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Violacein, a blue-violet compound with a wide range of beneficial bioactivities, is an attractive product for microbial production. Currently, violacein production has been demonstrated in several sugar heterotrophs through metabolic engineering; however, the cost of production remains an obstacle for business ventures. To address this issue, the development of host strains that can utilize inexpensive alternative substrates to reduce production costs would enable the commercialization of violacein. In this study, we engineered a facultative methylotroph, Methylorubrum extorquens AM1, to develop a methanol-based platform for violacein production. By optimizing expression vectors as well as inducer concentrations, 11.7 mg/L violacein production was first demonstrated using methanol as the sole substrate. Considering that unidentified bottlenecks for violacein biosynthesis in the shikimate pathway of M. extorquens AM1 would be difficult to address using generic metabolic engineering approaches, random mutagenesis and site-directed mutagenesis were implemented, and a 2-fold improvement in violacein production was achieved. Finally, by co-utilization of methanol and acetate, a remarkable enhancement of violacein production to 118 mg/L was achieved. Our results establish a platform strain for violacein production from non-sugar feedstocks, which may contribute to the development of an economically efficient large-scale fermentation system for violacein production.

Sustainable production of chemicals and materials from renewable non-food biomass using biorefineries has become increasingly important in an effort toward the vision of 'net zero carbon' that has recently been pledged by countries around the world. Systems metabolic engineering has allowed the efficient development of microbial strains overproducing an increasing number of chemicals and materials, some of which have been translated to industrial-scale production. Fermentation is one of the key processes determining the overall economics of bioprocesses, but has recently been attracting less research attention. In this Review, we revisit and discuss factors affecting the competitiveness of bacterial fermentation in connection to strain development by systems metabolic engineering. Future perspectives for developing efficient fermentation processes are also discussed.

Biodegradable polyhydroxybutyrate (PHB) can be produced from methane by some type II methanotroph such as the genus Methylocystis. This study presents the comparative genomic analysis of a newly isolated methanotroph, Methylocystis sp. MJC1 as a biodegradable PHB-producing platform strain. Methylocystis sp. MJC1 accumulates up to 44.5% of PHB based on dry cell weight under nitrogen-limiting conditions. To facilitate its development as a PHB-producing platform strain, the complete genome sequence of Methylocystis sp. MJC1 was assembled, functionally annotated, and compared with genomes of other Methylocystis species. Phylogenetic analysis has shown that Methylocystis parvus to be the closest species to Methylocystis sp. MJC1. Genome functional annotation revealed that Methylocystis sp. MJC1 contains all major type II methanotroph biochemical pathways such as the serine cycle, EMC pathway, and Krebs cycle. Interestingly, Methylocystis sp. MJC1 has both particulate and soluble methane monooxygenases, which are not commonly found among Methylocystis species. In addition, this species also possesses most of the RuMP pathway reactions, a characteristic of type I methanotrophs, and all PHB biosynthetic genes. These comparative analysis would open the possibility of future practical applications such as the development of organism-specific genome-scale models and application of metabolic engineering strategies to Methylocystis sp. MJC1.

Two putative methylglyoxal synthases, which catalyze the conversion of dihydroxyacetone phosphate to methylglyoxal, from Oceanithermus profundus DSM 14,977 and Clostridium difficile 630 have been characterized for activity and thermal stability. The enzyme from O. profundus was found to be hyperthermophilic, with the optimum activity at 80 °C and the residual activity up to 59% after incubation of 15 min at 95 °C, whereas the enzyme from C. difficile was mesophilic with the optimum activity at 40 °C and the residual activity less than 50% after the incubation at 55 °C or higher temperatures for 15 min. The structural analysis of the enzymes with molecular dynamics simulation indicated that the hyperthermophilic methylglyoxal synthase has a rigid protein structure with a lower overall root-mean-square-deviation value compared with the mesophilic or thermophilic counterparts. In addition, the simulation results identified distinct regions with high fluctuations throughout those of the mesophilic or thermophilic counterparts via root-mean-square-fluctuation analysis. Specific molecular interactions focusing on the hydrogen bonds and salt bridges in the distinct regions were analyzed in terms of interatomic distances and positions of the individual residues with respect to the secondary structures of the enzyme. Key interactions including specific salt bridges and hydrogen bonds between a rigid beta-sheet core and surrounding alpha helices were found to contribute to the stabilisation of the hyperthermophilic enzyme by reducing the regional fluctuations in the protein structure. The structural information and analysis approach in this study can be further exploited for the engineering and industrial application of the enzyme.

