Complete genome sequence of Methanothermobacter sp. DP, a hydrogenotrophic and thermophilic methanogen

Here, we report the complete genome sequence of the thermophilic hydrogenotrophic methanogen Methanothermobacter sp. DP isolated in South Korea from an anaerobic digester fed with cigarette waste. The genome consists of 1,693,285 bp, with 1,772 protein-coding genes and a GC content of 48.8%.

Anisotropic Alignment of Bacterial Nanocellulose Ionogels for Unconventionally High Combination of Stiffness and Damping

Ionogels are emerging materials for advanced electrochemical devices; however, their mechanical instability to external stresses has raised concerns about their safety. This study reports aligned bacterial nanocellulose (BC) ionogel films swelled with the model ionic liquid (IL) of 1-ethyl-3-methylimidazolium tetrafluoroborate (EMImBF₄) for an unprecedented combination of high stiffness and high energy dissipation without significant loss of ionic conductivity. The aligned BC ionogel films are prepared through wet-state stretching methods, followed by drying and swelling by ILs. The aligned ionogel films exhibit significantly improved dynamic mechanical properties, overcoming the mechanical conventional limit of traditional materials by 2.0 times at 25 °C and by a maximum of 4.0 times at 0 °C. Additionally, the same samples exhibit relatively high ionic conductivities of 0.16 mS cm^-1 at 20 °C and 0.45 mS cm^-1 at 60 °C with storage moduli over 10 GPa. The synergistic effect of the mechanical reinforcements by alignment of the BC nanofibers and the plasticizing effects by ILs could be attributed to the significant enhancement of dynamic mechanical properties and the retention of ionic conductivities. These results will lead to a deeper understanding of the material design for mechanically superior ionogel systems with increasing demands for advanced electronic and electrochemical devices.

Chain elongation process for caproate production using lactate as electron donor in Megasphaera hexanoica

Megasphaera hexnaoica is anaerobic bacteria who has well running reverse β-oxidation pathway. In previous study, the strain showed excellent production of medium chain carboxylic acids (MCCAs) using fructose as electron donor. In this study, chain elongation process study using lactate instead of fructose was conducted in M. hexnaoica fermentation. It was found that M. hexanoica can use lactate as electron donor in chain elongation process. 8.9 g/L caproate production was achieved in fermentation using lactate as sole electron donor. Compare to fructose condition, lactate as electron donor showed more than 3 times higher specific titer and specific productivity. In addition, when fructose and lactate were used as electron donor simultaneously, further improvement of MCCAs production was observed to achieve maximum caproate productivity of 20.9 g/L/day. Utilization of lactate as electron donor in M. hexanoica showed potential opportunity in chain elongation process.

Production of microalgae with high lipid content and their potential as sources of nutraceuticals

In the current global scenario, the world is under a serious dilemma due to the increasing human population, industrialization, and urbanization. The ever-increasing need for fuels and increasing nutritional problems have made a serious concern on the demand for nutrients and renewable and eco-friendly fuel sources. Currently, the use of fossil fuels is creating ecological and economic problems. Microalgae have been considered as a promising candidate for high-value metabolites and alternative renewable energy sources. Microalgae offer several advantages such as rapid growth rate, efficient land utilization, carbon dioxide sequestration, ability to cultivate in wastewater, and most importantly, they do not participate in the food crop versus energy crop dilemma or debate. An efficient microalgal biorefinery system for the production of lipids and subsequent byproduct for nutraceutical applications could well satisfy the need. But, the current microalgal cultivation systems for the production of lipids and nutraceuticals do not offer techno-economic feasibility together with energy and environmental sustainability. This review article has its main focus on the production of lipids and nutraceuticals from microalgae, covering the current strategies used for lipid production and the major high-value metabolites from microalgae and their nutraceutical importance. This review also provides insights on the future strategies for enhanced microalgal lipid production and subsequent utilization of microalgal biomass.

GRAPHICAL ABSTRACT

Electronic wastes: A near inexhaustible and an unimaginably wealthy resource for water splitting electrocatalysts

E-wastes comprise complex combinations of potentially toxic elements that cause detrimental effects of the environmental contamination; besides their posing threat, most of the products also contain valuable and recoverable materials (Li, Au, Ag, W, Se, Te, etc.), which make them distinct from other forms of industrial wastes. Most of these value-added elements which are primarily employed in electronic goods are disposed of by incineration and land-filling. This is a serious issue besides just environmental pollution, as IUPAC recognized that such ignorance of or poor attention to e-waste recycling has put several elements in the periodic table to the list of endangered elements. Recycling these wastes utilized for electrocatalytic water splitting to produce H₂. These recovered e-wastes materials are used as electrocatalysts for the water-splitting, additives to enhance reaction kinetics, and substrate electrodes as well. Recycling and recovery of value-added materials in the view of applying them to electrocatalytic water splitting with endangered elements' perspective have not been covered by any recent review so far. Hence, this review is dedicated to discussing the opportunities available with recycling e-wastes, types of value-added materials that can be recovered for water splitting, strategies exploited, and prospects are discussed in details.

Metabolic cascade of complex organic wastes to medium-chain carboxylic acids: A review on the state-of-the-art multi-omics analysis for anaerobic chain elongation pathways

Medium-chain carboxylic acid (MCCA) production from organic wastes has attracted much attention because of their higher energy contents and diverse applications. Anaerobic reactor microbiomes are stable and resilient and have resulted in efficient performance during many years of operation for thousands of full-scale anaerobic digesters worldwide. The method underlying how the relevant microbial pathways contribute to elongate carbon chains in reactor microbiomes is important. In particular, the reverse β-oxidation pathway genes are critical to upgrading short-chain fermentation products to MCCAs via a chain elongation (CE) process. Diverse genomics and metagenomics studies have been conducted in various fields, ranging from intracellular metabolic pathways to metabolic cascades between different strains. This review covers taxonomic approach to culture processes depending on types of organic wastes and the deeper understanding of genome and metagenome-scale CE pathway construction, and the co-culture and multi-omics technology that should be addressed in future research.

