be a result of N glycosylation, and inactivation of the glycosylation sites was shown by site-directed mutagenesis. Furthermore, we demonstrate that this glycosylation is required for the transport of LecB.

Multiple responses of gram-positive and gram-negative bacteria to mixture of hydrocarbons

Most of our knowledge about pollutants and the way they are biodegraded in the environment has previously been shaped by laboratory studies using hydrocarbon-degrading bacterial strains isolated from polluted sites. In present study Gram-positive (Mycobacterium sp. IBBPo1, Oerskovia sp. IBBPo2, Corynebacterium sp. IBBPo3) and Gram-negative (Chryseomonas sp. IBBPo7, Pseudomonas sp. IBBPo10, Burkholderia sp. IBBPo12) bacteria, isolated from oily sludge, were found to be able to tolerate pure and mixture of saturated hydrocarbons, as well as pure and mixture of monoaromatic and polyaromatic hydrocarbons. Isolated Gram-negative bacteria were more tolerant to mixture of saturated (n-hexane, n-hexadecane, cyclohexane), monoaromatic (benzene, toluene, ethylbenzene) and polyaromatic (naphthalene, 2-methylnaphthalene, fluorene) hydrocarbons than Gram-positive bacteria. There were observed cellular and molecular modifications induced by mixture of saturated, monoaromatic and polyaromatic hydrocarbons to Gram-positive and Gram-negative bacteria. These modifications differ from one strain to another and even for the same bacterial strain, according to the nature of hydrophobic substrate.

Cell Envelope Changes in Solvent-Tolerant and Solvent-Sensitive Pseudomonas putida Strains following Exposure to o-Xylene

Solvent-tolerant and -sensitive Pseudomonas putida strains were studied to determine their cell envelope changes following exposure to o-xylene. Both strains produced trans-unsaturated fatty acids. The tolerant strain showed an increase in total fatty acids, an increase in saturated fatty acids, and modified lipopolysaccharide. It is suggested that these envelope modifications aid in survival at high concentrations of organic solvents.

Bioreduction with efficient recycling of NADPH by coupled permeabilized microorganisms

The glucose dehydrogenase (GDH) from Bacillus subtilis BGSC 1A1 was cloned and functionally expressed in Escherichia coli BL21(pGDH1) and XL-1 Blue(pGDH1). Controlled permeabilization of recombinant E. coli BL21 and XL-1 Blue with EDTA-toluene under optimized conditions resulted in permeabilized cells with specific activities of 61 and 14 U/g (dry weight) of cells, respectively, for the conversion of NADP(+) to NADPH upon oxidation of glucose. The permeabilized recombinant strains were more active than permeabilized B. subtilis BGSC 1A1, did not exhibit NADPH/NADH oxidase activity, and were useful for regeneration of both NADH and NADPH. Coupling of permeabilized cells of Bacillus pumilus Phe-C3 containing an NADPH-dependent ketoreductase and an E. coli recombinant expressing GDH as a novel biocatalytic system allowed enantioselective reduction of ethyl 3-keto-4,4,4-trifluorobutyrate with efficient recycling of NADPH; a total turnover number (TTN) of 4,200 mol/mol was obtained by using E. coli BL21(pGDH1) as the cofactor-regenerating microorganism with initial addition of 0.005 mM NADP(+). The high TTN obtained is in the practical range for producing fine chemicals. Long-term stability of the permeabilized cell couple and a higher product concentration were demonstrated by 68 h of bioreduction of ethyl 3-keto-4,4,4-trifluorobutyrate with addition of 0.005 mM NADP(+) three times; 50.5 mM (R)-ethyl 3-hydroxy-4,4,4-trifluorobutyrate was obtained with 95% enantiomeric excess, 84% conversion, and an overall TTN of 3,400 mol/mol. Our method results in practical synthesis of (R)-ethyl 3-hydroxy-4,4,4-trifluorobutyrate, and the principle described here is generally applicable to other microbial reductions with cofactor recycling.

Physiological and transcriptional responses of Nitrosomonas europaea to toluene and benzene inhibition

Ammonia oxidizing bacteria (AOB) are inhibited by many compounds found in wastewater treatment plant (WWTP) influent, including aromatic hydrocarbons. The detection of "sentinel genes" to identify the presence of aromatic hydrocarbons could be useful to WWTP operators. In this study, the transcriptomic responses of Nitrosomonas europaea during the cometabolism of benzene to phenol and toluene to benzyl alcohol and benzaldehyde were evaluated using whole genome Affymetrix microarrays and qRT-PCR. Benzyl alcohol and benzaldehyde were found not to inhibit N. europaea. However, phenol concentrations as low as 5 microM directly inhibited ammonia oxidation. Surprisingly, there were no significant up- or down-regulation of genes in N. europaea cells exposed to 20 microM toluene, which caused 50% inhibition of ammonia oxidation. Exposing N. europaea to 40 microM benzene, which caused a similar degree of inhibition, resulted in the up-regulation of seven adjacent genes, including NE 1545 (a putative pirin protein) and NE 1546 (a putative membrane protein), that appear to be involved with fatty-acid metabolism, lipid biosynthesis, and membrane protein synthesis. qRT-PCR analysis revealed that NE 1545 and NE 1546 were significantly up-regulated upon exposure to benzene and phenol, but not upon exposure to toluene. Transmission electron microscope images revealed a shift in outer cell structure in response to benzene exposure.