By facilitating electron transfer to the hydroxylase diiron center, MMOR-a reductase-serves as an essential component of the catalytic cycle of soluble methane monooxygenase. Here, the X-ray structure analysis of the FAD-binding domain of MMOR identified crucial residues and its influence on the catalytic cycle.

In this study, we performed a kinetic analysis of CO-dependent H2 production by metabolically engineered Thermococcus onnurineus NA1, MC01 in terms of the cell activity as well as mass transfer rate. We conducted continuous cultures with varying dilution rate, CO flow rate, or agitation speed. Despite oscillations in cell density, the cultures reached steady states at all operating conditions. As the dilution rate increased from 0.1 to 0.3 h−1, specific activity of H2 production (SAHP) and volumetric cell production rate were linearly increased. Also, the SAHP remained almost constant at the fixed dilution rate of 0.3 h−1 even though the CO transfer rate was changed by adjusting the CO flow rate or the agitation speed. This relationship could be expressed as a typical Luedeking-Piret model, implying that high cell density culture with a sufficient growth rate is essential to obtain higher H2 productivity. On the other hand, more elevated CO transfer at the same dilution rate improved H2 production rate (HPR) by the increase of the cell density, not in the rise of SAHP. Through the continuous culture, 108 mmol/g-cell/h and 121 mmol/L/h of SAHP and HPR, respectively, could be achieved at a dilution rate of 0.3 h−1 with CO supply rate of 0.07 vvm and agitation speed of 700 rpm. Considering high H2 production activity and long-term stability of the strain over 1,000 h, MC01 is confirmed to have an outstanding potential for CO-dependent H2 production.

Fueled by the recognition of hydrogen as a promising renewable energy source for the future, there have been many attempts to find greener and more economical ways for its production from various sources. In this study, Methylomonas sp. DH-1, a type I methanotroph, was found to produce hydrogen using methane as a sole carbon source, under micro-aerobic conditions; this is analogous to the partial oxidation of methane in a thermochemical process based on metal catalysts. Flask cultures of Methylomonas sp. DH-1 were used to investigate the effects of different culture conditions on hydrogen production, including oxygen levels, methane/oxygen ratios, and initial cell densities. Methylomonas sp. DH-1 could produce hydrogen at an oxygen level below 4%, regardless of the methane content in the flask, implying that the critical factor for hydrogen production is the oxygen level, rather than the methane/oxygen ratio. Moreover, Methylomonas sp. DH-1 shows reversibility in hydrogen production and uptake, because the strain produces hydrogen under micro-aerobic conditions, uptakes it when the oxygen levels increase, and restores the hydrogen production capability when conditions become microaerobic again. Under initial conditions of 30% methane, 70% air, and an OD600nm of 6, hydrogen production was 26.87 μmol and its yields per methane and dry cell weight were 14.98 mmol-H2/mol-CH4 and 101.53 μmol-H2/g DCW, respectively, after 24 h of cultivation.

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.

By facilitating electron transfer to the hydroxylase diiron center, MMOR-a reductase-serves as an essential component of the catalytic cycle of soluble methane monooxygenase. Here, the X-ray structure analysis of the FAD-binding domain of MMOR identified crucial residues and its influence on the catalytic cycle.

