Orange Carotenoid Protein in Mesoporous Silica: A New System towards the Development of Colorimetric and Fluorescent Sensors for pH and Temperature.

Orange carotenoid protein (OCP) is a photochromic carotenoprotein involved in the photoprotection of cyanobacteria. It is activated by blue-green light to a red form OCPR capable of dissipating the excess of energy of the cyanobacterial photosynthetic light-harvesting systems. Activation to OCPR can also be achieved in the dark. In the present work, activation by pH changes of two different OCPs-containing echinenone or canthaxanthin as carotenoids-is investigated in different conditions. A particular emphasis is put on OCP encapsulated in SBA-15 mesoporous silica nanoparticles. It is known that in these hybrid systems, under appropriate conditions, OCP remains photoactive. Here, we show that when immobilised in SBA-15, the OCP visible spectrum is sensitive to pH changes, but such a colorimetric response is very different from the one observed for OCP in solution. In both cases (SBA-15 matrices and solutions), pH-induced colour changes are related either by orange-to-red OCP activation, or by carotenoid loss from the denatured protein. Of particular interest is the response of OCP in SBA-15 matrices, where a sudden change in the Vis absorption spectrum and in colour is observed for pH changing from 2 to 3 (in the case of canthaxanthin-binding OCP in SBA-15: λMAX shifts from 454 to 508 nm) and for pH changing from 3 to 4 (in the case of echinenone-binding OCP in SBA-15: λMAX shifts from 445 to 505 nm). The effect of temperature on OCP absorption spectrum and colour (in SBA-15 matrices) has also been investigated and found to be highly dependent on the properties of the used mesoporous silica matrix. Finally, we also show that simultaneous encapsulation in selected surface-functionalised SBA-15 nanoparticles of appropriate fluorophores makes it possible to develop OCP-based pH-sensitive fluorescent systems. This work therefore represents a proof of principle that OCP immobilised in mesoporous silica is a promising system in the development of colorimetric and fluorometric pH and temperature sensors.

Copper Nanoparticles Supported on ZIF-8: Comparison of Cu(II) Reduction Processes and Application as Benzyl Alcohol Oxidation Catalysts.

We report the synthesis of a stable heterogeneous catalyst based on copper metal nanoparticles with oxidized surface supported on ZIF-8 for the oxidation of benzyl alcohol under mild temperature and using air as a sustainable oxygen source as well as for the implementation of the tandem "one-pot" catalytic system allowing the sustainable synthesis of benzylidene malononitrile. The influence of the reduction process applied to form the nanoparticle upon the catalyst texture and its performances was extensively examined. After ZIF-8 impregnation with a copper chloride precursor, the reduction of cupric ions into Cu0 nanoparticles was carried out according to two procedures: (i) by soaking the solid into a solution of NaBH4 and (ii) by submitting it to a flow of gaseous H2 at 340 °C. The in-depth physicochemical characterization and comparison of the resulting two types of Cu/ZIF-8 materials reveal significant differences: the reduction with NaBH4 led to the formation of 16 nm sized Cu0 nanoparticles (NP) mainly localized on the external surface of the ZIF-8 crystals together with ZnO nanocrystallites, while the reduction under H2 flow resulted in Cu0 nanoparticles with a mean size of 22 nm embedded within the bulk of ZIF-8 crystals. More, when NaBH4 was used to reduce cupric ions, ZnO particles were highlighted by high-resolution microcospy imaging. Formation of ZnO impurities was confirmed by the photoluminescence analysis of ZIF-8 after NaBH4 treatment. In contrast, ZnO was not detected on ZIF-8 treated with H2. Both types of Cu0 NPs supported on ZIF-8 were found to be active as catalysts toward the aerobic oxidation of benzyl alcohol under moderate temperature (T < 80 °C) and using air as a sustainable O2 source. Benzaldehyde yield of 66% and selectivity superior to 90% were obtained with the Cu/ZIF-8 catalyst prepared under H2 flow after 24 h under these conditions. The same material could be recycled 5 times without loss of activity, unlike the catalysts synthesized with NaBH4, as a result of the leaching of the surface copper NPs over the consecutive catalytic cycles. Finally, the most stable catalyst was successfully implemented in a tandem "one-pot" catalytic system associating benzyl alcohol oxidation and Knoevenagel condensation to synthesize benzylidene malononitrile.

