The Performance of a Modified Anode Using a Combination of Kaolin and Graphite Nanoparticles in Microbial Fuel Cells.

The bacterial anode in microbial fuel cells was modified by increasing the biofilm's adhesion to the anode material using kaolin and graphite nanoparticles. The MFCs were inoculated with G. sulfurreducens, kaolin (12.5 g·L-1), and three different concentrations of graphite (0.25, 1.25, and 2.5 g·L-1). The modified anode with the graphite nanoparticles (1.25 g·L-1) showed the highest electroactivity and biofilm viability. A potential of 0.59, 0.45, and 0.23 V and a power density of 0.54 W·m-2, 0.3 W·m-2, and 0.2 W·m-2 were obtained by the MFCs based on kaolin-graphite nanoparticles, kaolin, and bare anodes, respectively. The kaolin-graphite anode exhibited the highest Coulombic efficiency (21%) compared with the kaolin (17%) and the bare (14%) anodes. Scanning electron microscopy and confocal laser scanning microscopy revealed a large amount of biofilm on the kaolin-graphite anode. We assume that the graphite nanoparticles increased the charge transfer between the bacteria that are in the biofilm and are far from the anode material. The addition of kaolin and graphite nanoparticles increased the attachment of several bacteria. Thus, for MFCs that are fed with wastewater, the modified anode should be prepared with a pure culture of G. sulfurreducens before adding wastewater that includes non-exoelectrogenic bacteria.

Anode amendment with kaolin and activated carbon increases electricity generation in a microbial fuel cell.

The bacterial anode is a key factor for microbial fuel cell (MFC) performance. This study examined the potential of kaolin (fine clay) to enhance bacteria and conductive particle attachment to the anode. The bio-electroactivity of MFCs based on a carbon-cloth anode modified by immobilization with kaolin, activated carbon, and Geobacter sulfurreducens (kaolin-AC), with only kaolin (kaolin), and a bare carbon-cloth (control) anodes were examined. When the MFCs were fed with wastewater, the MFCs based on the kaolin-AC, kaolin, and bare anodes produced a maximum voltage of 0.6 V, 0.4 V, and 0.25 V, respectively. The maximum power density obtained by the MFC based on the kaolin-AC anode was 1112 mW‧m-2 at a current density of 3.33 A‧m-2, 12% and 56% higher than the kaolin and the bare anodes, respectively. The highest Coulombic efficiency was obtained by the kaolin-AC anode (16%). The relative microbial diversity showed that Geobacter displayed the highest relative distribution of 64% in the biofilm of the kaolin-AC anode. This result proved the advantage of preserving the bacterial anode exoelectrogens using kaolin. To our knowledge, this is the first study evaluating kaolin as a natural adhesive for immobilizing exoelectrogenic bacteria to anode material in MFCs.

Effects of Atmospheric Plasma Corona Discharge on Saccharomyces cerevisiae: Viability, Permeability, and Morphology.

Food spoilage is a routine challenge in food production. Saccharomyces cerevisiae is a major contaminating microorganism associated with fruit pulps and juices. Our study demonstrated the effect of a plasma corona discharge on S. cerevisiae viability, membrane permeability, and morphology when the cells were prepared in both dry and wet modes. The S. cerevisiae viability was examined as a function of the duration of plasma exposure, the sample's distance from the treating head, initial cell concentration, and yeast suspension volume. The results showed a linear correlation between the exposure duration and the CFU/mL in both dry and wet modes. When the initial yeast concentration was 106 CFU/mL, complete eradication in the dry and wet modes occurred after 45 and 240 s, respectively. Exposure of different initial concentrations of S. cerevisiae to plasma in dry (20 s) or wet (90 s) mode led to 2 to 3 orders of magnitude reduction. In both modes, there was total eradication when the initial cell concentration was about 103 CFU/mL. The cell-membrane permeability was examined using a flow cytometer and the fluorescent dye propidium iodide (PI). Plasma treatment in the dry mode for 30 and 45 s led to 51% and 76% PI-positive cells. Similar results were obtained in the wet mode but with a longer exposure for 120 and 240 s, respectively. Atmospheric plasma may provide disinfection technology for the food industry in a short process without heating.