Mass cultivation and harvesting of microalgal biomass: Current trends and future perspectives

Microalgae are unicellular photosynthetic organisms capable of producing high-value metabolites like carbohydrates, lipids, proteins, polyunsaturated fatty acids, vitamins, pigments, and other high-value metabolites. Microalgal biomass gained more interest for the production of nutraceuticals, pharmaceuticals, therapeutics, food supplements, feed, biofuel, bio-fertilizers, etc. due to its high lipid and other high-value metabolite content. Microalgal biomass has the potential to convert trapped solar energy to organic materials and potential metabolites of nutraceutical and industrial interest. They have higher efficiency to fix carbon dioxide (CO₂) and subsequently convert it into biomass and compounds of potential interest. However, to make microalgae a potential industrial candidate, cost-effective cultivation systems and harvesting methods for increasing biomass yield and reducing the cost of downstream processing have become extremely urgent and important. In this review, the current development in different microalgal cultivation systems and harvesting methods has been discussed.

Characterisation of bacterial nanocellulose and nanostructured carbon produced from crude glycerol by Komagataeibacter sucrofermentans

Bacterial nanocellulose (BNC), which has tunable properties, is a precursor of nanostructured energy storage materials; however, the cost of BNC production is challenging. This study uses crude glycerol from the biodiesel industry as a carbon nutrient and first-time carbonised BNC from K. sucrofermentans that is applied in energy storage. From crude glycerol in static cultivation, 6.4 g L^-1 BNC was produced with a high crystallinity index (85%) and tensile properties in comparison to conventionally used pure carbon substrates. Carbon materials were derived from the BNC retained fibrous and crystalline features with disordered porous structures. The electrochemical properties of the carbon materials have a specific capacitance of 140 F g^-1. This study highlights the valorisation of waste glycerol from the biodiesel industry as a substrate for efficient BNC production and the energy storage potential of carbon derived from BNC as renewable energy materials.

Complete Genome Sequence of Methanothermobacter sp. Strain THM-1, a Thermophilic and Hydrogenotrophic Methanogen Isolated from an Anaerobic Reactor in South Korea

Methanothermobacter sp. strain THM-1, a thermophilic and hydrogenotrophic methanogen, was isolated from an anaerobic reactor enriched with thermophilic methanogens. The genome of THM-1 shares 98.81% of its sequence with Methanothermobacter wolfeii isolate SIV6 and consists of 1,724,502 bp with 1,665 protein-coding genes, 50 noncoding RNAs, and a GC content of 48.6%.

Anaerobic co-digestion of bioplastics as a sustainable mode of waste management with improved energy production - A review

The world of bioplastics has expanded rapidly in recent decades, and the new waste stream generated is creating major barriers to waste processing. Anaerobic co-digestion is to be considered one of the best options for the efficient processing of bioplastic waste due to its minimal space requirements, lower degrees of environmental pollution, and renewable energy generation. The higher carbon to nitrogen (C/N) ratio of bioplastics poses a challenge to anaerobic digestion, but co-digestion with lower C/N ratio biowastes can efficiently degrade bioplastics and improve biogas production in the system. In the future, the collection of organic waste in biodegradable plastic bags makes the waste management process easier for anaerobic digestion plants. The present review paper discusses current trends of bioplastic usage, degradation strategies, and the potential of anaerobic co-digestion for waste management with improved energy production in anaerobic digesters.

Pretreatment strategies for enhanced biogas production from lignocellulosic biomass

The inclusion of a pretreatment step in anaerobic digestion processes increases the digestibility of lignocellulosic biomass and enhances biogas yields by promoting lignin removal and the destruction of complex biomass structures. The increase in surface area enables the efficient interaction of microbes or enzymes, and a reduction in cellulose crystallinity improves the digestion process under anaerobic conditions. The pretreatment methods may vary based on the type of the lignocellulosic biomass, the nature of the subsequent process and the overall economics of the process. An improved biogas production by 1200% had been reported when ionic liquid used as pretreatment strategy for anaerobic digestion. The different pretreatment techniques used for lignocellulosic biomasses are generally grouped into physical, chemical, physicochemical, and biological methods. These four modes of pretreatment on lignocellulosic biomass and their impact on biogas production process is the major focus of this review article.

Impact of feedstocks and downstream processing technologies on the economics of caproic acid production in fermentation by Megasphaera elsdenii T81

Caproic acid (CA) was produced by Megasphaera elsdenii T81 with Jerusalem artichoke tubers (JA) as a feedstock. More CA was produced under the medium with the acid hydrolysate of JA than the comparative medium with a carbon composition similar to that of JA. CA was produced up to 13.0 g/L and 0.52 g/L/h with extractive fermentation using a mixed solvent of alamine 336 in oleyl alcohol at 37 °C. The JA cost to produce 1 ton of CA is only 505 USD, which is much lower than that required for purchasing sucrose (860 USD) in CA production. As a result of the analysis performed using SuperPro Designer, including the cost of distillation to obtain pure CA, the estimated production cost for CA from dry JA is 1869 USD/ton CA at the production scale of 2000 ton/year, which is lower than the current market price for petroleum-derived CA (~2500 USD/ton).

Simultaneous production of methane and acetate by thermophilic mixed culture from carbon dioxide in bioelectrochemical system

A thermophilic bioelectrochemical system was operated with mixed culture at 60 °C, while introducing only carbon dioxide. Methane production was initially observed in a membrane-less single chamber without a mediator, but eventually acetate was also found as 10.5 g/L after 137 days of operation. Comparing the microbial communities before and after the electricity supply using next-generation sequencing technology, acetoclastic methanogens such as Methanosaeta concilii were increased, and this result also indicates the production of acetate in bioelectrochemical CO₂ conversion system. With the advent of sulfate-reducing bacteria, Desulfotomaculum peckii was considered to be an acetate production promoter. These high production results for both methane and acetate can be applied to CO₂ storage using excess electricity for value-added chemicals.

Electrochemical behaviors of Li-argyrodite-based all-solid-state batteries under deep-freezing conditions

We probe the electrochemical performance of Li-argyrodite-based all-solid-state batteries under deep-freezing conditions (-30 °C) using electrochemical impedance spectroscopy. The performance deterioration is mainly caused by the increased interfacial resistances of electrolyte and active materials resulting from the slow kinetics of Li-ion transport in solid materials at low temperatures.

