Enabling anoxic acetate assimilation by electrode-driven respiration in the obligate aerobe, Pseudomonas putida.

This study examined the obligate aerobe, Pseudomonas putida, using acetate as the sole carbon and energy source, and respiration via an anode as the terminal electron acceptor under anoxic conditions. P. putida showed significantly different acetate assimilation in a closed-circuit microbial fuel cell (CC-MFC) compared to an open circuit MFC (OC-MFC). More than 72% (2.6 mmol) of acetate was consumed during 84 hrs in the CC-MFC in contrast to the no acetate consumption observed in the OC-MFC. The CC-MFC produced 150 µA (87 C) from acetate metabolization. Electrode-based respiration reduced the NADH/NAD+ ratio anaerobically, which is similar to the aerobic condition. The CC-MFC showed significantly higher acetyl-CoA synthetase activity than the OC-MFC (0.028 vs. 0.001 µmol/min/mg), which was comparable to the aerobic condition (circa 60%). Overall, electrode-based respiration enables P. putida to metabolize acetate under anoxic conditions and provide a platform to regulate the bacterial redox balance without oxygen.

Supply of proton enhances CO electrosynthesis for acetate and volatile fatty acid productions.

The microbial electrosynthesis is a platform to supply protons and electrons to improve the conversion efficiency and production rate for the valorization of C1 gas. This study examined proton migration and electron transfer of the electrode and microbe by using various external parameters in the electrosynthesis of CO. The CO electrosynthesis achieved almost double of coulombic efficiency than the conventional CO2 electrosynthesis. The maximum volumetric acetate production rate was 0.71 g/L/day in the BES, which was 2-6 times higher than reported elsewhere. These results show that the efficient proton migration and electron transfer can enhance the productivity and conversion efficiency of the biological CO conversion in a bioelectrochemical system.

Small Current but Highly Productive Synthesis of 1,3-Propanediol from Glycerol by an Electrode-Driven Metabolic Shift in Klebsiella pneumoniae L17.

Electrofermentation actively regulates the bacterial redox state, which is essential for bioconversion and has been highlighted as an effective method for further improvements of the productivity of either reduced or oxidized platform chemicals. 1,3-Propanediol (1,3-PDO) is an industrial value-added chemical that can be produced from glycerol fermentation. The bioconversion of 1,3-PDO from glycerol requires additional reducing energy under anoxic conditions. The cathode-based conversion of glycerol to 1,3-PDO with various electron shuttles (2-hydroxy-1,4-naphthoquinone, neutral red, and hydroquinone) using Klebsiella pneumoniae L17 was investigated. The externally poised potential of -0.9 V vs. Ag/AgCl to the cathode increased 1,3-PDO (35.5±3.1 mm) production if 100 µm neutral red was used compared with non-bioelectrochemical system fermentation (23.7±2.4 mm). Stoichiometric metabolic flux and transcriptional analysis indicated a shift in the carbon flux toward the glycerol reductive pathway. The homologous overexpression of glycerol dehydratase (DhaB) and 1,3-PDO oxidoreductase (DhaT) enzymes synergistically enhanced 1,3-PDO conversion (39.3±0.8 mm) under cathode-driven fermentation. Interestingly, a small current uptake (0.23 mmol of electrons) caused significant metabolic flux changes with a concomitant increase in 1,3-PDO production. This suggests that both an increase in 1,3-PDO production and regulation of the cellular metabolic pathway are feasible by electrode-driven control in cathodic electrofermentation.

Metabolic shift of Klebsiella pneumoniae L17 by electrode-based electron transfer using glycerol in a microbial fuel cell.