Hydrogen Production in Microbial Electrolysis Cells Based on Bacterial Anodes Encapsulated in a Small Bioreactor Platform.

Microbial electrolysis cells (MECs) are an emerging technology capable of harvesting part of the potential chemical energy in organic compounds while producing hydrogen. One of the main obstacles in MECs is the bacterial anode, which usually contains mixed cultures. Non-exoelectrogens can act as a physical barrier by settling on the anode surface and displacing the exoelectrogenic microorganisms. Those non-exoelectrogens can also compete with the exoelectrogenic microorganisms for nutrients and reduce hydrogen production. In addition, the bacterial anode needs to withstand the shear and friction forces existing in domestic wastewater plants. In this study, a bacterial anode was encapsulated by a microfiltration membrane. The novel encapsulation technology is based on a small bioreactor platform (SBP) recently developed for achieving successful bioaugmentation in wastewater treatment plants. The 3D capsule (2.5 cm in length, 0.8 cm in diameter) physically separates the exoelectrogenic biofilm on the carbon cloth anode material from the natural microorganisms in the wastewater, while enabling the diffusion of nutrients through the capsule membrane. MECs based on the SBP anode (MEC-SBPs) and the MECs based on a nonencapsulated anode (MEC control) were fed with Geobacter medium supplied with acetate for 32 days, and then with artificial wastewater for another 46 days. The electrochemical activity, chemical oxygen demand (COD), bacterial anode viability and relative distribution on the MEC-SBP anode were compared with the MEC control. When the MECs were fed with artificial wastewater, the MEC-SBP produced (at -0.6 V) 1.70 ± 0.22 A m-2, twice that of the MEC control. The hydrogen evolution rates were 0.017 and 0.005 m3 m-3 day-1, respectively. The COD consumption rate for both was about the same at 650 ± 70 mg L-1. We assume that developing the encapsulated bacterial anode using the SBP technology will help overcome the problem of contamination by non-exoelectrogenic bacteria, as well as the shear and friction forces in wastewater plants.

Extracellular proteolytic activation of Pseudomonas aeruginosa aminopeptidase (PaAP) and insight into the role of its non-catalytic N-terminal domain.

Pseudomonas aeruginosa secretes several endopeptidases, including elastase, alkaline proteinase (Apr), a lysine-specific endopeptidase (LysC), and an aminopeptidase (PaAP), all of which are important virulence factors. Activation of the endopeptidases requires removal of an inhibitory N-terminal propeptide. Activation of pro-PaAP, in contrast, requires C-terminal processing. The activating proteases of pro-PaAP and their cleavage site(s) have not yet been defined. Studying pro-PaAP processing in a wild type P. aeruginosa strain and strains lacking either elastase or both elastase and Apr, we detected three processing variants, each ~56 kDa in size (AP56). Activity assays and N- and C-terminal sequence analyses of these variants pointed at LysC as the principal activating protease, cleaving a Lys512-Ala513 peptide bond at the C-terminal end of pro-PaAP. Elastase and/or Apr are required for activation of LysC, suggesting both are indirectly involved in activation of PaAP. To shed light on the function(s) of the N-terminal domain of AP56, we purified recombinant AP56 and generated from it the 28 kDa catalytic domain (AP28). The kinetic constants (Km and Kcat) for hydrolysis of Leu-, Lys-, Arg- and Met-p-nitroanilide (pNA) derivatives by AP56 and AP28 were then determined. The catalytic coefficients (Kcat/Km) for hydrolysis of all four substrates by AP28 and AP56 were comparable, indicating that the non-catalytic domain is not involved in hydrolysis of small substrates. It may, however, regulate hydrolysis of natural peptides/proteins. Lys-pNA was hydrolyzed 2 to 3-fold more rapidly than Leu-pNA and ~8-fold faster than Arg- or Met-pNA, indicating that Lys-pNA was the preferred substrate.

Resuscitation of Pulsed Electric Field-Treated Staphylococcus aureus and Pseudomonas putida in a Rich Nutrient Medium.