New coculture system of Clostridium spp. and Megasphaera hexanoica using submerged hollow-fiber membrane bioreactors for caproic acid production

In this study, a coculture bioprocess was developed with Clostridium strains producing butyric acid and Megasphaera hexanoica producing caproic acid from the butyric acid. The two bacterial strains were each cultivated in two submerged hollow-fiber membrane bioreactors (s-HF/MBRs), separately. Each fermentation broth was filtered through the membrane modules, and the filtered broth was either interchanged on another reactor or obtained sequentially through. Using s-HF/MBRs, the caproic acid concentration increased to 10.08 g L^-1, with the fastest productivity of 0.69 g L^-1 h^-1, which higher than that previously reported.

Quantitative Analysis of Microstructures and Reaction Interfaces on Composite Cathodes in All-Solid-State Batteries Using a Three-Dimensional Reconstruction Technique

The composite cathode of an all-solid-state battery composed of various solid-state components requires a dense microstructure and a highly percolated solid-state interface different from that of a conventional liquid-electrolyte-based Li-ion battery. Indeed, the preparation of such a system is particularly challenging. In this study, quantitative analyses of composite cathodes by three-dimensional reconstruction analysis were performed beyond the existing qualitative analysis, and their microstructures and reaction interfaces were successfully analyzed. Interestingly, various quantitative values of structure properties (such as the volume ratio, connectivity, tortuosity, and pore formation) associated with material optimization and process development were predicted, and they were found to result in limited electrochemical charge/discharge performances. We also verified that the effective two-phase boundaries were significantly suppressed to ∼23% of the total volume because of component dispersion and packing issues.

Enhanced extraction of butyric acid under high-pressure CO2 conditions to integrate chemical catalysis for value-added chemicals and biofuels

BACKGROUND

Extractive fermentation with the removal of carboxylic acid requires low pH conditions because acids are better partitioned into the solvent phase at low pH values. However, this requirement conflicts with the optimal near-neutral pH conditions for microbial growth.

RESULTS

CO2 pressurization was used, instead of the addition of chemicals, to decrease pH for the extraction of butyric acid, a fermentation product of Clostridium tyrobutyricum, and butyl butyrate was selected as an extractant. CO2 pressurization (50 bar) improved the extraction efficiency of butyric acid from a solution at pH 6, yielding a distribution coefficient (D) 0.42. In situ removal of butyric acid during fermentation increased the production of butyric acid by up to 4.10 g/L h, an almost twofold increase over control without the use of an extraction process.

CONCLUSION

In situ extraction of butyric acid using temporal CO2 pressurization may be applied to an integrated downstream catalytic process for upgrading butyric acid to value-added chemicals in an organic solvent.

Optimization of hexanoic acid production in recombinant Escherichia coli by precise flux rebalancing

The aim of this study is to demonstrate that rebalancing of metabolic fluxes at acetyl-CoA branch node can substantially improve the titer and productivity of hexanoic acid in recombinant Escherichia coli strains. First, a hexanoic acid-producing E. coli strain was constructed by expressing genes encoding β-ketothiolase (BktB) from Cupriavidus necator and acetyl-CoA transferase (ACT) from Megasphaera sp. MH in a butyric acid producer strain. Next, metabolic flux was optimized at the acetyl-CoA branch node by fine-tuning the expression level of the gene for acetyl-CoA acetyltransferase (AtoB). Four synthetic 5'-untranslated regions were designed for atoB using UTR Designer to modulate the expression level of the gene. Notably, the productivity of the optimized strain (14.7 mg/L/h) was the highest among recombinant E. coli strains in literature when using a similar inoculum size for fermentation. These results show that fine-tuning the expression level of atoB is critical for production of hexanoic acid.

Collateral hydrogenation over proton-conducting Ni/BaZr0.85Y0.15O3−δ catalysts for promoting CO2 methanation

Despite the importance of CO₂ methanation for eco-friendly carbon-neutral fuel recycling, the current technologies, relying on catalytic hydrogenation over metal-based catalysts, face technological and economical limitations. Herein, we employ the steam hydrogenation capability of proton conductors to achieve collateral CO₂ methanation over the Ni/BaZr_0.85Y_0.15O_3−δ catalyst, which is shown to outperform its conventional Ni/Al₂O₃ counterpart in terms of CH₄ yield (8% higher) and long-term stability (3% higher for 150 h) at 400 °C while exhibiting a CH₄ selectivity above 98%. Moreover, infrared and X-ray photoelectron spectroscopy analyses reveal the appearance of distinct mobile proton-related OH bands during the methanation reaction.

A novel steam hydrogenation process is demonstrated by applying collateral CO₂ methanation over Ni/BaZr_0.85Y_0.15O_3−δ, which outperforms its conventional Ni/Al₂O₃ counterpart.

A Hierarchically Modified Graphite Cathode with Au Nanoislands, Cysteamine, and Au Nanocolloids for Increased Electricity-Assisted Production of Isobutanol by Engineered Shewanella oneidensis MR-1

It is necessary to understand the surface structural effects of electrodes on the bioalcohol productivity of Shewanella oneidensis MR-1, but this research area has not been deeply explored. Here, we report that the electricity-assisted isobutanol productivity of Shewanella oneidensis MR-1::pJL23 can be enhanced by sequentially modifying a graphite felt (GF) surface with Au nanoislands (Au), cysteamine (NH₂), and Au nanoparticles (Au NPs). After bacteria were incubated for 50 h with the unmodified GF under various electrode potentials (vs Ag/AgCl), the bacterial isobutanol concentrations increased from 2.9 ± 1 mg/L under no electricity supply to a maximum of 5.9 ± 1 mg/L at -0.6 V. At this optimum electrode potential, the concentrations continued increasing to 9.1 ± 1, 14 ± 2, and 27 ± 2 mg/L when the GF electrodes were modified with Au, NH₂-Au, and Au NP-NH₂-Au, respectively. We further studied how each surface structure affected the bacterial adsorptions, current profiles, and biofilms' electrochemical performances. In particular, these modifications induced the adsorption of elongated bacteria, with the amount dependent on the electrode structure. In the presence of electric supply, the amount of elongated bacteria further increased. We also found that the NH₂-Au-GF and Au NP-NH₂-Au-GF electrodes themselves could increase the concentrations to 11 ± 0.3 and 12 ± 2 mg/L, respectively, upon the bacterial incubation without electricity. Among the electrodes tested, the contribution of electricity to the bacterial isobutanol production was the greatest with the Au NP-NH₂-Au-GF electrode. After 96 h of incubation, the concentration increased to 72 ± 2 mg/L, which was 4.7 and 3.7 times the previously reported values obtained without and with electricity, respectively.