Adaptation of Rhodococcus erythropolis cells to high concentrations of toluene

Cells of Rhodococcus erythropolis DCL14 were adapted to increasing toluene concentrations in a mechanically stirred reactor. When the initial non-adapted cells were placed in contact with toluene, only 10.5% of cells remained viable after 1 h in the presence of 20% (v/v) toluene, while 8.6% of cells were viable after 28 h in the presence of an organic phase containing 80% (v/v) toluene in n-dodecane. Cell adaptation was studied by following the toluene consumption rate, the viability of the cell population, and the composition of the bacteria cellular membrane in the presence of increasing concentrations of toluene in the reactor. A maximum toluene concentration of 4.9 M, which corresponds to 52.4% (v/v) toluene in the organic phase, was achieved, toluene being consumed at 10.7 mg/(h mg protein). The adapted cells showed a substantially increased resistance to 50% ethanol and to concentrations of Betadine and Micropur tablets currently used in water purification, when compared to non-adapted cells.

Coupling of permeabilized microorganisms for efficient enantioselective reduction of ketone with cofactor recycling

A novel, simple and efficient cofactor recycling method for enantioselective bioreduction has been developed by the use of permeabilized cells of a reductase-containing microorganism and a glucose dehydrogenase-containing microorganism

Entrapment in E. coli improves the operational stability of recombinant β-glycosidase CelB from Pyrococcus furiosus and facilitates biocatalyst recovery

beta-Glycosidase CelB from the hyperthermophilic archaeon Pyrococcus furiosus is a versatile biocatalyst that has been used for the hydrolysis and synthesis of beta-d-glycosidic compounds at high temperatures and in non-conventional solvents. In spite of its outstanding thermal stability, CelB is prone to inactivation in the presence of reducing sugars and through recirculation in loop enzyme reactors. Entrapment into E. coli cells was used here to improve the stability of recombinant CelB under conditions promoting strong inactivation. Glutardialdehyde-mediated protein cross-linking or rigidification of the cell membrane by adding magnesium ions was required to prevent release of CelB from within the cell into the bulk solution. In the presence of 1M glucose or when applying recirculation rates of 2.6 min(-1), the entrapped enzyme was around two-fold more stable at 80 degrees C than free CelB. The significance of the stabilisation was attenuated by the decrease in CelB initial activity which was due to cross-linking and glutardialdehyde concentration-dependent. Entrapment facilitated downstream processing of CelB and biocatalyst recovery in repeated batchwise conversions of lactose at elevated temperatures.

[Rapid and efficient extraction of soluble proteins from gram-negative microorganisms without disruption of cell walls]

The ability of buffer solutions containing low concentrations of nonionic detergents (Triton X-100, Tween 20, Brij 58, and Lubrol PX) and the anionic detergent sodium deoxycholate, as well as mixtures of these detergents with chaeotropes (urea and guanidine hydrochloride), to extract intracellular proteins of Gram-negative microorganisms (Escherichia coli and Pseudomonas aeruginosa) was studied. It was established that the solutions containing Triton X-100 and sodium deoxycholate and the mixtures of these detergents with urea are the most effective. It was shown that the extraction of proteins from bacterial cells under the studied conditions is not accompanied by a release of DNA into solution but is associated with extraction of low-molecular RNAs. The level of protein extraction reaches 80%. No disruption of the bacterial cell wall occurs during the extraction, and proteins probably permeate through meshes of the murein network. The efficiencies of our buffer mixtures are close to or higher than that of the commercial reagent CelLytic B (Sigma, United States). The practical uses of the chaeotropic mixtures developed are discussed.

The RpoT regulon of Pseudomonas putida DOT-T1E and its role in stress endurance against solvents

Pseudomonas putida encodes 20 extracytoplasmic sigma factors (ECFs). In this study, we show that one of these ECFs, known as ECF-Pp12 (PP3006), plays a role in tolerance of toluene and other organic solvents. Based on this finding, we have called the gene that encodes this new ECF rpoT. The rpoT gene forms an operon with the preceding gene and with the gene located downstream. The translated gene product of the open reading frame PP3005 is an inner membrane protein, whereas the PP3007 protein is periplasmic. A nonpolar DeltarpoT mutant was generated by homologous recombination, and survival of the mutant was tested under various stress conditions. The mutant strain was hypersensitive to toluene and other solvents but just as tolerant as the wild type of stress imposed by heat, antibiotics, NaCl, paraquat, sodium dodecyl sulfate, H(2)O(2), and benzoate. In the DeltarpoT mutant background, expression of around 50 transcriptional units was affected: 31 cistrons were upregulated, and 23 cistrons were downregulated. This indicates that about 1% of all P. putida genes are under the direct or indirect influence of RpoT. The rpoT gene controls the expression of a number of membrane proteins, including components of the respiratory chains, porins, transporters, and multidrug efflux pumps. Hypersensitivity of the P. putida RpoT-deficient mutant to organic solvents can be attributed to the fact that in the DeltarpoT strain, expression of the toluene efflux pump ttgGHI genes is severalfold lower than in the parental strain.