Light-induced infrared difference spectroscopy on three different forms of orange carotenoid protein: focus on carotenoid vibrations.

Orange carotenoid protein (OCP) is a photoactive carotenoprotein involved in photoprotection of cyanobacteria, which uses a keto-catorenoid as a chromophore. When it absorbs blue-green light, it converts from an inactive OCPO orange form to an activated OCPR red form, the latter being able to bind the light-harvesting complexes facilitating thermal dissipation of the excess of absorbed light energy. Several research groups have focused their attention on the photoactivation mechanism, characterized by several steps, involving both carotenoid photophysics and protein conformational changes. Among the used techniques, time-resolved IR spectroscopy have the advantage of providing simultaneously information on both the chromophore and the protein, giving thereby the possibility to explore links between carotenoid dynamics and protein dynamics, leading to a better understanding of the mechanism. However, an appropriate interpretation of data requires previous assignment of marker IR bands, for both the carotenoid and the protein. To date, some assignments have concerned specific α-helices of the OCP backbone, but no specific marker band for the carotenoid was identified on solid ground. This paper provides evidence for the assignment of putative marker bands for three carotenoids bound in three different OCPs: 3'-hydroxyechineone (3'-hECN), echinenone (ECN), canthaxanthin (CAN). Light-induced FTIR difference spectra were recorded in H2O and D2O and compared with spectra of isolated carotenoids. The use of DFT calculations allowed to propose a description for the vibrations responsible of several IR bands. Interestingly, most bands are located at the same wavenumber for the three kinds of OCPs suggesting that the conformation of the three carotenoids is the same in the red and in the orange form. These results are discussed in the framework of recent time-resolved IR studies on OCP.

Synthesis of Hybrid Polyphenol/Hydroxyapatite Nanomaterials with Anti-Radical Properties.

Plant-derived natural bioactive molecules are of great therapeutic potential but, so far, their application in nanomedicine has scarcely been studied. This work aimed at comparing two methodologies, i.e., adsorption and in situ incorporation, to prepare hybrid polyphenol/hydroxyapatite nanoparticles. Two flavonoids, baicalin and its aglycone derivative baicalein, and two phenolic acids derived from caffeic acid, rosmarinic and chlorogenic acids, were studied. Adsorption of these polyphenols on pre-formed hydroxyapatite nanoparticles did not modify particle size or shape and loading was less than 10% (w/w). In contrast, presence of polyphenols during the synthesis of nanoparticles significantly impacted and sometimes fully inhibited hydroxyapatite formation but recovered particles could exhibit higher loadings. For most hybrid particles, release profiles consisted of a 24 h burst effect followed by a slow release over 2 weeks. Antioxidant properties of the polyphenols were preserved after adsorption but not when incorporated in situ. These results provide fruitful clues for the valorization of natural bioactive molecules in nanomedicine.

Baicalein-modified hydroxyapatite nanoparticles and coatings with antibacterial and antioxidant properties.