Klebsiella pneumoniae is used widely for the production of value-added chemicals from glycerol, and is known as an exoelectrogen with an externally provided electron shuttle. In this study, the metabolic shift in K. pneumoniae L17 by the activation of electrode-based respiration was examined using microbial fuel cells (MFCs). The mRNA expression levels of the related enzymes for glycerol conversion were compared under electrode-driven anaerobic respirational conditions (i.e., MFC) and fermentative conditions (i.e., non-MFC). mRNA expression clearly responded to the electrode-based electron transfer with simultaneous current generation and changes in metabolite production. The NAD+-dependent pathways were activated and more acetate (21.7 vs. 14.6 mM), 3-HP (7.6 vs. 5.3 mM) and 1,3-PDO (45.5 vs. 38.1 mM) and less ethanol production were observed under MFC conditions than under non-MFC (39.6 vs 66.7 mM). Stoichiometric metabolic flux analysis was examined in MFC condition. These results suggest that electron excretion to the carbon electrode drives the metabolic pathway shift of K. pneumoniae L17, and can provide an active control strategy for the fermentative pathway of glycerol.

Recent developments and key barriers to advanced biofuels: A short review.

Biofuels are regarded as one of the most viable options for reduction of CO2 emissions in the transport sector. However, conventional plant-based biofuels (e.g., biodiesel, bioethanol)'s share of total transportation-fuel consumption in 2016 was very low, about 4%, due to several major limitations including shortage of raw materials, low CO2 mitigation effect, blending wall, and poor cost competitiveness. Advanced biofuels such as drop-in, microalgal, and electro biofuels, especially from inedible biomass, are considered to be a promising solution to the problem of how to cope with the growing biofuel demand. In this paper, recent developments in oxy-free hydrocarbon conversion via catalytic deoxygenation reactions, the selection of and lipid-content enhancement of oleaginous microalgae, electrochemical biofuel conversion, and the diversification of valuable products from biomass and intermediates are reviewed. The challenges and prospects for future development of eco-friendly and economically advanced biofuel production processes also are outlined herein.

Spontaneous and applied potential driven indium recovery on carbon electrode and crystallization using a bioelectrochemical system.

Indium removal and recovery on a carbon electrode under a microbial fuel cell (MFC)-based oxidation/reduction reaction were examined using synthetic wastewater. More than 90% of In3+ ions were removed after continuous operation of the MFC for 14 days with an average current generation of ∼50 µA. During operation, indium particulates formed on the cathode carbon electrode. Scanning electron microscopy equipped with X-ray energy dispersive spectroscopy showed that they were composed of amorphous and crystalline indium hydroxides (In(OH)3 and In(OH)·H2O). When the current flow was reversed to drive the oxidation of the particles to recover the indium from indium hydroxides, a few indium oxide (In2O3) nanocrystals with a rectangular platelet shape formed on the electrode, while the majority of the amorphous and crystalline indium hydroxides re-dissolved into the aqueous environment. Overall, these results demonstrate a feasible route towards the MFC-based recovery of indium with the simultaneous generation of bioelectricity.

Co-culture-based biological carbon monoxide conversion by Citrobacter amalonaticus Y19 and Sporomusa ovata via a reducing-equivalent transfer mediator.

The biological conversion of carbon monoxide (CO) has been highlighted for the development of a C1 gas biorefinery process. Despite this, the toxicity and low reducing equivalent of CO uptake make biological conversion difficult. The use of synthetic co-cultures is an alternative way of enhancing the performance of CO bioconversion. This study evaluated a synthetic co-culture consisting of Citrobacter amalonaticus Y19 and Sporomusa ovata for acetate production from CO. In this consortium, the CO2 and H2 produced by the water-gas shift reaction of C. amalonaticus Y19, were utilized further by S. ovata. Higher acetate production was achieved in the co-culture system compared to the monoculture counterparts. Furthermore, syntrophic cooperation via various reducing equivalent carriers provided new insights into the synergistic metabolic benefits with a toxic and refractory substrate, such as CO. This study also suggests an appropriate model for examining the syntrophic interaction between microbial species in a mixed community.

A Study on Growth Performance of Ducks Fed Diets with Different Types of Sipjeondaebo-Tang Byproduct Meal and Red Ginseng Marc with Fermented Red Koji and Ammonia Fluxes in Duck Litter using Alum or Aluminum Chloride.

