Batch anaerobic co-digestion of cow manure and waste milk in two-stage process for hydrogen and methane productions

Anaerobic co-digestion of cow manure (CM) and waste milk (WM), produced by sick cows during treatment with antibiotics, was evaluated in two-stage process under thermophilic condition (55 °C) to determine the effect of WM addition on hydrogen (H₂) and methane (CH₄) production potentials, volatile solids (VS) removal, and energy recovery. Six CM to WM VS ratios of 100:0, 90:10, 70:30, 50:50, 30:70, and 10:90 were examined using 1-L batch digesters. The WM VS ratio of 30 % was found to be the minimum limit for significant increases in specific H₂ and CH₄ yields, and VS removal as compared to digestion of manure alone (P < 0.05). The highest specific H₂ and CH₄ yields, VS removal and energy yield were 38.2 mL/g VS, 627.6 mL/g VS, 78.4 % and 25,459.8 kJ/kg VS, respectively, in CM:WM 30:70. Lag phases to H₂ and CH₄ productions were observed in CM–WM mixtures, increased with increasing the amount of WM in the feedstock and were greater than 72 h in CM:WM 50:50 and 30:70. The digestion system failed in CM:WM 10:90. The results suggest that CM:WM 30:70 was optimum, however, due to limited amount of WM usually generated and long lag phase at this ratio which may make the process uneconomical, CM:WM 70:30 is recommended in practice.     

Bioavailability and metabolism of fucoxanthin in rats: structural characterization of metabolites by LC-MS (APCI)

This study reports bioavailability and metabolism of fucoxanthin (FUCO) from brown algae Padina tetrastromatica in rats. Rats were divided into two groups (n = 25/group). Group one was fed basal diet (control) while the group two received retinol deficient diet (RD group) for 8 weeks. After confirmed RD in blood (0.53 μmol/l), rats were further sub-grouped (n = 5/sub group), intubated a dose of FUCO (0.83 μmol) and killed after 0, 2, 4, 6 and 8 h. The plasma levels (area under curve/8 h) of FUCO (fucoxanthinol (FUOH) + amarouciaxanthin (AAx)) was 2.93 (RD group) and 2.74 pmol/dl (control), respectively. No newly formed retinol was detected in RD rats intubated with FUCO. Besides FUOH (m/z 617 (M+H)⁺) and AAx (m/z 617 (M+H^?)⁺), other deacetylated, hydrolyzed and demethylated metabolites of bearing molecular mass at m/z 600.6 (FUOH–H₂O), m/z 597 (AAx–H₂O), m/z 579 (AAx–2H₂O+1), m/z 551 (AAx–2H₂O–2CH₃+2) and m/z 523 (AAx–2H₂O–4CH₃+4) were also detected in plasma and liver by LC-MS (APCI). Although biological functions of FUCO metabolites need thorough investigation, this is the first detailed report on FUCO metabolites in rats.     

Bioconversion of waste office paper to hydrogen using pretreated rumen fluid inoculum

In this study, a microbial consortium from an acid-treated rumen fluid was used to improve the yields of H₂ production from paper residues in batch reactors. The anaerobic batch reactors, which contained paper and cellulose, were operated under three conditions: (1) 0.5 g paper/L, (2) 2 g paper/L, and (3) 4 g paper/L. Cellulase was added to promote the hydrolysis of paper to soluble sugars. The H₂ yields were 5.51, 4.65, and 3.96 mmol H₂/g COD, respectively, with substrate degradation ranging from 56 to 65.4 %. Butyric acid was the primary soluble metabolite in the three reactors, but pronounced solventogenesis was detected in the reactors incubated with increased paper concentrations (2.0 and 4.0 g/L). A substantial prevalence of Clostridium acetobutylicum (99 % similarity) was observed in the acid-treated rumen fluid, which has been recognized as an efficient H₂-producing strain in addition to ethanol and n-butanol which were also detected in the reactors.     