Silica formation with nanofiber morphology via helical display of the silaffin R5 peptide on a filamentous bacteriophage

Biological systems often generate unique and useful structures, which can have industrial relevance either as direct components or as an inspiration for biomimetic materials. For fabrication of nanoscale silica structures, we explored the use of the silaffin R5 peptide from Cylindrotheca fusiformis expressed on the surface of the fd bacteriophage. By utilizing the biomineralizing peptide component displayed on the bacteriophage surface, we found that low concentrations (0.09 mg/mL of the R5 bacteriophage, below the concentration range used in other studies) could be used to create silica nanofibers. An additional benefit of this approach is the ability of our R5-displaying phage to form silica materials without the need for supplementary components, such as aminopropyl triethoxysilane, that are typically used in such processes. Because this method for silica formation can occur under mild conditions when implementing our R5 displaying phage system, we may provide a relatively simple, economical, and environmentally friendly process for creating silica nanomaterials.

Perspectives for biocatalytic lignin utilization: cleaving 4-O-5 and Cα-Cβ bonds in dimeric lignin model compounds catalyzed by a promiscuous activity of tyrosinase

BACKGROUND

In the biorefinery utilizing lignocellulosic biomasses, lignin decomposition to value-added phenolic derivatives is a key issue, and recently biocatalytic delignification is emerging owing to its superior selectivity, low energy consumption, and unparalleled sustainability. However, besides heme-containing peroxidases and laccases, information about lignolytic biocatalysts is still limited till date.

RESULTS

Herein, we report a promiscuous activity of tyrosinase which is closely associated with delignification requiring high redox potentials (>1.4 V vs. normal hydrogen electrode [NHE]). The promiscuous activity of tyrosinase not only oxidizes veratryl alcohol, a commonly used nonphenolic substrate for assaying ligninolytic activity, to veratraldehyde but also cleaves the 4-O-5 and C_α-C_β bonds in 4-phenoxyphenol and guaiacyl glycerol-β-guaiacyl ether (GGE) that are dimeric lignin model compounds. Cyclic voltammograms additionally verified that the promiscuous activity oxidizes lignin-related high redox potential substrates.

CONCLUSION

These results might be applicable for extending the versatility of tyrosinase toward biocatalytic delignification as well as suggesting a new perspective for sustainable lignin utilization. Furthermore, the results provide insight for exploring the previously unknown promiscuous activities of biocatalysts much more diverse than ever thought before, thereby innovatively expanding the applicable area of biocatalysis.

Megasphaera hexanoica sp. nov., a medium-chain carboxylic acid-producing bacterium isolated from a cow rumen

Strain MHT, a strictly anaerobic, Gram-stain-negative, non-spore-forming, spherical coccus or coccoid-shaped microorganism, was isolated from a cow rumen during a screen for hexanoic acid-producing bacteria. The microorganism grew at 30-40 °C and pH 5.5-7.5 and exhibited production of various short- and medium-chain carboxylic acids (acetic acid, butyric acid, pentanoic acid, isobutyric acid, isovaleric acid, hexanoic acid, heptanoic acid and octanoic acid), as well as H2 and CO2 as biogas. Phylogenetic analysis based on 16S rRNA gene sequencing demonstrated that MHT represents a member of the genus Megasphaera, with the closest relatives being Megapsphaera indica NMBHI-10T (94.1 % 16S rRNA sequence similarity), Megasphaera elsdenii DSM 20460T (93.8 %) and Megasphaera paucivorans DSM 16981T (93.8 %). The major cellular fatty acids produced by MHT included C12 : 0, C16 : 0, C18 : 1cis 9, and C18 : 0, and the DNA G+C content of the MHT genome is 51.8 mol%. Together, the distinctive phenotypic and phylogenetic characteristics of MHT indicate that this microorganism represents a novel species of the genus Megasphaera, for which the name Megasphaera hexanoica sp. nov. is herein proposed. The type strain of this species is MHT (=KCCM 43214T=JCM 31403T).

Simple quantification method for N-nitrosamines in atmospheric particulates based on facile pretreatment and GC-MS/MS

Nine N-nitrosamines (i.e., N-nitrosomethylamine, N-nitrosodiethylamine (NDEA), N-nitrosodimethylamine (NDMA), N-nitrosodi-n-propylamine (NDPA), N-nitrosomorpholine (NMor), N-nitrosopyrrolidine (NPyr), N-nitrosopiperidine (NPip), N-nitorosodi-n-butylamine (NDBA), and N-nitrosodiphenylamine (NDPhA) in atmospheric PM_2.5 collected in the fall season from an roadside site and a residential in Seoul, Korea have been analyzed using a newly developed method consisting of simple direct liquid extraction assisted by ultrasonication and subsequent quantification using a gas chromatography-triple quadrupole mass spectrometry (GC-TQMS). Excellent recovery values (92-100%) and method detection limits for the target compounds atmospheric PM samples could be achieved even without an evaporation step for sample concentration. The concentration of total N-nitrosamines in PM_2.5 was ranged from 0.3 to 9.4 ng m^-3 in this study; NDMA, NDEA, NDBA, NPyr, and NMor in PM_2.5 were found to be the most frequently encountered compounds at the sampling sites. Since no industrial plant is located in Seoul, vehicle exhausts were considered major cause of the formation of nitrosamines in this study. The mechanisms how these compounds are formed and detected in the atmosphere are explained from the viewpoint of secondary organic aerosol. Considering the concentrations of N-nitrosamines and their associated potential health risks, a systematic monitoring of nitrosamines present in both ambient air and PM_2.5 including seasonal and diurnal variations of selected sites (including potential precursor sources) should be carried out in the future. The proposed sample pretreatment method along with the analytical method will definitely help us perform the monitoring study.