Aseptic loosening and bacterial infections are the two main causes of failure for metallic implants used for joint replacement. A coating that is both bioactive and possesses antimicrobial properties may address such shortcomings and improve the performance of the implant. We have sought to study the properties of combining hydroxyapatite-based nanoparticles or coatings with baicalein, a plant-extracted molecule with both antibacterial and antioxidant properties. (B-type) carbonated hydroxyapatite nanoparticles prepared by a chemical wet method could subsequently adsorbed by soaking in a baicalein solution. The amount of adsorbed baicalein was determined to be 63 mg.g-1 by thermogravimetric measurements. In a second approach, baicalein was adsorbed on a biomimetic calcium-deficient hydroxyapatite planar coating (12 µm thick) deposited on Ti6Al4V alloy from an aqueous solution of calcium, phosphate, sodium and magnesium salts. Soaking of the hydroxyapatite coated on titanium alloy in a baicalein solution induced partial dissolution/remodeling of the upper surface of the coating. However, the observed remodeling of the surface was much more pronounced in the presence of a baicalein solution, compared to pure water. The presence of adsorbed baicalein on the HAp layer, although it could not be precisely quantified, was assessed by XPS and fluorescence analysis. Planar coatings exhibited significant antibacterial properties against Staphylococcus epidermidis. Baicalein-modified nanoparticles exhibited significant antioxidant properties. These results illustrate the potential of hydroxyapatite used as a carrier for natural biologically-active molecules and also discuss the challenges associated with their applications as antibacterial agents.

Interactions of Calcium with Chlorogenic and Rosmarinic Acids: An Experimental and Theoretical Approach.

Chlorogenic (CA) and rosmarinic (RA) acids are two natural bioactive hydroxycinnamic acids whose antioxidant properties can be modulated by the chelation of metal ions. In this work, the interactions of these two carboxylic phenols with calcium ions and the impact of such interactions on their antioxidant activity were investigated. UV-Vis absorbance, mass spectroscopy and 1H and 13C liquid NMR were used to identify complexes formed by CA and RA with calcium. Antioxidant activities were measured by the Bois method. Density functional theory (DFT) calculations were performed to evaluate the most stable configurations and correlated with NMR data. Taken together, these data suggest that calcium ions mainly interact with the carboxylate groups of both molecules but that this interaction modifies the reactivity of the catechol groups, especially for RA. These results highlight the complex interplay between metal chelation and antioxidant properties of natural carboxylic phenols.

Small AntiMicrobial Peptide With in Vivo Activity Against Sepsis.

Antimicrobial peptides (AMPs) are considered as potential therapeutic sources of future antibiotics because of their broad-spectrum activities and alternative mechanisms of action compared to conventional antibiotics. Although AMPs present considerable advantages over conventional antibiotics, their clinical and commercial development still have some limitations, because of their potential toxicity, susceptibility to proteases, and high cost of production. To overcome these drawbacks, the use of peptides mimics is anticipated to avoid the proteolysis, while the identification of minimalist peptide sequences retaining antimicrobial activities could bring a solution for the cost issue. We describe here new polycationic ß-amino acids combining these two properties, that we used to design small dipeptides that appeared to be active against Gram-positive and Gram-negative bacteria, selective against prokaryotic versus mammalian cells, and highly stable in human plasma. Moreover, the in vivo data activity obtained in septic mice reveals that the bacterial killing effect allows the control of the infection and increases the survival rate of cecal ligature and puncture (CLP)-treated mice.

Laccase production from sucrose by recombinant Yarrowia lipolytica and its application to decolorization of environmental pollutant dyes.

Laccases are used in decolorization and biodegradation of synthetic dyes, bioremediation of industrial wastewaters and delignification of lignocellulosic compounds. The aims of the present study were the optimization of a recombinant laccase production in Yarrowia lipolytica yeast using sucrose as a main carbon source, and the application of the resulting enzyme to decolorization of synthetic dyes, which are problematic environmental pollutants. Taguchi's experimental design method was employed to optimize medium compounds. Recombinant laccase production by Y. lipolytica YL4 strain increased to 900 U L-1 after optimization of sucrose, ammonium chloride, yeast extract and thiamine levels in the modified PPB medium. Furthermore, the production rate reached 6760 U L-1 in a 5 L bioreactor which represents 4.5- and 33.5-fold increases compared to cultures that were in shake-flask with optimized and primary media, respectively. The supernatant containing secreted recombinant laccase was applied for decolorization of seven dyes. The effects of pH, the amount of enzyme and incubation period were verified. The effect of incubation time on dye decolorization by recombinant laccase was important, which has an influence of greater extent than 90% after 48 h for all dyes. The Trametes versicolor laccase can be efficiently produced in Y. lipolytica and the recombinant enzyme has a considerable potential in the decolorization of pollutant synthetic dyes.