Pulsed electric fields (PEFs) technology was reported to be useful as a disinfection method in the liquid food industry. This technology may lead to membrane permeabilization and bacterial death. However, resuscitation of viable but non-culturable cells and sublethally injured microorganisms in food was reported to be associated with foodborne outbreaks. The main aim of this study was to investigate the possible recovery of injured PEF-treated bacteria. The PEF treatment of Staphylococcus aureus and Pseudomonas putida led to a reduction of 3.2 log10 and 4.8 log10, respectively. After 5 h, no colony forming units (CFUs) were observed when the bacteria were suspended in phosphate buffer saline (PBS); and for 24 h, no recovery was observed. The PEF-treated S. aureus in brain-heart infusion (BHI) medium were maintained at 1.84 × 104 CFU mL-1 for about 1.5 h. While P. putida decreased to zero CFU mL-1 by the 4th hour. However, after that, both bacteria recovered and began to multiply. Flow cytometry analysis showed that PEF treatment led to significant membrane permeabilization. Mass spectrometry analysis of PEF-treated P. putida which were suspended in BHI revealed over-expression of 22 proteins, where 55% were related to stress conditions. Understanding the recovery conditions of PEF-treated bacteria is particularly important in food industry pasteurization. To our knowledge, this is the first comprehensive study describing the recovery of injured PEF-treated S. aureus and P. putida bacteria.

Metal-Organic Polymer-Derived Interconnected Fe-Ni Alloy by Carbon Nanotubes as an Advanced Design of Urea Oxidation Catalysts.

The electrochemical urea oxidation reaction (UOR) is considered as a promising renewable source for harvesting energy from waste. We report a new synthetic design approach to produce an iron-nickel alloy nanocatalyst from a metal-organic polymer (MOP) by a single-step carbonization process at 500 °C, thus forming a core-shell of iron-nickel-coated carbon (C@FeNi) nanostructures wired by embedded carbon nanotubes (CNTs) (CNT/C@FeNi). Powder X-ray diffraction confirmed the formation of metallic FeNi3 alloy nanoparticles (∼20 to 28 nm). Our experimental results showed that MOP containing CNTs acquired an interconnected hierarchical topology, which prevented the collapse of its microstructure during pyrolysis. Hence, CNT/C@FeNi shows higher porosity (10 times) than C@FeNi. The electrochemical UOR in alkaline electrolytes on these catalysts was studied using cyclic voltammetry (CV). The result showed a higher anodic current (3.5 mA cm-2) for CNT/C@FeNi than for C@FeNi (1.1 mA cm-2) at 1.5 V/RHE. CNT/C@FeNi displayed good stability in chronoamperometry experiments and a lower Tafel slope (33 mV dec-1) than C@FeNi (41.1 mV dec-1). In this study, CNT/C@FeNi exhibits higher exchange current density (3.2 µA cm-2) than does C@FeNi (2 µA cm-2). The reaction rate orders of CNT/C@FeNi and C@FeNi at a kinetically controlled potential of 1.4 V/RHE were 0.5 and 0.9, respectively, higher than the 0.26 of ß-Ni(OH)2, Ni/Ni(OH)2 electrodes. The electrochemical impedance result showed a lower charge-transfer resistance for CNT/C@FeNi (61 Ω·cm-2) than for C@FeNi (162 Ω·cm-2), due to faster oxidation kinetics associated with the CNT linkage. Moreover, CNT/C@FeNi exhibited a lower Tafel slope and resistance and higher heterogeneity (25.2 × 10-5 cm s-1), as well as relatively high faradic efficiency (68.4%) compared to C@FeNi (56%). Thus, the carbon-coated FeNi3 core connected by CNT facilitates lower charge-transfer resistance and reduces the UOR overpotential.

Effects of Atmospheric Plasma Corona Discharge on Agrobacterium tumefaciens Survival.