Pyrosequencing analysis of microbial communities in hollow fiber-membrane biofilm reactors system for treating high-strength nitrogen wastewater

Wastewaters from swine farms, nitrogen-dealing industries or side-stream processes of a wastewater treatment plant (e.g., anaerobic digesters, sludge thickening processes, etc.) are characterized by low C/N ratios and not easily treatable. In this study, a hollow fiber-membrane biofilm reactors (HF-MBfR) system consisting of an O2-based HF-MBfR and an H2-based HF-MBfR was applied for treating high-strength wastewater. The reactors were continuously operated with low supply of O2 and H2 and without any supply of organic carbon for 250 d. Gradual increase of ammonium and nitrate concentration in the influent showed stable and high nitrogen removal efficiency, and the maximum ammonium and nitrate removal rates were 0.48 kg NH4(+)-N m(-3) d(-1) and 0.55 kg NO3(-)-N m(-3) d(-1), respectively. The analysis of the microbial communities using pyrosequencing analysis indicated that Nitrosospira multiformis, ammonium-oxidizing bacteria, and Nitrobacter winogradskyi and Nitrobacter vulgaris, nitrite-oxidizing bacteria were highly enriched in the O2-based HF-MBfR. In the H2-based HF-MBfR, hydrogenotrophic denitrifying bacteria belonging to the family of Thiobacillus and Comamonadaceae were initially dominant, but were replaced to heterotrophic denitrifiers belonging to Rhodocyclaceae and Rhodobacteraceae utilizing by-products induced from autotrophic denitrifying bacteria. The pyrosequencing analysis of microbial communities indicates that the autotrophic HF-MBfRs system well developed autotrophic nitrifying and denitrifying bacteria within a relatively short period to accomplish almost complete nitrogen removal.

Extracellular electron transfer from cathode to microbes: application for biofuel production

Extracellular electron transfer in microorganisms has been applied for bioelectrochemical synthesis utilizing microbes to catalyze anodic and/or cathodic biochemical reactions. Anodic reactions (electron transfer from microbe to anode) are used for current production and cathodic reactions (electron transfer from cathode to microbe) have recently been applied for current consumption for valuable biochemical production. The extensively studied exoelectrogenic bacteria Shewanella and Geobacter showed that both directions for electron transfer would be possible. It was proposed that gram-positive bacteria, in the absence of cytochrome C, would accept electrons using a cascade of membrane-bound complexes such as membrane-bound Fe-S proteins, oxidoreductase, and periplasmic enzymes. Modification of the cathode with the addition of positive charged species such as chitosan or with an increase of the interfacial area using a porous three-dimensional scaffold electrode led to increased current consumption. The extracellular electron transfer from the cathode to the microbe could catalyze various bioelectrochemical reductions. Electrofermentation used electrons from the cathode as reducing power to produce more reduced compounds such as alcohols than acids, shifting the metabolic pathway. Electrofuel could be generated through artificial photosynthesis using electrical energy instead of solar energy in the process of carbon fixation.

Production of medium-chain carboxylic acids by Megasphaera sp. MH with supplemental electron acceptors

BACKGROUND

C5-C8 medium-chain carboxylic acids are valuable chemicals as the precursors of various chemicals and transport fuels. However, only a few strict anaerobes have been discovered to produce them and their production is limited to low concentrations because of product toxicity. Therefore, a bacterial strain capable of producing high-titer C5-C8 carboxylic acids was strategically isolated and characterized for production of medium chain length carboxylic acids.

RESULTS

Hexanoic acid-producing anaerobes were isolated from the inner surface of a cattle rumen sample. One of the isolates, displaying the highest hexanoic acid production, was identified as Megasphaera sp. MH according to 16S rRNA gene sequence analysis. Megasphaera sp. MH metabolizes fructose and produces various medium-chain carboxylic acids, including hexanoic acid, in low concentrations. The addition of acetate to the fructose medium as an electron acceptor increased hexanoic acid production as well as cell growth. Supplementation of propionate and butyrate into the medium also enhanced the production of C5-C8 medium-chain carboxylic acids. Megasphaera sp. MH produced 5.7 g L(-1) of pentanoic acid (C5), 9.7 g L(-1) of hexanoic acid (C6), 3.2 g L(-1) of heptanoic acid (C7) and 1.2 g L(-1) of octanoic acid (C8) in medium supplemented with C2-C6 carboxylic acids as the electron acceptors. This is the first report on the production of high-titer heptanoic acid and octanoic acid using a pure anaerobic culture.

CONCLUSION

Megasphaera sp. MH metabolized fructose for the production of C2-C8 carbon-chain carboxylic acids using various electron acceptors and achieved a high-titer of 9.7 g L(-1) and fast productivity of 0.41 g L(-1) h(-1) for hexanoic acid. However, further metabolic activities of Megaspahera sp. MH for C5-C8 carboxylic acids production must be deciphered and improved for industrially relevant production levels.

Feasibility of a facile butanol bioproduction using planetary mill pretreatment

A facile butanol bioproduction process was developed using planetary milling, and Pinus rigida wood waste as a model substrate for fermentable sugars. The use of planetary milling as the pretreatment eliminates the need for washing and transfer of the biomass prior to enzymatic hydrolysis. Moreover, using this pretreatment process resulted in the production of only 0.072 ± 0.003 g/L soluble phenolic compounds, a concentration that was not inhibitory towards Clostridium beijerinckii NCIMB 8052. As the milling was performed in a compatible buffer (50mM acetate, pH 4.8), the enzymatic hydrolysis step was initiated by simply adding the cellulase cocktail powder directly to pretreated biomass without washing the biomass or exchanging the buffer, resulting in a glucose yield of 31 g/L (84.02%). Fermentation of the hydrolysate samples by C. beijerinckii NCIMB 8052 gave slightly better butanol yields than cultures grown in a typical lab media (P2), with final concentrations of 6.91 and 6.66 g/L, respectively.