The aims of the present study were to investigate the growth performance of ducks fed diets with different types of Sipjeondaebo-tang (ST) byproduct meal and red ginseng marc with fermented red koji (RGMK), and to investigate ammonia (NH3) fluxes from duck litter treated with alum or aluminum chloride (AlCl3). A total of 270 1-d-old ducks (180 males and 90 females) were allotted in a completely randomized design with 6 treatments and 3 replicates of 15 birds per pen. The six diet treatments were: basal diet, pelleted 1% ST byproduct powder, pelleted 1% RGMK, 1% blends (a mixture of ST byproduct and RGMK) powder, 1% pelleted blends, and coated pellets of 1% blends. The six litter treatments with 6 diet treatments were: no treatment, 50, 100, or 200 g alum/kg duck litter, and 100 g or 200 g AlCl3/kg duck litter (treatments T1, T2, T3, T4, and T5, respectively). During days 10 to 40, ducks fed the 5 experimental diets had significantly different (p<0.05) weight gains and feed conversion ratios compared with those fed the control diet, but initial body weight, final body weight, feed intake, and mortality were not affected. There were significant differences (p<0.05) in NH3 fluxes among treatments over the 6 weeks of the study, except for week 0. The relative NH3 losses at week 6 were lower by 25.6, 45.3, 45.6, 46.7, and 48.6% than those in the controls in T1, T2, T3, T4, and T5 respectively. In conclusion, feeding pellets or coated pellets of ST and RGMK and using alum or AlCl3 in the litter at the same time improves weight gain and feed conversion ratio performance and reduces mortality and NH3 losses in ducks.

Electrochemically enhanced microbial CO conversion to volatile fatty acids using neutral red as an electron mediator.

Conversion of C1 gas feedstock, including carbon monoxide (CO), into useful platform chemicals has attracted considerable interest in industrial biotechnology. Nevertheless, the low conversion yield and/or growth rate of CO-utilizing microbes make it difficult to develop a C1 gas biorefinery process. The Wood-Ljungdahl pathway which utilize CO is a pathway suffered from insufficient electron supply, in which the conversion can be increased further when an additional electron source like carbohydrate or hydrogen is provided. In this study, electrode-based electron transference using a bioelectrochemical system (BES) was examined to compensate for the insufficient reducing equivalent and increase the production of volatile fatty acids. The BES including neutral red (BES-NR), which facilitated electron transfer between bacteria and electrode, was compared with BES without neutral red and open circuit control. The coulombic efficiency based on the current input to the system and the electrons recovered into VFAs, was significantly higher in BES-NR than the control. These results suggest that the carbon electrode provides a platform to regulate the redox balance for improving the bioconversion of CO, and amending the conventional C1 gas fermentation.

Anodic electro-fermentation of 3-hydroxypropionic acid from glycerol by recombinant Klebsiella pneumoniae L17 in a bioelectrochemical system.

BACKGROUND: 3-Hydroxypropionic acid (3-HP) is an important platform chemical which can be produced biologically from glycerol. Klebsiella pneumoniae is an ideal biocatalyst for 3-HP because it can grow well on glycerol and naturally synthesize the essential coenzyme B12. On the other hand, if higher yields and titers of 3-HP are to be achieved, the sustained regeneration of NAD+ under anaerobic conditions, where coenzyme B12 is synthesized sustainably, is required. RESULTS: In this study, recombinant K. pneumoniae L17 overexpressing aldehyde dehydrogenase (AldH) was developed and cultured in a bioelectrochemical system (BES) with the application of an electrical potential to the anode using a chronoamperometric method (+0.5 V vs. Ag/AgCl). The BES operation resulted in 1.7-fold enhancement of 3-HP production compared to the control without the applied potential. The intracellular NADH/NAD+ ratio was significantly lower when the L17 cells were grown under an electric potential. The interaction between the electrode and overexpressed AldH was enhanced by electron shuttling mediated by HNQ (2-hydroxy-1,4-naphthoquinone). CONCLUSIONS: Enhanced 3-HP production by the BES was achieved using recombinant K. pneumoniae L17. The quinone-based electron transference between the electrode and L17 was investigated by respiratory uncoupler experiments. This study provides a novel strategy to control the intracellular redox states to enhance the yield and titer of 3-HP production as well as other bioconversion processes.