Since the 20th century, plastics that are widely being used in general life and industries are causing enormous plastic waste problems since improperly discarded plastics barely degrade and decompose. Thus, the demand for polyhydroxyalkanoates (PHAs), biodegradable polymers with material properties similar to conventional petroleum-based plastics, has been increased so far. The microbial production of PHAs is an environment-friendly solution for the current plastic crisis, however, the carbon sources for the microbial PHA production is a crucial factor to be considered in terms of carbon-neutrality. One‑carbon (C1) resources, such as methane, carbon monoxide, and carbon dioxide, are greenhouse gases and are abundantly found in nature and industry. C1 resources as the carbon sources for PHA production have a completely closed carbon loop with much advances; i) fast carbon circulation with direct bioconversion process and ii) simple fermentation procedure without sterilization as non-preferable nutrients. This review discusses the biosynthesis of PHAs based on C1 resource utilization by wild-type and metabolically engineered microbial host strains via biorefinery processes.

Background Ectoine (1,3,4,5-tetrahydro-2-methyl-4-pyrimidinecarboxylic acid) is an attractive compatible solute because of its wide industrial applications. Previous studies on the microbial production of ectoine have focused on sugar fermentation. Alternatively, methane can be used as an inexpensive and abundant resource for ectoine production by using the halophilic methanotroph, Methylomicrobium alcaliphilum 20Z. However, there are some limitations, including the low production of ectoine from methane and the limited tools for the genetic manipulation of methanotrophs to facilitate their use as industrial strains. Results We constructed M. alcaliphilum 20ZDP with a high conjugation efficiency and stability of the episomal plasmid by the removal of its native plasmid. To improve the ectoine production in M. alcaliphilum 20Z from methane, the ectD (encoding ectoine hydroxylase) and ectR (transcription repressor of the ectABC-ask operon) were deleted to reduce the formation of by-products (such as hydroxyectoine) and induce ectoine production. When the double mutant was batch cultured with methane, ectoine production was enhanced 1.6-fold compared to that obtained with M. alcaliphilum 20ZDP (45.58 mg/L vs. 27.26 mg/L) without growth inhibition. Notably, a maximum titer of 142.32 mg/L was reached by the use of an optimized medium for ectoine production containing 6% NaCl and 0.05 μM of tungsten without hydroxyectoine production. This result demonstrates the highest ectoine production from methane to date. Conclusions Ectoine production was significantly enhanced by the disruption of the ectD and ectR genes in M. alcaliphilum 20Z under optimized conditions favoring ectoine accumulation. We demonstrated effective genetic engineering in a methanotrophic bacterium, with enhanced production of ectoine from methane as the sole carbon source. This study suggests a potentially transformational path to commercial sugar-based ectoine production. Graphical Abstract

Background Bioethanol is one of the most representative eco-friendly fuels developed to replace the non-renewable fossil fuels and is the most successful commercially available bio-conversion technology till date. With the availability of inexpensive carbon sources, such as cellulosic biomass, bioethanol production has become cheaper and easier to perform, which can facilitate the development of methods for converting ethanol into higher value-added biochemicals. In this study, a bioconversion process using Pseudomonas putida as a biocatalyst was established, wherein ethanol was converted to mevalonate. Since ethanol can be converted directly to acetyl-CoA, bypassing its conversion to pyruvate, there is a possibility that ethanol can be converted to mevalonate without producing pyruvate-derived by-products. Furthermore, P. putida seems to be highly resistant to the toxicity caused by terpenoids, and thus can be useful in conducting terpenoid production research. Results In this study, we first expressed the core genes responsible for mevalonate production (atoB, mvaS, and mvaE) in P. putida and mevalonate production was confirmed. Thereafter, through an improvement in genetic stability and ethanol metabolism manipulation, mevalonate production was enhanced up to 2.39-fold (1.70 g/L vs. 4.07 g/L) from 200 mM ethanol with an enhancement in reproducibility of mevalonate production. Following this, the metabolic characteristics related to ethanol catabolism and mevalonate production were revealed by manipulations to reduce fatty acid biosynthesis and optimize pH by batch fermentation. Finally, we reached a product yield of 0.41 g mevalonate/g ethanol in flask scale culture and 0.32 g mevalonate/g ethanol in batch fermentation. This is the highest experimental yield obtained from using carbon sources other than carbohydrates till date and it is expected that further improvements will be made through the development of fermentation methods. Conclusion Pseudomonas putida was investigated as a biocatalyst that can efficiently convert ethanol to mevalonate, the major precursor for terpenoid production, and this research is expected to open new avenues for the production of terpenoids using microorganisms that have not yet reached the stage of mass production.