Soil-borne pathogenic microorganisms are known to cause extensive crop losses. Agrobacterium tumefaciens, a member of the Proteobacteria, causes the neoplastic crown gall disease in plants. Plant protection is mainly based on toxic chemicals that are harmful to the environment. The use of cold atmospheric-pressure plasma is an attractive method for microbial eradication. Its antimicrobial mechanism includes the formation of large quantities of reactive oxygen species (ROS). The advantages of eradicating bacteria using cold plasma are not needed for chemicals, short treatment, and environmental temperatures. This study examined the impact of plasma corona discharge exposure on A. tumefaciens viability, membrane permeability, relative cell size, and ROS formation. The results showed that 90 s of plasma exposure led to a reduction by four orders of magnitude when the initial concentration was 1 × 107 CFU/mL and in a dry environment. When the initial concentration was 1 × 106 CFU/mL, 45 s of exposure resulted in total bacterial eradication. In a liquid environment, in an initial concentration of 2.02 × 106 CFU/mL, there was no complete bacterial eradication even at the most prolonged examined exposure (90 s). The influence of plasma treatment on the membrane permeability of A. tumefaciens, and their possible recovery, were analyzed using flow cytometer analysis using propidium iodide (PI). When the plasma-treated bacteria were suspended in Luria-Bertani (LB) (rich medium), the PI-positive count of the plasma-treated bacteria after two hours was 12 ± 3.9%. At the 24th hour, this percentage was only 1.74 ± 0.6%, as the control (0.7 ± 0.1%). These results may indicate the repair of the plasma-treated bacteria that were suspended in LB. At the 24th hour, the relative cell size of the treated bacteria shifted to the right, to ~3 × 104 forward side scatter (FSC), about 0.5-fold higher than the untreated cells. Measurement of the ROS showed that the intracellular fluorescence of the 90-s plasma-treated cells led to significant fluorescence formation of 32 relative fluorescence units (RFU)/cell (9 × 104 fold, compared to the nontreated cells). This study showed that cold plasma is a useful method for A. tumefaciens eradication. The eradication mechanism involves ROS generation, membrane permeability, and changes in cell size.

Eradication of Saccharomyces cerevisiae by Pulsed Electric Field Treatments.

One of the promising technologies that can inactivate microorganisms without heat is pulsed electric field (PEF) treatment. The aim of this study was to examine the influence of PEF treatment (2.9 kV cm-1, 100 Hz, 5000 pulses in trains mode of 500 pulses with a pulse duration of 10 µs) on Saccharomyces cerevisiae eradication and resealing in different conditions, such as current density (which is influenced by the medium conductivity), the sort of medium (phosphate buffered saline (PBS) vs. yeast malt broth (YMB) and a combined treatment of PEF with the addition of preservatives. When the S. cerevisiae were suspended in PBS, increasing the current density from 0.02 to 3.3 A cm-2 (corresponding to a total specific energy of 22.04 to 614.59 kJ kg-1) led to an increase of S. cerevisiae eradication. At 3.3 A cm-2, a total S. cerevisiae eradication was observed. However, when the S. cerevisiae in PBS was treated with the highest current density of 3.3 A cm-2, followed by dilution in a rich YMB medium, a phenomenon of cell membrane resealing was observed by flow cytometry (FCM) and CFU analysis. The viability of S. cerevisiae was also examined when the culture was exposed to repeating PEF treatments (up to four cycles) with and without the addition of preservatives. This experiment was performed when the S. cerevisiae were suspended in YMB containing tartaric acid (pH 3.4) and ethanol to a final concentration of 10% (v/v), which mimics wine. It was shown that one PEF treatment cycle led to a reduction of 1.35 log10, compared to 2.24 log10 when four cycles were applied. However, no synergic effect was observed when the preservatives, free SO2, and sorbic acid were added. This study shows the important and necessary knowledge about yeast eradication and membrane recovery processes after PEF treatment, in particular for application in the liquid food industry.

Effects of Atmospheric Plasma Corona Discharges on Soil Bacteria Viability.