Dark-Fermentative Biological Hydrogen Production from Mixed Biowastes Using Defined Mixed Cultures

Biological hydrogen (H₂) production from the biowastes is widely recognized as a suitable alternative approach to utilize low cost feed instead of costly individual sugars. In the present investigation, pure and mixed biowastes were fermented by defined sets of mixed cultures for hydrolysis and H₂ production. Under batch conditions, up to 65, 67 and 70 L H₂/kg total solids (2%, TS) were evolved from apple pomace (AP), onion peels (OP) and potato peels (PP) using a combination of hydrolytic mixed culture (MHC5) and mixed microbial cultures (MMC4 or MMC6), respectively. Among the different combinations of mixed biowastes including AP, OP, PP and pea-shells, the combination of OP and PP exhibited maximum H₂ production of 73 and 84 L/kg TS with MMC4 and MMC6, respectively. This study suggested that H₂ production can be effectively regulated by using defined sets of mixed cultures for hydrolysis and H₂ production from pure and mixed biowastes as feed even under unsterile conditions.     

Methanogen genotypes involved in methane formation during anaerobic decomposition of Microcystis blooms at different temperatures

The main goal of this work was to determine which methanogens were present during the anaerobic degradation of Microcystis biomass in the water columns of freshwater lakes. Simulation experiments were performed in which 30 ml Microcystis slurries were anaerobically incubated in 60 ml airtight bottles at three temperatures (15, 25, and 35 °C) for over 90 days. The production of CH₄ was monitored, and the methanogenic community was analyzed by cloning and sequencing the mcrA genes in samples incubated at the three different temperatures. In total, four clusters were detected at different temperatures by phylogenetic analysis of mcrA genes; these included members of Methanomicrobiales, Methanobacteriaceae, and Methanosarcina. An apparent linkage between temperature and phylogeny of the methanogenic community was observed: Methanomicrobiales and Methanobacteriaceae dominated the incubation system at the lower temperatures of 15 and 25 °C, whereas Methanosarcina prevailed at 35 °C. The dominance of these hydrogenotrophic methanogens suggested that, at least at lower temperatures, H₂ and CO₂ might be the primary substrates for CH₄ production during Microcystis anaerobic decomposition.     

Mechanism for the Coupled Photochemistry of Ammonia and Acetylene: Implications for Giant Planets,Comets and Interstellar Organic Synthesis

Laboratory studies provide a fundamental understanding of photochemical processes in planetary atmospheres. Photochemical reactions taking place on giant planets like Jupiter and possibly comets and the interstellar medium are the subject of this research. Reaction pathways are proposed for the coupled photochemistry of NH₃ (ammonia) and C₂H₂ (acetylene) within the context Jupiter’s atmosphere. We then extend the discussion to the Great Red Spot, Extra-Solar Giant Planets, Comets and Interstellar Organic Synthesis. Reaction rates in the form of quantum yields were measured for the decomposition of reactants and the formation of products and stable intermediates: HCN (hydrogen cyanide), CH₃CN (acetonitrile), CH₃CH = N-N = CHCH₃ (acetaldazine), CH₃CH = N-NH₂ (acetaldehyde hydrazone), C₂H₅NH₂ (ethylamine), CH₃NH₂ (methylamine) and C₂H₄ (ethene) in the photolysis of NH₃/C₂H₂ mixtures. Some of these compounds, formed in our investigation of pathways for HCN synthesis, were not encountered previously in observational, theoretical or laboratory photochemical studies. The quantum yields obtained allowed for the formulation of a reaction mechanism that attempts to explain the observed results under varying experimental conditions. In general, the results of this work are consistent with the initial observations of Ferris and Ishikawa (1988). However, their proposed reaction pathway which centers on the photolysis of CH₃CH = N-N = CHCH₃ does not explain all of the results obtained in this study. The formation of CH₃CH = N-N = CHCH₃ by a radical combination reaction of CH₃CH = N? was shown in this work to be inconsistent with other experiments where the CH₃CH = N? radical is thought to form but where no CH₃CH = N-N = CHCH₃ was detected. The importance of the role of H atom abstraction reactions was demonstrated and an alternative pathway for CH₃CH = N-N = CHCH₃ formation involving nucleophilic reaction between N₂H₄ and CH₃CH = NH is advanced.     