Production of Laccase by Recombinant Yarrowia lipolytica from Molasses: Bioprocess Development Using Statistical Modeling and Increase Productivity in Shake-Flask and Bioreactor Cultures.

Laccases are used in numerous applications, from green degradation of various xenobiotic compounds, waste detoxification, textile dye bleaching, and delignification of lignocellulose materials to biofuel production. In this study, the recombinant Yarrowia lipolytica YL4 strain carrying the white-rot fungus Trametes versicolor laccase IIIb gene was used for laccase production from beet molasses as an agro-industrial residue. Response surface methodology was used to statistical optimization of the production of laccase by Y. lipolytica using an industrial medium containing molasses which allows a six times increase in laccase activity compared to primary medium contains glucose after 144 h. In bioreactor cultivation after 48 h, laccase production reached to 3.7- and 22.5-fold more than optimized and primary media in shake-flask cultures, respectively. Laccase productivity in bioreactor (0.0937 U/h) was higher than shake-flask culture (0.0084 U/h). The present study provides valuable information about statistical optimization of bioprocess development for cost-effective production of laccase and other heterologous proteins in Y. lipolytica from beet molasses as sole carbon source, thus allowing the valorization and decreasing environmental pollution of this agro-industrial waste.

C2 Arylated Benzo[b]thiophene Derivatives as Staphylococcus aureus NorA Efflux Pump Inhibitors.

An innovative and straightforward synthesis of second-generation 2-arylbenzo[b]thiophenes as structural analogues of INF55 and the first generation of our laboratory-made molecules was developed. The synthesis of C2-arylated benzo[b]thiophene derivatives was achieved through a method involving direct arylation, followed by simple structural modifications. Among the 34 compounds tested, two of them were potent NorA pump inhibitors, which led to a 16-fold decrease in the ciprofloxacin minimum inhibitory concentration (MIC) against the SA-1199B strain at concentrations of 0.25 and 0.5 µg mL(-1) (1 and 1.5 µm, respectively). This is a promising result relative to that obtained for reserpine (MIC=20 µg mL(-1)), a reference compound amongst NorA pump inhibitors. These molecules thus represent promising candidates to be used in combination with ciprofloxacin against fluoroquinolone-resistant strains.

Oxidation of laccase for improved cathode biofuel cell performances.

Graphite rods were modified by substituted aryldiazonium salts allowing subsequent laccase immobilisation and direct electron transfer at the cathode. Two covalent enzyme immobilisation methods were performed with carboxy and amino substituted grafted groups, either via the formation of an amide bond or a Schiff base between the glycosidic groups of the enzyme and the amino groups on the electrode surface, respectively. Laccase adsorption efficiency was consistently compared to the covalent attachment method on the same carbon surface, showing that the latter method led to a higher immobilisation yield when the electrode surface was functionalised with carboxylic groups, as shown from both laccase activity measurement towards an organic reducing substrate, ABTS, and quantitative XPS analysis. Both analytical methods led to similar laccase surface coverage estimations. From activity measurements, when laccase was covalently immobilised on the electrode functionalised with carboxylic groups, the surface coverage was found to be 43 ± 2% whereas it was only 10 ± 3% when laccase was adsorbed. Biocatalysed dioxygen reduction current was also higher in the case of covalent immobilisation. For the first time, oxidised laccase performances were compared to unmodified laccase, showing significant improved efficiency when using oxidised laccase: the current obtained with oxidised laccase was 141 ± 37 µA cm(-2) compared to 28 ± 6 µA cm(-2) for unmodified laccase after covalent immobilisation of the enzyme on a graphite electrode functionalised with carboxylic groups.