Crop contamination by soil-borne pathogenic microorganisms often leads to serious infection outbreaks. Plant protection requires disinfection of agricultural lands. The chemical and the physical disinfection procedures have several disadvantages, including an irreversible change in the soil ecosystem. Plasma, the "fourth state of matter" is defined as an ionized gas containing an equal number of negatively and positively charged particles. Cold-plasma technology with air or oxygen as the working gas generates reactive oxygen species, which are found to efficiently eradicate bacteria. In this study, we examined the effect of atmospheric plasma corona discharges on soil bacteria viability. Soil that was exposed to plasma for 60 s resulted in bacterial reduction by two orders of magnitude, from 1.1 × 105 to 2.3 × 103 cells g-1 soil. Exposure for a longer period of 5 min did not lead to further significant reduction in bacterial concentration (a final reduction of only 2.5 orders of magnitude). The bacterial viability was evaluated using a colorimetric assay based on the bacterial hydrogenases immediately after exposure and at selected times during 24 h. The result showed no recovery in the bacterial viability. Plasma discharged directly on bacteria that were isolated from the soil resulted in a reduction by four orders of magnitude in the bacterial concentration compared to untreated isolated bacteria: 2.6 × 10-3 and 1.7 × 10-7, respectively. The plasma-resistant bacteria were found to be related to the taxonomic phylum Firmicutes (98.5%) and comprised the taxonomic orders Bacillales (95%) and Clostridiales (2%). To our knowledge, this is the first study of soil bacteria eradication using plasma corona discharges.

Erratum: Farber, R.; Rosenberg, A.; Rozenfeld, S.; Banet, G.; Cahan, R. Bioremediation of Artificial Diesel-Contaminated Soil Using Bacterial Consortium Immobilized to Plasma-Pretreated Wood Waste. Microorganisms 2019, 7, 497.

The authors wish to make the following erratum in this paper [...].

Bioremediation of Artificial Diesel-Contaminated Soil Using Bacterial Consortium Immobilized to Plasma-Pretreated Wood Waste.

Bioaugmentation is a bioremediation option based on increasing the natural in-situ microbial population that possesses the ability to degrade the contaminating pollutant. In this study, a diesel-degrading consortium was obtained from an oil-contaminated soil. The diesel-degrading consortium was grown on wood waste that was plasma-pretreated. This plasma treatment led to an increase of bacterial attachment and diesel degradation rates. On the 7th day the biofilm viability on the plasma-treated wood waste reached 0.53 ± 0.02 OD 540 nm, compared to the non-treated wood waste which was only 0.34 ± 0.02. Biofilm attached to plasma-treated and untreated wood waste which was inoculated into artificially diesel-contaminated soil (0.15% g/g) achieved a degradation rate of 9.3 mg day-1 and 7.8 mg day-1, respectively. While, in the soil that was inoculated with planktonic bacteria, degradation was only 5.7 mg day-1. Exposing the soil sample to high temperature (50 °C) or to different soil acidity did not influence the degradation rate of the biofilm attached to the plasma-treated wood waste. The two most abundant bacterial distributions at the family level were Xanthomonadaceae and Sphingomonadaceae. To our knowledge, this is the first study that showed the advantages of biofilm attached to plasma-pretreated wood waste for diesel biodegradation in soil.

Influence of the current density in moderate pulsed electric fields on P. putida F1 eradication.

Eradication of P. putida F1 was investigated as a function of current density in pulsed electric fields of 6.7, 4, 2.8, 2 and 1 kV/cm. The pulse numbers were 200, 2000, 5000 and 10,000 and were performed by a series of trains of 500 pulses (except for the 200 pulses). The frequency was 100 Hz and pulse durations were 10 µs or 20 µs as indicated for each experiment. The current density range was 0.02 ±â€¯0.01 to 5.2 ±â€¯0.5 Acm-2. A clear tendency for increasing bacterial death was found as a result of increasing the current density in each of the tested electric field strengths. The total bacterial eradication when the electric field was reduced from 4 to 1 kV/cm was obtained at a higher current density, 2 ±â€¯0.2 and 5.2 ±â€¯0.5 Acm-2, respectively. Increasing the current density led to higher cell permeability and larger bacteria size. The percentage of propidium iodide permeability in an electric field of 1 kV/cm at a current density of 5.2 ±â€¯0.5 Acm-2 was 65 ±â€¯0.3% compared to the control that was only 10 ±â€¯0.9%. The cell size at 1 kV/cm in a current density of 5.2 ±â€¯0.5 Acm-2 was about 3-fold higher compared to untreated cells. To the best of our knowledge, this is the first study that evaluated the influence of increasing current density on bacterial eradication in moderate electric fields.