Management of soybean oil refinery wastes through recycling them for producing biosurfactant using Pseudomonas aeruginosa MR01

Biosurfactant production through a fermentation process involving the biodegradation of soybean oil refining wastes was studied. Pseudomonas aeruginosa MR01 was able to produce extracellular biosurfactant when it was cultured in three soybean oil refinement wastes; acid oil, deodorizer distillate and soapstock, at different carbon to nitrogen ratios. Subsequent fermentation kinetics in the three types of waste culture were also investigated and compared with kinetic behavior in soybean oil medium. Biodegradation of wastes, biosurfactant production, biomass growth, nitrate consumption and the number of colony forming units were detected in four proposed media, at specified time intervals. Unexpectedly, wastes could stimulate the biodegradation activity of MR01 bacterial cells and thus biosurfactant synthesis beyond that of the refined soybean oil. This is evident from higher yields of biodegradation and production, as revealed in the waste cultures (Y_{deg|(Soybean oil)} = 53.9 % < Y_deg|(wastes) and Y_P/S|(wastes) > Y_{P/S|(Soybean oil)} = 0.31 g g^?1, respectively). Although production yields were approximately the same in the three waste cultures (Y_P/S|(wastes) ? 0.5 g g^?1), microbial activity resulted in higher yields of biodegradation (96.5 ± 1.13 %), maximum specific growth rate (μ _max  = 0.26 ± 0.02 h^?1), and biosurfactant purity (89.6 %) with a productivity of 14.55 ± 1.10 g l^?1, during the bioconversion of soapstock into biosurfactant. Consequently, applying soybean oil soapstock as a substrate for the production of biosurfactant with commercial value has the potential to provide a combination of economical production with environmental protection through the biosynthesis of an environmentally friendly (green) compound and reduction of waste load entering the environment. Moreover, this work inferred spectrophotometry as an easy method to detect rhamnolipids in the biosurfactant products.     

Methane oxidation and methane driven redox process during sequential reduction of a flooded soil ecosystem

A laboratory incubation study conducted to assess the temporal variation of CH₄ oxidation during soil reduction processes in a flooded soil ecosystem. A classical sequence of microbial terminal electron accepting process observed following NO₃ ^? reduction, Fe³⁺ reduction, SO₄ ^2? reduction and CH₄ production in flooded soil incubated under initial aerobic and helium-flushed anaerobic conditions. CH₄ oxidation in the slurries was influenced by microbial redox process during slurry reduction. Under aerobic headspace condition, CH₄ oxidation rate (k) was stimulated by 29 % during 5 days (NO₃ ^? reduction) and 32 % during both 10 days (Fe³⁺) and 20 days (early SO₄ ^2? reduction) over unreduced slurry. CH₄ oxidation was inhibited at the later methanogenic period. Contrastingly, CH₄ oxidation activity in anaerobic incubated slurries was characterized with prolonged lag phase and lower CH₄ oxidation. Higher CH₄ oxidation rate in aerobically incubated flooded soil was related to high abundance of methanotrophs (r?=?0.994, p?<?0.01) and ammonium oxidizers population (r?=?0.184, p?<?0.05). Effect of electron donors NH₄ ⁺, Fe^2+, S^2? on CH₄ oxidation assayed to define the interaction between reduced inorganic species and methane oxidation. The electron donors stimulated CH₄ oxidation as well as increased the abundance of methanotrophic microbial population except S^2? which inhibited the methanotrophic activity by affecting methane oxidizing bacterial population. Our result confirmed the complex interaction between methane-oxidizing microbial groups and redox species during sequential reduction processes of a flooded soil ecosystem.     