Polymer Film-Based Screening and Isolation of Polylactic Acid (PLA)-Degrading Microorganisms.

Polylactic acid (PLA) has been highlighted as an alternative renewable polymer for the replacement of petroleum-based plastic materials, and is considered to be biodegradable. On the other hand, the biodegradation of PLA by terminal degraders, such as microorganisms, requires a lengthy period in the natural environment, and its mechanism is not completely understood. PLA biodegradation studies have been conducted using mainly undefined mixed cultures, but only a few bacterial strains have been isolated and examined. For further characterization of PLA biodegradation, in this study, the PLA-degrading bacteria from digester sludge were isolated and identified using a polymer film-based screening method. The enrichment of sludge on PLA granules was conducted with the serial transference of a subculture into fresh media for 40 days, and the attached biofilm was inoculated on a PLA film on an agar plate. 3D optical microscopy showed that the isolates physically degraded the PLA film due to bacterial degradation. 16S rRNA gene sequencing identified the microbial colonies to be Pseudomonas sp. MYK1 and Bacillus sp. MYK2. The two isolates exhibited significantly higher specific gas production rates from PLA biodegradation compared with that of the initial sludge inoculum.

Glycerol-fed microbial fuel cell with a co-culture of Shewanella oneidensis MR-1 and Klebsiella pneumonae J2B.

Glycerol is an attractive feedstock for bioenergy and bioconversion processes but its use in microbial fuel cells (MFCs) for electrical energy recovery has not been investigated extensively. This study compared the glycerol uptake and electricity generation of a co-culture of Shewanella oneidensis MR-1 and Klebsiella pneumonia J2B in a MFC with that of a single species inoculated counterpart. Glycerol was metabolized successfully in the co-culture MFC (MFC-J&M) with simultaneous electricity production but it was not utilized in the MR-1 only MFC (MFC-M). A current density of 10 mA/m(2) was obtained while acidic byproducts (lactate and acetate) were consumed in the co-culture MFC, whereas they are accumulated in the J2B-only MFC (MFC-J). MR-1 was distributed mainly on the electrode in MFC-J&M, whereas most of the J2B was observed in the suspension in the MFC-J reactor, indicating that the co-culture of both strains provides an ecological driving force for glycerol utilization using the electrode as an electron acceptor. This suggests that a co-culture MFC can be applied to electrical energy recovery from glycerol, which was previously known as a refractory substrate in a bioelectrochemical system.

Effect of graphene on growth of neuroblastoma cells.

The unique properties of graphene have earned much interest in the fields of materials science and condensed-matter physics in recent years. However, the biological applications of graphene remain largely unexplored. In this study, we investigated the conditions and viability of a cell culture exposed to graphene onto glass and SiO2/Si, using a human nerve cell line, SH-SY5Y. Cell viability was 84% when cultured on glass and SiO2/Si coated with graphene as compared with culturing on polystyrene surface. Fluorescence data showed that the presence of graphene did not influence cell morphology. These findings suggest that graphene may be used for biological applications.

Protective effect of maghemite nanoparticles on ultraviolet-induced photo-damage in human skin fibroblasts.

This study examined the optical properties of an oxidized form of maghemite (γ-Fe(2)O(3)) nanoparticles and their protective effects against the photoaging of human skin fibroblasts irradiated with ultraviolet (UV) light. Nanoparticles with diameters ranging from 8.7 to 12 nm were prepared using a chemical co-precipitation method. The nanoparticles were coated with two surfactants to obtain a water-based product. The onset of the absorption of the γ-Fe(2)O(3) nanoparticles in the UV-visible absorption spectra increased with increasing particle size. The γ-Fe(2)O(3) nanoparticles significantly inhibited the production of matrix metalloproteinase-1 in human skin fibroblast HS 68 cells by 60% compared with the UV-irradiated control. These results suggest that γ-Fe(2)O(3) nanoparticles have photoprotective properties, and have potential use as an agent against photoaging.