Exfoliated molybdenum di-sulfide (MoS2) electrode for hydrogen production in microbial electrolysis cell.

The most widely reported catalyst in microbial electrochemical cells (MEC) cathodes is platinum (Pt). The disadvantages of Pt include its high cost and sensitivity to various molecules. In this research an exfoliated molybdenum di-sulfide (MoS2-EF) catalyst was synthesized. The size of the obtained particles was 200 ±â€¯50 nm, 50-fold smaller than the pristine MoS2 catalyst. The MoS2-EF Raman spectrum displays the E12g and A1g peaks at 373 cm-1 and 399 cm-1. Electrochemical characterization by linear sweep voltammetry (LSV) of a rotating disc electrode RDE showed that the current density of Pt in 0.5 M H2SO4 was 3.3 times higher than MoS2-EF. However, in phosphate buffer (pH-7) electrolyte this ratio diminished to 1.9. The polarization curve of Pt, MoS2-EF and the pristine MoS2 electrodes, at -1.3 V in MEC configuration in abiotic conditions exhibit current densities of 17.46, 12.67 and 3.09 mA cm-2, respectively. Hydrogen evolution rates in the same MEC with a Geobacter sulfurreducens anode and Pt, MoS2-EF and the pristine MoS2 cathodes were 0.106, 0.133 and 0.083 m3 d-1 m-3, respectively. The results in this study show that MoS2-EF led to highly purified hydrogen and that this catalyst can serve as an electrochemical active and cost-effective alternative to Pt.

Proteomic Assessment of the Expression of Genes Related to Toluene Catabolism and Porin Synthesis in Pseudomonas stutzeri ST-9.

The organization and expression of Pseudomonas stutzeri ST-9 genes related to toluene catabolism and porin synthesis was investigated. Toluene-degrading genes were found to be localized in the chromosome close to a phage-type integrase. A regulatory gene and 21 genes related to an aromatics degradation pathway are organized as a putative operon. These proteins are upregulated in the presence of toluene. Fourteen outer membrane proteins were identified as porins in the ST-9 genome. The identified porins showed that the main detected porins are related to the OmpA and OprD superfamilies. The percentage of porins in the outer membrane protein fraction, as determined by mass spectrometry, was 73% and 54% when the cells were cultured with toluene and with glucose, respectively. Upregulation of OmpA and downregulation of OprD occurred in the presence of toluene. A porin fraction (90% OprD) from both cultures was isolated and examined as a toluene uptake system using the liposome-swelling assay. Liposomes were prepared with the porin fraction from a culture that was grown on toluene (T-proteoliposome) or glucose (G-proteoliposome). There was no significant difference in the permeability rate of the different solutes through the T-proteoliposome and the G-proteoliposome.

Effect of toluene on Pseudomonas stutzeri ST-9 morphology - plasmolysis, cell size, and formation of outer membrane vesicles.

Isolated toluene-degrading Pseudomonas stutzeri ST-9 bacteria were grown in a minimal medium containing toluene (100 mg·L(-1)) (MMT) or glucose (MMG) as the sole carbon source, with specific growth rates of 0.019 h(-1) and 0.042 h(-1), respectively. Scanning (SEM) as well as transmission (TEM) electron microscope analyses showed that the bacterial cells grown to mid-log phase in the presence of toluene possess a plasmolysis space. TEM analysis revealed that bacterial cells that were grown in MMT were surrounded by an additional "material" with small vesicles in between. Membrane integrity was analyzed by leakage of 260 nm absorbing material and demonstrated only 7% and 8% leakage from cultures grown in MMT compared with MMG. X-ray microanalysis showed a 4.3-fold increase in Mg and a 3-fold increase in P in cells grown in MMT compared with cells grown in MMG. Fluorescence-activated cell sorting (FACS) analysis indicated that the permeability of the membrane to propidium iodide was 12.6% and 19.6% when the cultures were grown in MMG and MMT, respectively. The bacterial cell length increased by 8.5% ± 0.1% and 17% ± 2%, as measured using SEM images and FACS analysis, respectively. The results obtained in this research show that the presence of toluene led to morphology changes, such as plasmolysis, cell size, and formation of outer membrane vesicles. However, it does not cause significant damage to membrane integrity.