Boronic species as promising inhibitors of the Staphylococcus aureus NorA efflux pump: study of 6-substituted pyridine-3-boronic acid derivatives.

In response to the extensive use of antibiotics, bacteria have evolved numerous mechanisms of defense against antimicrobial agents. Among them, extrusion of the antimicrobial agents outside the bacterial cell through efflux pumps is a major cause of concern. At first limited to one or few structurally-related antibiotics, bacterial resistance have then progressed towards cross-resistance between different classes of antibiotics, leading to multidrug-resistant microorganisms. Emergence of these pathogens requires development of novel therapeutic strategies and inhibition of efflux pumps appears to be a promising strategy that could restore the potency of existing antibiotics. NorA is the most studied chromosomal efflux pump of Staphylococcus aureus; it is known to be implied in resistance of Methicillin-resistant S. aureus (MRSA) strains against a wide range of unrelated substrates, including hydrophilic fluoroquinolones. Starting from 6-benzyloxypyridine-3-boronic acid I that we previously identified as a potential inhibitor of the NorA efflux pump against the NorA-overexpressing S. aureus 1199B strain (SA1199B), we describe here the synthesis and biological evaluation of a series of 6-(aryl)alkoxypyridine-3-boronic acids. 6-(3-Phenylpropoxy)pyridine-3-boronic acid 3i and 6-(4-phenylbutoxy)pyridine-3-boronic acid 3j were found to potentiate ciprofloxacin activity by a 4-fold increase compared to the parent compound I. In addition, it has been shown that both compounds promote Ethidium Bromide (EtBr) accumulation in SA1199B, thus corroborating their potential mode of action as NorA inhibitors.

Novel synthetic bis-indolic derivatives with antistaphylococcal activity, including against MRSA and VISA strains.

OBJECTIVES: We report the synthesis, antibacterial activity and toxicity of 24 bis-indolic derivatives obtained during the development of new ways of synthesis of marine bis-indole alkaloids from the spongotine, topsentin and hamacanthin classes. METHODS: Innovative ways of synthesis and further structural optimizations led to bis-indoles presenting either the 1-(1H-indol-3'-yl)-1,2-diaminoethane unit or the 1-(1H-indol-3-yl)ethanamine unit. MIC determination was performed for reference and clinical strains of Staphylococcus aureus and CoNS species. MBC, time-kill kinetics, solubility, hydrophobicity index, plasma protein-binding and cytotoxicity assays were performed for lead compounds. Inhibition of the S. aureus NorA efflux pump was also tested for bis-indoles with no antistaphylococcal activity. RESULTS: Lead compounds were active against both S. aureus and CoNS species, with MICs between 1 and 4 mg/L. Importantly, the same MICs were found for MRSA and vancomycin-intermediate S. aureus strains. Early concentration-dependent bactericidal activity was observed for lead derivatives. Compounds with no intrinsic antibacterial activity could inhibit the S. aureus NorA efflux pump, which is involved in resistance to fluoroquinolones. At 0.5 mg/L, the most effective compound led to an 8-fold reduction of the ciprofloxacin MIC for the SA-1199B S. aureus strain, which overexpresses NorA. However, the bis-indole compounds displayed a high hydrophobicity index and high plasma protein binding, which significantly reduced antibacterial activity. CONCLUSIONS: We have synthesized and characterized novel bis-indole derivatives as promising candidates for the development of new antistaphylococcal treatments, with preserved activity against MDR S. aureus strains.

Combating against methicillin-resistant Staphylococcus aureus - two fatty acids from Purslane (Portulaca oleracea†L.) exhibit synergistic effects with erythromycin.