Analysis of the Microbial Community in an Acidic Hollow-Fiber Membrane Biofilm Reactor (Hf-MBfR) Used for the Biological Conversion of Carbon Dioxide to Methane

Hydrogenotrophic methanogens can use gaseous substrates, such as H₂ and CO₂, in CH₄ production. H₂ gas is used to reduce CO₂. We have successfully operated a hollow-fiber membrane biofilm reactor (Hf-MBfR) for stable and continuous CH₄ production from CO₂ and H₂. CO₂ and H₂ were diffused into the culture medium through the membrane without bubble formation in the Hf-MBfR, which was operated at pH 4.5–5.5 over 70 days. Focusing on the presence of hydrogenotrophic methanogens, we analyzed the structure of the microbial community in the reactor. Denaturing gradient gel electrophoresis (DGGE) was conducted with bacterial and archaeal 16S rDNA primers. Real-time qPCR was used to track changes in the community composition of methanogens over the course of operation. Finally, the microbial community and its diversity at the time of maximum CH₄ production were analyzed by pyrosequencing methods. Genus Methanobacterium, related to hydrogenotrophic methanogens, dominated the microbial community, but acetate consumption by bacteria, such as unclassified Clostridium sp., restricted the development of acetoclastic methanogens in the acidic CH₄ production process. The results show that acidic operation of a CH₄ production reactor without any pH adjustment inhibited acetogenic growth and enriched the hydrogenotrophic methanogens, decreasing the growth of acetoclastic methanogens.

Caproiciproducens galactitolivorans gen. nov., sp. nov., a bacterium capable of producing caproic acid from galactitol, isolated from a wastewater treatment plant

A strictly anaerobic, Gram-stain-positive, non-spore-forming, rod-shaped bacterial strain, designated BS-1T, was isolated from an anaerobic digestion reactor during a study of bacteria utilizing galactitol as the carbon source. Its cells were 0.3-0.5 μm × 2-4 μm, and they grew at 35-45 °C and at pH 6.0-8.0. Strain BS-1T produced H2, CO2, ethanol, acetic acid, butyric acid and caproic acid as metabolic end products of anaerobic fermentation. Phylogenetic analysis, based on the 16S rRNA gene sequence, showed that strain BS-1T represented a novel bacterial genus within the family Ruminococcaceae, Clostridium Cluster IV. The type strains that were most closely related to strain BS-1T were Clostridium sporosphaeroides KCTC 5598T (94.5 %), Clostridium leptum KCTC 5155T (94.3 %), Ruminococcus bromii ATCC 27255T (92.1 %) and Ethanoligenens harbinense YUAN-3T (91.9 %). Strain BS-1T had 17.6 % and 20.9 % DNA-DNA relatedness values with C. sporosphaeroides DSM 1294T and C. leptum DSM 753T, respectively. The major components of the cellular fatty acids were C16 : 0 dimethyl aldehyde (DMA) (22.1 %), C16 : 0 aldehyde (14.1 %) and summed feature 11 (iso-C17 : 0 3-OH and/or C18 : 2 DMA; 10.0 %). The genomic DNA G+C content was 50.0 mol%. Phenotypic and phylogenetic characteristics allowed strain BS-1T to be clearly distinguished from other taxa of the genus Clostridium Cluster IV. On the basis of these data, the isolate is considered to represent a novel genus and novel species within Clostridium Cluster IV, for which the name Caproiciproducens galactitolivorans gen. nov., sp. nov. is proposed. The type species is BS-1T ( = JCM 30532T and KCCM 43048T).

Enhanced light scattering and trapping effect of Ag nanowire mesh electrode for high efficient flexible organic solar cell

Ag nanowire (NW) mesh is used as transparent conducting electrode for high efficient flexible organic solar cells (OSCs). The Ag NW mesh electrode facilitates light scattering and trapping, allowing enhancement of light absorption in the active layer. OSCs incorporating Ag NW mesh electrode exhibit maximum power conversion efficiency (PCE) of 4.47%, 25%, higher than that of OSCs with a conventional ITO electrode (3.63%).

Effect of geometric lattice design on optical/electrical properties of transparent silver grid for organic solar cells

Silver (Ag) grid transparent electrode is one of the most promising transparent conducting electrodes (TCEs) to replace conventional indium tin oxide (ITO). We systematically investigate an effect of geometric lattice modifications on optical and electrical properties of Ag grid electrode. The reference Ag grid with 5 μm width and 100 μm pitch (duty of 0.05) prepared by conventional photo-lithography and lift-off processes shows the sheet resistance of 13.27 Ω/sq, transmittance of 81.1%, and resultant figure of merit (FOM) of 129.05. Three different modified Ag grid electrodes with stripe added-mesh (SAM), triangle-added mesh (TAM), and diagonal-added mesh (DAM) are suggested to improve optical and electrical properties. Although all three of SAM, TAM, and DAM Ag grid electrodes exhibit the lower transmittance values of about 72 - 77%, they showed much decreased sheet resistance of 6 - 8 Ω/sq. As a result, all of the lattice-modified Ag grid electrodes display significant improvement of FOM and the highest value of 171.14 is obtained from DAM Ag grid, which is comparable to that of conventional ITO electrode (175.46). Also, the feasibility of DAM Ag gird electrode for use in organic solar cell is confirmed by finite difference time domain (FDTD) simulations. Unlike a conventional ITO electrode, DAM Ag grid electrode can induce light scattering and trapping due to the diffuse transmission that compensates for the loss in optical transparency, resulting in comparable light absorption in the photo active layer of poly(3-hexylthiophene) (P3HT): [6,6]-phenyl-C61-butyric acid methyl ester (PC₆₀BM). P3HT:PC₆₀BM based OSCs with the DAM Ag grid electrode were fabricated, which also showed the potential for ITO-free transparent electrode.