Native 3-hydroxybutyrate dehydrogenase from Alcaligenes faecalis can catalyze the reversible reduction of acetoacetate, a four carbon chain oxo acid. This enzyme has been engineered to enable the reduction of levulinic acid, with one carbon longer than acetoacetate. In this study, the native and engineered enzymes were subjected to the catalysis of oxo acids with a carbon chain length of 3 to 8, in order to examine the capability of the enzyme to work on various platform chemicals. The engineered enzyme could reduce the C7 and C8 oxo acids whereas the wild-type had no activity on these substrates. Docking simulation has indicated Tyr155 and Ser142 are key residues for the catalysis. In addition, stable hydrogen bond formation between Gln196 and the substrates affects the turnover rate. Mutation sites in the engineered enzyme were focused on creating larger active site volume for substrates with extended chain lengths. Both qualitative and quantitative structural basis for the enzyme substrate specificity on alpha, beta, gamma and omega hydroxy acids could be elucidated.

We investigated the algorithm analysis of the bubble generation in a microfluidic device to study the effect of the surface tension and the flow rate on the microbubble size. For the analysis of the surface tension, five different solutions were used: 3.5% brine, mineral oil, 1% polyethylene glycol (PEG) 400, 1% tween 80, and 1% triton X-100. The various flow rates were also employed: 5~15 µL/min for the liquid and 100~200 mL/min for the gas phase. The size of the bubble was measured via the algorithm analysis and the bubble defect was also detected by c chart. We observed that the microbubble size was affected by the flow rates of solution and the gas. Hence, we developed an equation to estimate the size through the flow rate ratio between the solution and gas phase, showing that the microbubble size could be controlled by the liquid properties or the flow rates. Therefore, this algorithm-based microfluidic device could be a powerful tool for generating gas micro-bubbles in a controlled manner.

Propane is the main component of liquefied petroleum gas and is derived from crude oil processing. Methanotrophic bacteria can convert various alkanes using methane monooxygenase enzyme to primary alcohols. These are further oxidized to various aldehydes by alcohol dehydrogenases or methanol dehydrogenases. In this study, 2-propanol was produced from propane using the whole cells of Methylosinus trichosporium OB3b, Methylomicrobium alcaliphilum 20Z, and Methylomonas sp. DH-1 as the biocatalysts. The biocatalytic process of converting propane to 2-propanol was optimized by the use of several inhibitors and additives, such as EDTA, sodium phosphate, and sodium formate to prevent oxidation of 2-propanol to acetone and to enhance conversion of propane to propanol. The maximum titer of 2-propanol was 0.424 g/L, 0.311 g/L, and 0.610 g/L for Methylomonas sp. DH-1, M. alcaliphilum 20Z, and M. trichosporium OB3b whole cells, respectively. These results showed that type I and type II methanotrophs could be used as the potent biocatalyst for conversion of propane to propanol.

A solvent-free co-production process for biodiesel and glycerol carbonate (GC) was developed based on enzyme (Novozyme 435). Glycerol obtained from transesterification reactions could be directly converted to GC. The reactions were optimized using the response surface methodology (RSM) separately. The optimal factors, which are enzyme loading, molar ratio of dimethyl carbonate to soybean oil, water content, and reaction temperature, were derived from the response optimizer. The results of optimization for biodiesel and GC production were re-analyzed by overlapping the contour plots of the factors. The following were the optima obtained: enzyme loading of 25 g/L, molar ratio of 15:1, water content of 0.082% (v/v), and reaction temperature of 59.65 °C. When the co-production of biodiesel and GC was conducted using the optima, biodiesel and GC production were achieved with conversions of 97.6% and 95.5%, respectively.