CYP153A6, a soluble P450 oxygenase catalyzing terminal-alkane hydroxylation

The first and key step in alkane metabolism is the terminal hydroxylation of alkanes to 1-alkanols, a reaction catalyzed by a family of integral-membrane diiron enzymes related to Pseudomonas putida GPo1 AlkB, by a diverse group of methane, propane, and butane monooxygenases and by some membrane-bound cytochrome P450s. Recently, a family of cytoplasmic P450 enzymes was identified in prokaryotes that allow their host to grow on aliphatic alkanes. One member of this family, CYP153A6 from Mycobacterium sp. HXN-1500, hydroxylates medium-chain-length alkanes (C6 to C11) to 1-alkanols with a maximal turnover number of 70 min(-1) and has a regiospecificity of > or =95% for the terminal carbon atom position. Spectroscopic binding studies showed that C6-to-C11 aliphatic alkanes bind in the active site with Kd values varying from approximately 20 nM to 3.7 microM. Longer alkanes bind more strongly than shorter alkanes, while the introduction of sterically hindering groups reduces the affinity. This suggests that the substrate-binding pocket is shaped such that linear alkanes are preferred. Electron paramagnetic resonance spectroscopy in the presence of the substrate showed the formation of an enzyme-substrate complex, which confirmed the binding of substrates observed in optical titrations. To rationalize the experimental observations on a molecular scale, homology modeling of CYP153A6 and docking of substrates were used to provide the first insight into structural features required for terminal alkane hydroxylation.

Miniaturized test system for soil respiration induced by volatile pollutants

A miniaturized method based on 96-well microtitre plates was developed and used to study respiration in pristine and contaminated soils following addition of volatile substrates. Small soil samples were exposed to fuel components, which were volatilized from spatially separate reservoirs of 2,2,4,4,6,8,8-heptamethylnonane (HMN) as an organic carrier. Respiration was determined as CO(2) production by means of a pH-indicator and bicarbonate-containing agar, or as (14)CO(2) evolution from (14)C-labelled substrates. Substrate concentrations inducing maximum microbial activity or inhibition were determined and CO(2) production profiles examined by multivariate analysis. When high concentrations of fuel components were applied, distinction of hydrocarbon exposed soils from unexposed soil was achieved within 6 h of incubation. With low concentrations, adequate distinction was achieved after 24 h, probably as a result of community adaptation. Nutrient limitation was identified with the (14)C method for toluene, and the optimal N and P amendment determined. Further potential applications of this rapid and inexpensive method are outlined.

Proteomic analysis reveals the participation of energy- and stress-related proteins in the response of Pseudomonas putida DOT-T1E to toluene

Pseudomonas putida DOT-T1E is tolerant to toluene and other toxic hydrocarbons through extrusion of the toxic compounds from the cell by means of three efflux pumps, TtgABC, TtgDEF, and TtgGHI. To identify other cellular factors that allow the growth of P. putida DOT-T1E in the presence of high concentrations of toluene, we performed two-dimensional gel analyses of proteins extracted from cultures grown on glucose in the presence and in the absence of the organic solvent. From a total of 531 spots, 134 proteins were observed to be toluene specific. In the absence of toluene, 525 spots were clearly separated and 117 proteins were only present in this condition. Moreover, 35 proteins were induced by at least twofold in the presence of toluene whereas 26 were repressed by at least twofold under these conditions. We reasoned that proteins that were highly induced could play a role in toluene tolerance. These proteins, identified by matrix-assisted laser desorption ionization-time of flight mass spectrometry, were classified into four categories: 1, proteins involved in the catabolism of toluene; 2, proteins involved in the channeling of metabolic intermediates to the Krebs cycle and activation of purine biosynthesis; 3, proteins involved in sugar transport; 4, stress-related proteins. The set of proteins in groups 2 and 3 suggests that the high energy demand required for solvent tolerance is achieved via activation of cell metabolism. The role of chaperones that facilitate the proper folding of newly synthesized proteins under toluene stress conditions was analyzed in further detail. Knockout mutants revealed that CspA, XenA, and Tuf-1 play a role in solvent tolerance in Pseudomonas, although this role is probably not specific to toluene, as indicated by the fact that all mutants grew more slowly than the wild type without toluene.