OBJECTIVES: The aims of this study were to identify the active ingredients from Portulaca oleracea L. (PO) that could provide synergism with antibiotics against methicillin-resistant Staphylococcus aureus (MRSA) and their possible mechanisms of resistance inhibition. METHODS: High-speed counter-current chromatography (HSCCC) coupled with gas chromatography-mass spectrometry and a panel of laboratory MRSA strains were used for checkerboard and efflux inhibitory assays. KEY FINDINGS: Linoleic and oleic acids were identified from HSCCC fraction 18 of PO with synergistic antibacterial activity when combined with erythromycin against RN4220/pUL5054. Ethidium bromide efflux inhibitory studies revealed that linoleic and oleic acids may interfere the activity of MsrA pump. By comparing among a panel of linoleic and oleic acids analogues, unsaturated fatty acids in salt form with cis configuration and an increase in number of double bonds were found to further increase the antibacterial activity when used alone or in combination with antibiotics. CONCLUSION: This study reported for the first time that two active ingredients, namely linoleic and oleic acids, were identified from PO with synergistic antibacterial activity when combined with erythromycin against MRSA RN4220/pUL5054 and possibly act by inhibiting the efflux pumps of the bacteria cells.

Using planktonic microorganisms to supply the unpurified multi-copper oxidases laccase and copper efflux oxidases at a biofuel cell cathode.

The feasibility to apply crude culture supernatants that contain the multicopper oxidases laccase or copper efflux oxidase (CueO) as oxygen reducing catalysts in a biofuel cell cathode is shown. As enzyme-secreting recombinant planktonic microorganisms, the yeast Yarrowia lipolytica and the bacterium Escherichia coli were investigated. The cultivation and operation conditions (choice of medium, pH) had distinct effects on the electro-catalytic performance. The highest current density of 119 ± 23 µA cm(-2) at 0.400 V vs. NHE was obtained with the crude culture supernatant of E. coli cells overexpressing CueO and tested at pH 5.0. In comparison, at pH 7.4 the electrode potential at 100 µA cm(-2) is 0.25 V lower. Laccase-containing supernatants of Y. lipolytica yielded a maximum current density of 6.7 ± 0.4 µAcm(-2) at 0.644 V vs. NHE. These results open future possibilities to circumvent elaborate enzyme purification procedures and realize cost effective and easy-to-operate enzymatic biofuel cells.

1-(1H-indol-3-yl)ethanamine derivatives as potent Staphylococcus aureus NorA efflux pump inhibitors.

The synthesis of 37 1-(1H-indol-3-yl)ethanamine derivatives, including 12 new compounds, was achieved through a series of simple and efficient chemical modifications. These indole derivatives displayed modest or no intrinsic anti-staphylococcal activity. By contrast, several of the compounds restored, in a concentration-dependent manner, the antibacterial activity of ciprofloxacin against Staphylococcus aureus strains that were resistant to fluoroquinolones due to overexpression of the NorA efflux pump. Structure-activity relationships studies revealed that the indolic aldonitrones halogenated at position 5 of the indole core were the most efficient inhibitors of the S. aureus NorA efflux pump. Among the compounds, (Z)-N-benzylidene-2-(tert-butoxycarbonylamino)-1-(5-iodo-1H-indol-3-yl)ethanamine oxide led to a fourfold decrease of the ciprofloxacin minimum inhibitory concentration against the SA-1199B strain when used at a concentration of 0.5 mg L(-1) . To the best of our knowledge, this activity is the highest reported to date for an indolic NorA inhibitor. In addition, a new antibacterial compound, tert-butyl (2-(3-hydroxyureido)-2-(1H-indol-3-yl)ethyl)carbamate, which is not toxic for human cells, was also found.

First identification of boronic species as novel potential inhibitors of the Staphylococcus aureus NorA efflux pump.