Production of hydrogen and volatile fatty acid by Enterobacter sp. T4384 using organic waste materials

In a study of hydrogen-producing bacteria, strain T4384 was isolated from rice field samples in the Republic of Korea. The isolate was identified as Enterobacter sp. T4384 by phylogenetic analysis of 16S rRNA and rpoB gene sequences. Enterobacter sp. T4384 grew at a temperature range of 10-45 degrees C and at an initial pH range of 4.5-9.5. Strain T4384 produced hydrogen at 0-6% NaCl by using glucose, fructose, and mannose. In serum bottle cultures using a complete medium, Enterobacter sp. T4384 produced 1,098 ml/l H2, 4.0 g/l ethanol, and 1.0 g/l acetic acid. In a pH-regulated jar fermenter culture with the biogas removed, 2,202 ml/l H2, 6.2 g/l ethanol, and 1.0 g/l acetic acid were produced, and the lag-phase time was 4.8 h. Strain T4384 metabolized the hydrolysate of organic waste for the production of hydrogen and volatile fatty acid. The strain T4384 produced 947 ml/l H2, 3.2 g/l ethanol, and 0.2 g/l acetic acid from 6% (w/v) food waste hydrolysate; 738 ml/l H2, 4.2 g/l ethanol, and 0.8 g/l acetic acid from Miscanthus sinensis hydrolysate; and 805 ml/l H2, 5.0 g/l ethanol, and 0.7 g/l acetic acid from Sorghum bicolor hydrolysate.

Conversion of levulinic acid to 2-butanone by acetoacetate decarboxylase from Clostridium acetobutylicum

In this study, a novel system for synthesis of 2-butanone from levulinic acid (γ-keto-acid) via an enzymatic reaction was developed. Acetoacetate decarboxylase (AADC; E.C. 4.1.1.4) from Clostridium acetobutylicum was selected as a biocatalyst for decarboxylation of levulinic acid. The purified recombinant AADC from Escherichia coli successfully converted levulinic acid to 2-butanone with a conversion yield of 8.4-90.3 % depending on the amount of AADC under optimum conditions (30 °C and pH 5.0) despite that acetoacetate, a β-keto-acid, is a natural substrate of AADC. In order to improve the catalytic efficiency, an AADC-mediator system was tested using methyl viologen, methylene blue, azure B, zinc ion, and 2,2-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) as mediators. Among them, methyl viologen showed the best performance, increasing the conversion yield up to 6.7-fold in comparison to that without methyl viologen. The results in this study are significant in the development of a renewable method for the synthesis of 2-butanone from biomass-derived chemical, levulinic acid, through enzymatic decarboxylation.

Co-culturing a novel Bacillus strain with Clostridium tyrobutyricum ATCC 25755 to produce butyric acid from sucrose

BACKGROUND

Currently, the most promising microorganism used for the bio-production of butyric acid is Clostridium tyrobutyricum ATCC 25755T; however, it is unable to use sucrose as a sole carbon source. Consequently, a newly isolated strain, Bacillus sp. SGP1, that was found to produce a levansucrase enzyme, which hydrolyzes sucrose into fructose and glucose, was used in a co-culture with this strain, permitting C. tyrobutyricum ATCC 25755T to ferment sucrose to butyric acid.

RESULTS

B. sp. SGP1 alone did not show any butyric acid production and the main metabolite produced was lactic acid. This allowed C. tyrobutyricum ATCC 25755T to utilize the monosaccharides resulting from the activity of levansucrase together with the lactic acid produced by B. sp. SGP1 to generate butyric acid, which was the main fermentative product within the co-culture. Furthermore, the final acetic acid concentration in the co-culture was significantly lower when compared with pure C. tyrobutyricum ATCC 25755T cultures grown on glucose. In fed-batch fermentations, the optimum conditions for the production of butyric acid were around pH 5.50 and a temperature of 37°C. Under these conditions, the final butyrate concentration was 34.2±1.8 g/L with yields of 0.35±0.03 g butyrate/g sucrose and maximum productivity of 0.3±0.04 g/L/h.

CONCLUSIONS

Using this co-culture, sucrose can be utilized as a carbon source for butyric acid production at a relatively high yield. In addition, this co-culture offers also the benefit of a greater selectivity, with butyric acid constituting 92.8% of the acids when the fermentation was terminated.

Comparison of the bacterial communities in anaerobic, anoxic, and oxic chambers of a pilot A(2)O process using pyrosequencing analysis

A(2)O process is a sequential wastewater treatment process that uses anaerobic, anoxic, and oxic chambers for nitrogen and phosphorus removal. In this study, the bacterial communities among these chambers were compared, and the diversity of the bacteria involved in nitrogen and phosphorus removal was surveyed. A pilot-scale A(2)O process (50 m(3) day(-1)) was operated for more than 6 months, and bacterial 16S rRNA gene diversity was analyzed using pyrosequencing. A total of 7,447 bacterial sequence reads were obtained from anaerobic (1,546), anoxic (2,158), and oxic (3,743) chambers. Even though there were differences in the atmospheric condition and functionality, no prominent differences could be found in the bacterial community of the three chambers of the pilot A(2)O process. All sequence reads, which were taxonomically analyzed using the Eztaxon-e database, were assigned into 638 approved or tentative genera. Among them, about 72.2 % of the taxa were contained in the phyla Proteobacteria and Bacteroidetes. Phosphate-accumulating bacteria, Candidatus Accumulibacter phosphatis, and two other Accumulibacter were found to constitute 3.1 % of the identified genera. Ammonia-oxidizing bacteria, Nitrosomonas oligotropha, and four other phylotypes in the same family, Nitrosomonadaceae, constituted 0.2 and 0.9 %, respectively. Nitrite-oxidizing bacteria, Nitrospira defluvii, and other three phylotypes in the same family, Nitrospiraceae, constituted 2.5 and 0.1 %, respectively. In addition, Dokdonella and a phylotype of the phylum Chloroflexi, function in nitrogen and/or phosphate removal of which have not been reported in the A(2)O process, constituted the first and third composition among genera at 4.3 and 3.8 %, respectively.