Draft Genome Sequence of the Toluene-Degrading Pseudomonas stutzeri Strain ST-9.

Strain ST-9 was isolated from toluene-contaminated soil (Samaria, Israel). The draft genome has an estimated size of 4.8 Mb, exhibits an average G+C content of 60.37%, and is predicted to encode 4,183 proteins, including a gene cluster for aromatic hydrocarbon degradation. It is assigned to genomovar 3 of Pseudomonas stutzeri.

Conjugated and immobilized photosensitizers for combating bacterial infections.

The technique of photosensitization for eradication of bacterial cells involves the use of molecules called photosesitizers (PSs) which generate reactive oxygen species (ROS) upon illumination with light of a suitable wavelength. ROS can oxidize biological molecules such as proteins, nucleic acids and lipids, which ultimately leads to bacterial cell death. Use of PS-conjugates and immobilized PS can lead to a reduction in the amount of a compound necessary for bacterial cell eradication. In addition, PS-conjugates for delivering photosensitizer molecules are more effective for clinical applications, since the photosensitizers are targeted directly to bacterial cells. This review reports studies and patents that demonstrate the possibility of increasing bacterial cells eradication by using specific and non-specific PS-conjugates such as: PS-antibiotic, PS-polycation (including PS-poly-L-lysine and PS-polyethyleneimine), PS-bacteriophage, PS-IgG and PS-siderophore. Studies and patents describing immobilized PS for drug delivery are also considered.

Current production in a microbial fuel cell using a pure culture of Cupriavidus basilensis growing in acetate or phenol as a carbon source.

A microbial fuel cell (MFC) was operated with a pure culture of Cupriavidus basilensis bacterial cells growing in the anode compartment in a defined medium containing acetate or phenol. Operating this mediator-less MFC under a constant external resistor of 1 kΩ with acetate or phenol led to current generation of 902 and 310 mA m(-2) respectively. In the MFC which was operated using acetate or phenol, the current density measured from the plankton bacterial cells with a fresh electrode was 125 and 109 mA m(-2), respectively, whereas the current obtained with biofilm-covered electrodes in sterile medium was 541 and 228 mA m(-2) respectively. After 72 h in the MFC, 86% of the initial phenol concentration was removed, while only 64% was removed after the same time in the control MFC which was held at an open circuit potential (OCP). Furthermore, SEM and confocal microscopy analyses demonstrated a developed biofilm with a live C. basilensis population. In conclusion, in this study we demonstrated, for the first time, use of C. basilensis facultative aerobe bacterial cells in a MFC using acetate or phenol as the sole carbon source which led to electricity generation.

Effect of external voltage on Pseudomonas putida F1 in a bio electrochemical cell using toluene as sole carbon and energy source.

A bio electrochemical cell (BEC) was constructed as a typical two-chamber microbial fuel cell (MFC), except that it was operated under external voltage instead of constant resistance as in an MFC. The anode chamber contained a pure culture of Pseudomonas putida F1 grown in a minimal medium containing toluene as the sole carbon and energy source. Operating the BEC under external voltages of 75, 125, 175, 250 and 500 mV (versus an Ag/AgCl reference electrode) led to increased bacterial cell growth to an OD(600) of 0.62-0.75, while the control BEC, which was not connected to external voltage, reached an OD(600) of only 0.3. Examination of the current generated under external voltages of 75, 125, 175, 250 and 500 mV showed that the maximal currents were 11, 23, 28, 54 and 94 mA m(-2), respectively. Cyclic voltammetry experiments demonstrated an anodic peak at 270 mV, which may imply oxidation of a vital molecule. The average residual toluene concentration after 147 h in the BEC operated under external voltage was 22 %, whereas in the control BEC it was 81 %. Proteome analysis of bacterial cells grown in the BEC (125 mV) revealed two groups of proteins, which are ascribed to charge transfer in the bacterial cells and from the cell to the electrode. In conclusion, operating the BEC at 75-500 mV enabled growth of a pure culture of P. putida F1 and toluene degradation even in an oxygen-limited environment.