Overexpression of efflux pumps is an important mechanism of bacterial resistance that results in the extrusion of antimicrobial agents outside the bacterial cell. Inhibition of such pumps appears to be a promising strategy that could restore the potency of existing antibiotics. The NorA efflux pump of Staphylococcus aureus confers resistance to a wide range of unrelated substrates, such as hydrophilic fluoroquinolones, leading to a multidrug-resistance phenotype. In this work, approximately 150 heterocyclic boronic species were evaluated for their activity against susceptible and resistant strains of S. aureus. Twenty-four hit compounds, although inactive when tested alone, were found to potentiate ciprofloxacin activity by a 4-fold increase at concentrations ranging from 0.5 to 8 µg/mL against S. aureus 1199B, which overexpresses NorA. Boron-free analogues showed no biological activity, thus revealing that the boron atom is crucial for biological activity. This work describes the first reported efflux pump inhibitory activity of boronic acid derivatives.

Concerted electron/proton transfer mechanism in the oxidation of phenols by laccase.

This study aimed to assess structural requirements in the enzyme/substrate interactions that are responsible for tuning the enzymatic reactivity. To better assess the role of the aspartic residue in the substrate-binding pocket of basidiomycete-type laccases, we compared the catalytic efficiency of wild-type enzymes to that of a mutant in which carboxylic acid residue Asp206 was changed to alanine. Oxidation efficiency towards phenolic substrates by laccases of Trametes villosa, Trametes versicolor and a T. versicolor D206A mutant was studied at two pH values. By the Hammett approach and Marcus analysis, we obtained unambiguous evidence that the oxidation takes place by a concerted electron/proton transfer (EPT) mechanism, and that at pH 5 (optimum pH for enzyme activity) the phenolic proton is transferred to Asp206 during the concerted electron/proton transfer process.

Tuning the antibacterial activity of amphiphilic neamine derivatives and comparison to paromamine homologues.

Aminoglycosides are antibiotic drugs that act through binding to rRNA. In the search for antimicrobial amphiphilic aminoglycosides targeting bacterial membranes, we report here on the discovery of three dialkyl derivatives of the small aminoglycoside neamine active against susceptible and resistant Gram-positive and Gram-negative bacteria. One of these derivatives (R = 2-naphthylpropyl), which has good activity against MRSA and VRSA, showed a low toxicity in eukaryotic cells at 10 µM. The synthesis of amphiphilic paromamine and neamine homologous derivatives pointed out the role of the 6'-amine function of the neamine core in the antibacterial effects. The optimal number of lipophilic substituents to be attached to the neamine core and the corresponding required lipophilicity determined here should permit a more selective targeting of bacterial membranes relative to eukaryotic membranes. This work revealed the existence of windows of lipophilicity necessary for obtaining strong antibacterial effects that should be of interest in the field of antibacterial amphiphilic aminoglycosides.

Overcoming bottlenecks of enzymatic biofuel cell cathodes: crude fungal culture supernatant can help to extend lifetime and reduce cost.

Enzymatic biofuel cells (BFCs) show great potential for the direct conversion of biochemically stored energy from renewable biomass resources into electricity. However, enzyme purification is time-consuming and expensive. Furthermore, the long-term use of enzymatic BFCs is hindered by enzyme degradation, which limits their lifetime to only a few weeks. We show, for the first time, that crude culture supernatant from enzyme-secreting microorganisms (Trametes versicolor) can be used without further treatment to supply the enzyme laccase to the cathode of a mediatorless BFC. Polarization curves show that there is no significant difference in the cathode performance when using crude supernatant that contains laccase compared to purified laccase in culture medium or buffer solution. Furthermore, we demonstrate that the oxygen reduction activity of this enzymatic cathode can be sustained over a period of at least 120 days by periodic resupply of crude culture supernatant. This is more than five times longer than control cathodes without the resupply of culture supernatant. During the operation period of 120 days, no progressive loss of potential is observed, which suggests that significantly longer lifetimes than shown in this work may be possible. Our results demonstrate the possibility to establish simple, cost efficient, and mediatorless enzymatic BFC cathodes that do not require expensive enzyme purification procedures. Furthermore, they show the feasibility of an enzymatic BFC with an extended lifetime, in which self-replicating microorganisms provide the electrode with catalytically active enzymes in a continuous or periodic manner.