The production of industrial chemicals from renewable biomass resources is a promising solution to overcome the society’s dependence on petroleum and to mitigate the pollution resulting from petroleum processing. Klebsiella pneumoniae is a nutritionally versatile bacterium with numerous native pathways for the production of well-known and industrially important platform chemicals derived from various sugars. Genomic sequence analyses have shown that the K. pneumoniae genome has a high similarity with that of Escherichia coli, the most studied organism, which is used in industrial biotechnology processes for fuel and chemical production. Hence, K. pneumoniae can be considered as a promising platform microorganism that can be metabolically engineered for the high-level production of bio-based chemicals. This review highlights the substrate metabolism and the metabolic engineering strategies developed in K. pneumoniae for the production of bio-based chemicals.

The Two-component Regulatory System (TCS) is the primary mode that bacteria use to continuously sense the environment. A TCS is comprised of a periplasmic sensor Histidine kinase (HK) domain and a cytoplasmic Response regulator (RR) domain. The HK domain phosphorylates the RR domain to activate the effector gene expression. Utilizing a rational approach, the sensor HK was genetically engineered in Escherichia coli to create chimeric HK, by a rewiring or domain swapping strategy. Apart from the wild-type characteristics, chimeric HK imparts novel or the desired characteristics and ability to genetically engineered E. coli for its adaptation and survival. This review focuses on the design, potential applications, and future perspectives of chimeric HKs used as high throughput screening biosensors of various compounds.

Cupriavidus necator, a versatile microorganism found in both soil and water, can have both heterotrophic and lithoautotrophic metabolisms depending on environmental conditions. C. necator has been extensively examined for producing Polyhydroxyalkanoates (PHAs), the promising polyester alternatives to petroleum-based synthetic polymers because it has a superior ability for accumulating a considerable amount of PHAs from renewable resources. The development of metabolically engineered C. necator strains has led to their application for synthesizing biopolymers, biofuels and biochemicals such as ethanol, isobutanol and higher alcohols. Bio-based processes of recombinant C. necator have made much progress in production of these high-value products from biomass wastes, plastic wastes and even waste gases. In this review, we discuss the potential of C. necator as promising platform host strains that provide a great opportunity for developing a waste-based circular bioeconomy.

Auto-generative high pressure digestion (AHPD) and hydrogen-injecting digestion (HID) have been introduced to directly produce high CH4-content biogas from anaerobic digester. However, each approach has its own technical difficulties (pH changes), and practical issues (high cost of H2) to obtain > 90% CH4 containing biogas, particularly, from the high-strength waste like food waste (FW). To overcome this problem, in this study, AHPD and HID were integrated, which can offset each drawback but maximize its benefit. Substrate concentration of FW tested here was 200 g COD/L, the highest ever applied in AHPD and HID studies. At first, the reactor was operated by elevating the autogenerative pressure from 1 to 3, 5, and 7 bar without H2 injection. With the pressure increase, the CH4 content in the biogas gradually increased from 52.4% at 1 bar to 77.4% at 7 bar. However, a drop of CH4 production yield (MPY) was observed at 7 bar, due to the pH drop down to 6.7 by excess CO2 dissolution. At further operation, H2 injection began at 5 bar, with increasing its amount. The injection was effective to increase the CH4 content to 82.8%, 87.2%, and 90.6% at 0.09, 0.13, and 0.18 L H2/g CODFW.fed of H2 injection amount, respectively. At 0.25 L H2/g CODFW.fed, there was a further increase of CH4 content to 92.1%, but the MPY was dropped with pH increase to 8.7 with residual H2 being detected (4% in the biogas). Microbial community analysis showed the increased abundance of piezo-tolerant microbe with pressure increase, and direct interspecies electron transfer contributors after H2 injection. In conclusion, the integration of two approaches enabled to directly produce high calorific biogas (90% > CH4, 180 MJ/m3 biogas) from high-strength FW at the lowest requirement of H2 (0.18 L H2/g CODFW.fed) ever reported.