Identification of Escherichia coli biomarkers responsive to various lignin-hydrolysate compounds

Aberrations in the growth and transcriptome of Escherichia coli str. BL21(DE3) were determined when exposed to varying concentrations of ferulic acid (0.25-1 g/L), an aromatic carboxylic acid identified within lignin-cellulose hydrolysate samples. The expression of several individual genes (aaeA, aaeB, inaA and marA) was significantly induced, i.e., more than 4-fold, and thus these genes and the heat shock response gene htpG were selected as biomarkers to monitor E. coli's responses to five additional hydrolysate-related compounds, including vanillic acid, coumaric acid, 4-hydroxybenzoic acid, ferulaldehyde and furfural. While all of the biomarkers showed dose-dependent responses to most of the compounds, expression of aaeA and aaeB showed the greatest induction (5-30-fold) for all compounds tested except furfural. Lastly, the marA, inaA and htpG genes all showed higher expression levels when the culture was exposed to spruce hydrolysate samples, demonstrating the potential use of these genes as biomarkers.

The future of butyric acid in industry

In this paper, the different applications of butyric acid and its current and future production status are highlighted, with a particular emphasis on the biofuels industry. As such, this paper discusses different issues regarding butyric acid fermentations and provides suggestions for future improvements and their approaches.

Optimization of medium compositions favoring butanol and 1,3-propanediol production from glycerol by Clostridium pasteurianum

Medium compositions favoring butanol and 1,3-propanediol (1,3-PDO) production from glycerol by Clostridium pasteurianum DSM525 were investigated using statistical experimental designs. Medium components affecting butanol and 1,3-PDO production were screened using a fractional factorial experimental design. Among the six tested variables (phosphate buffer, MnSO4·H2O, MgSO4·7H2O, FeSO4·7H2O, (NH4)2SO4, and yeast extract), FeSO4·7H2O, (NH4)2SO4, and yeast extract were found to be significant variables for further optimization of medium using a Box-Behnken design. Optimal butanol (0.98 g/L/h) and 1,3-PDO (1.19 g/L/h) productivities were predicted by the corresponding quadratic model for each product and the models were validated experimentally under optimized conditions. The optimal medium composition for butanol production was significantly different from that for 1,3-PDO production (0.06 vs. 0 g/L for FeSO4·7H2O, 7.35 vs. 0 g/L for (NH4)2SO4, and 5.08 vs. 8.0 g/L for yeast extract), suggesting that the product formation from glycerol by C. pasteurianum DSM525 can be controlled by changing medium compositions.

A biosensor based on the self-entrapment of glucose oxidase within biomimetic silica nanoparticles induced by a fusion enzyme

We constructed a fusion protein (GOx-R5) consisting of R5 (a polypeptide component of silaffin) and glucose oxidase (GOx) that was expressed in Pichia pastoris. Silaffin proteins are responsible for the formation of a silica-based cell matrix of diatoms, and synthetic variants of the R5 protein can perform silicification in vitro[1]. GOx secreted by P. pastoris was self-immobilized (biosilicification) in a pH 5 citric buffer using 0.1M tetramethoxysilane as a silica source. This self-entrapment property of GOx-R5 was used to immobilize GOx on a graphite rod electrode. An electric cell designed as a biosensor was prepared to monitor the glucose concentrations. The electric cell consisted of an Ag/AgCl reference electrode, a platinum counter electrode, and a working electrode modified with poly(neutral red) (PNR)/GOx/Nafion. Glucose oxidase was immobilized by fused protein on poly(neutral red) and covered by Nafion to protect diffusion to the solution. The morphology of the resulting composite PNR/GOx/Nafion material was analyzed by scanning electron microscopy (SEM). This amperometric transducer was characterized electrochemically using cyclic voltammetry and amperometry in the presence of glucose. An image produced by scanning electron microscopy supported the formation of a PNR/GOx complex and the current was increased to 1.58 μA cm(-1) by adding 1mM glucose at an applied potential of -0.5 V. The current was detected by way of PNR-reduced hydrogen peroxide, a product of the glucose oxidation by GOx. The detection limit was 0.67mM (S/N=3). The biosensor containing the graphite rod/PNR/GOx/Nafion detected glucose at various concentrations in mixed samples, which contained interfering molecules. In this study, we report the first expression of R5 fused to glucose oxidase in eukaryotic cells and demonstrate an application of self-entrapped GOx to a glucose biosensor.

Butanol production from thin stillage using Clostridium pasteurianum

The production of butanol from thin stillage by Clostridium pasteurianum DSM 525 was evaluated in the paper. At initial pH values ranging from 5.0 to 7.0 C. pasteurianum DSM 525 produced 6.2-7.2 g/L of butanol utilizing glycerol in thin stillage as the main carbon source, with yields of 0.32-0.44 g butanol produced/g glycerol consumed, which are higher than previously reported yields (e.g., 0.14-0.31 g butanol/g glycerol, Biebl, 2001). Lactic acid in the thin stillage acted as a buffering agent, maintaining the pH of the medium within a range of 5.7-6.1. Lactic acid was also utilized along with glycerol, enhancing butanol production (6.5 g/L butanol vs. 8.7 g/L butanol with 0 and 16 g/L lactic acid, respectively). These results demonstrate the feasibility of cost-effective butanol production using thin stillage as a nutrient-containing medium with a pH buffering capacity.

Effect of biodiesel-derived raw glycerol on 1,3-propanediol production by different microorganisms

The microbial production of 1,3-propanediol (1,3-PD) from raw glycerol, a byproduct of biodiesel production, is economically and environmentally advantageous. Although direct use of raw glycerol without any pretreatment is desirable, previous studies have reported that this could cause inhibition of microbial growth. In this study, we investigated the effects of raw glycerol type, different microorganisms, and pretreatment of raw glycerol on the production of 1,3-PD. Raw glycerol from waste vegetable-oil-based biodiesel production generally caused more inhibition of 1,3-PD production and microbial growth compared to raw glycerol from soybean-oil-based biodiesel production. In addition, two raw glycerol types produced from two biodiesel manufacturers using waste vegetable oil exhibited different 1,3-PD production behavior, partially due to different amounts of methanol included in the raw glycerol from the two biodiesel manufacturers. Klebsiella strains were generally resistant to all types of raw glycerol while the growth of Clostridium strains was variably inhibited depending on the type of raw glycerol. The 1,3-PD production of the Clostridium strains using acid-pretreated raw glycerol was significantly enhanced compared to that with raw glycerol, demonstrating the feasibility of using raw glycerol for 1,3-PD production by various microorganisms.