Microbial biotransformation of CH

Here, we report an analysis method for determining PHA (polyhydroxyalkanoates) contents and their monomer composition in microbial cells based on pyrolysis gas chromatography combined with mass spectrometry (Py-GC/MS). Various kinds of microbial cells accumulating different PHA contents and monomer compositions were prepared through the cultivation of Ralstonia eutropha and recombinant Escherichia coli. Py-GC/MS could analyse these samples in a short time without complicated pretreatment steps. Characteristic peaks such as 2-butenoic acid, 2-pentenoic acid, and hexadecanoic acid regarding PHA compositions and cell components were identified. Considering constituents of cells and ratios of peak areas of dehydrated monomers to hexadecanoic acid, a simple equation for estimation of PHA contents in microbial cells was derived. Also, monomer compositions of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) in R. eutropha could be successfully determined based on peak area of 2-butenoic acid and 2-pentenoic acid of Py-GC/MS, which are the corresponding species of 3-hydroxybutyrate (3HB) and 3-hydroxyvalerate (3HV) in PHBV. Correlation of results between GC-FID and Py-GC/MS could be fitted very well. This method shows similar results for the samples obtained from same experimental conditions, allowing rapid and reliable analysis. Py-GC/MS can be a promising tool to rapidly screen PHA-positive strains based on polymer contents along with monomer compositions.

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.

Immuno-assay is one of diagnostic methods that usually measures biomarkers associated with cancers. However, this method is complex and take a long time to analyze. To overcome these disadvantages, many immuno-sensing chips have been designed and developed. However, these devices still require an external pump or electrical source. In this study, our group fabricated a capillary microfluidic device using glass and adhesive polyethylene terephthalate (PET) film, which were designed by simply patterning and cutting to make the microfluidic capillary channels. Using capillary force alone, glass microfluidic chip can control the speed of fluid-flow and the flow sequence by adjusting the width of the channel and design. In addition, each flow can push out other flow without mixing. The glass-based capillary microfluidic chip (GCMC) can automatically perform immunoassay in regular order without external devices and it provide an electrochemical signal analysis in an average of 2 min. The concentration of the prostate-specific antigen (PSA), a biomarker of prostate cancer, was measured by cyclic voltammetry (CV). In conclusion, GCMC can detect between a range of 100 pg/ml to 1 μg/ml of PSA and provide high selectivity to PSA.

Creating a module that achieves sustainable CO2 capture while being compatible with the existing industry is paramount in overcoming the current CO2-driven environmental issues. This paper presents...

World-wide production of l-lysine has rapidly increased in recent years. In the industrial scale production, it is cost effective to minimize waste as many waste materials are generated during downstream processing. Therefore, the conversion of crude lysine to a more valuable product reduces waste emission. In this study, 1,5-diaminopentane (DAP, trivial name: cadaverine) was produced by l-lysine decarboxylation using Hafnia alvei. The conditions of enzymatic reaction were determined. In particular, the addition of specific detergent (Brij 56) was significantly affected in the bioconversion system. Addition of hydrophobic organic solvent improved the mixing of the reactants. Finally, an industrial crude form of lysine served as a substrate. The DAP conversion by analytical, feed and industrial crude l-lysine was 93.9%, 90.3%, and 63.8%, respectively.

Here, we developed a pressurized bioreactor system that increase carbon monoxide (CO) transfer efficiency in order to enhance the hydrogen productivity in the microbial water gas shift reaction by Thermococcus onnurineus NA1. The effects of CO pressure on the hydrogen production rate, CO consumption rate and the cell growth were investigated using small scale stainless steel bottles at various CO partial pressures. It was found that CO solubility increased by applying pressure can affect hydrogen production positively as long as the increased toxicity of CO is endurable to cells. The hydrogen productivity increased to some extent with CO pressure, but decreased drastically at the pressure higher than 4 bar. On the other hand, the effect of pressure itself on the cell's activity was not as significant as that of CO solubility increase. In the experiments at various system pressures with identical CO partial pressure of 1 bar, more than 80% of the cell activity remains even at total pressure of 10 bar. Also, it was important to determine the appropriate time to increase pressure for preventing excess CO in the reactor. Based on these results, a fermentation strategy for the pressurized system was designed and applied to a 5 L bioreactor with the continuous supply of the gas containing 60% CO. When the pressure was introduced to the bioreactor up to 4 bar at CO limitation condition, the unprecedented high productivity (360 mmol L−1 h−1) could be obtained.

The purpose of this study was to simultaneously produce biodiesel and glycerol carbonate. Glycerol carbonate is a high-value material that could be obtained from glycerol. Response surface methodology was used to perform optimization of simultaneous enzymatic production of biodiesel and glycerol carbonate. Independent factors for optimization of simultaneous enzymatic production included enzyme concentration, a molar ratio of dimethyl carbonate to soybean oil, and reaction temperature. The levels of satisfaction with the production reaction model for biodiesel and glycerol carbonate were high, 0.994 and 1, respectively. The optimum condition for simultaneous production was 116.76 g/L enzyme concentration, 9.27:1 molar ratio, and 52.56 °C reaction temperature. Under the optimum condition, biodiesel 96.3% and glycerol carbonate 99.7% were produced at the same time.

The present study focused on the effect of reducibility of support oxide (CeO2, ZrO2, TiO2, and Al2O3) over the activity of cobalt-based catalysts in high temperature water-gas shift (HT-WGS) reaction. The H2 temperature programmed reduction (TPR) and CO chemisorption characterization results showed that dispersion of cobalt over the support was increased with the increase of the reducibility of the support oxide. The supported catalysts were characterized by X-ray diffraction (XRD) and N2 adsorption–desorption. The results indicated that the Co/CeO2 catalyst possesses the highest surface area and metal dispersion in the series; Co/CeO2 > Co/ZrO2 > Co/Al2O3 > Co/TiO2. The activity results showed that Co/CeO2 was the highly active among the tested catalysts in the temperature range of 350–550 °C. Moreover, the time-on-stream study revealed that the Co/CeO2 catalyst was relatively more stable than cobalt supported on ZrO2 and Al2O3 oxides. The excellent activity and stability of the Co/CeO2 catalyst were attributed to its high metal dispersion, which is found strongly dependent on the reducible nature of the support.

Coal is one of the major sources of energy, fuel, and other related chemicals. The processes to utilize coal for energy, fuel and other chemicals such as coal combustion, liquefaction, carbonization, and gasification pose a great threat to the environment by emitting toxic particles and CO2 to the atmosphere. Thus, biological beneficiation of coal can be a good strategy to utilize coal with environmental sustainability. Here, we report the screening of microorganisms able to degrade or depolymerize coal. These host strains are potential candidates for the development of biological treatment process of coal. A total of 45 microbial strains were isolated from sludge enriched with coal and were identified based on 16S rRNA sequencing. Four strains of three genera, Cupriavidus sp., Pseudomonas sp., and Alcaligenes sp., were further characterized for their abilities to degrade coal. The degree of coal degradation was analyzed by measuring the increase in absorbance at 450 nm by UV spectroscopy. These microorganisms were also able to increase the pH of the culture media as a response to the acidic nature of coal. Laccase-like activity was also found in these strains when tested for RBBR dye degradation. Since biological degradation of coal through the use of microorganisms is a good alternative to chemical combustion of coal, microbial strains isolated in this study can be potential biological catalysts for coal conversion into valuable chemicals.