Comparison of microbial communities during the anaerobic digestion of <Emphasis Type="Italic">Gracilaria</Emphasis> under mesophilic and thermophilic conditions

Mesophilic and thermophilic anaerobic digesters (MD and TD, respectively) utilizing Gracilaria and marine sediment as the substrate and inoculum, respectively, were compared by analyzing their performances and microbial community changes. During three successive transfers, the average cumulative methane yields in the MD and TD were 222.6 ± 17.3 mL CH₄/g volatile solids (VS) and 246.1 ± 11 mL CH₄/g VS, respectively. The higher hydrolysis rate and acidogenesis in the TD resulted in a several fold greater accumulation of volatile fatty acids (acetate, propionate, and butyrate) followed by a larger pH drop with a prolonged recovery than in the MD. However, the operational stability between both digesters remained comparable. Pyrosequencing analyses revealed that the MD had more complex microbial diversity indices and microbial community changes than the TD. Interestingly, Methanomassiliicoccales, the seventh methanogen order was the predominant archaeal order in the MD along with bacterial orders of Clostridiales, Bacteriodales, and Synergistales. Meanwhile, Coprothermobacter and Methanobacteriales dominated the bacterial and archaeal community in the TD, respectively. Although the methane yield is comparable, both MD and TD show a different profile of pH, VFA and the microbial communities.     

Contribution of Hydrogenase 2 to Stationary Phase H2 Production by Escherichia coli During Fermentation of Glycerol

Escherichia coli has four hydrogenases (Hyd), three genes of which are encoded by the hya, hyb, and hyc operons. The proton-reducing and hydrogen-oxidizing activities of Hyd-2 (hyb) were analyzed in whole cells grown to stationary phase and cell extracts, respectively, during glycerol fermentation using novel double mutants. H₂ production rate at pH 7.5 was decreased by ~3.5- and ~7-fold in hya and hyc (HDK 103) or hyb and hyc (HDK 203) operon double mutants, respectively, compared with the wild type. At pH 6.5, H₂ production decreased by ~2- and ~5-fold in HDK103 and HDK203, respectively, compared with the wild type. At pH 5.5, H₂ production was reduced by ~4.5-fold in the mutants compared with the wild type. The total hydrogen-oxidizing activity was shown to depend on the pH of the growth medium in agreement with previous findings and was significantly reduced in the HDK103 or HDK203 mutants. At pH 7.5, Hyd-2 activity was 0.26 U (mg protein)^?1 and Hyd-1 activity was 0.1 U (mg protein)^?1. As the pH of the growth medium decreased to 6.5, Hyd-2 activity was 0.16 U (mg protein)^?1, and Hyd-1 was absent. Surprisingly, at pH 5.5, there was an increase in Hyd-2 activity (0.33 U mg protein)^?1 but not in that of Hyd-1. These findings show a major contribution of Hyd-2 to H₂ production during glycerol fermentation that resulted from altered metabolism which surprisingly influenced proton reduction.     

Over-expression of l-galactono-γ-lactone dehydrogenase increases vitamin C, total phenolics and antioxidant activity in lettuce through bio-fortification

Epidemiological studies have shown that regular consumption of fruits and vegetables is associated with reduced risk of chronic diseases. Vegetables can provide vitamins, phenolics, flavonoids, minerals and dietary fibers for optimal health benefits. However, some nutrients contained in many fruits and vegetables cannot meet of the complete nutrition need in the human body. Biotechnology has the potential to improve the nutritional value of crops. Considering the high consumption of romaine lettuce in human diet worldwide, the objective of study is to enhance the contents of vitamin C, phenolics and antioxidant activity in lettuce leaves by genetic engineering techniques. The gene expression level, vitamin C content, total phenolics, as well as total and cellular antioxidant activities were analyzed by real-time PCR, HPLC, Folin–Ciocalteu, Hydro-PSC and CAA methods, respectively. The bio-fortification of genetically engineered lettuce increased vitamin C up to 48.94 ± 1.34 mg/100 g FW following the increased over-expression of _At GLDH. This is almost a 3.2-fold increase as the content when compared with wild type lettuce (p < 0.05). In addition, phenolic compounds in transgenic lettuce contained 120.4 ± 1.62 mg GA equiv./100 g FW, almost double the phenolic content of the wild type. Total antioxidant activities were 735.4 ± 47.7 μmol vitamin C equiv./100 g FW, cellular antioxidant activities were 7.33 ± 0.86 μmol quercetin equiv./100 g FW (PBS wash) and 18.14 ± 0.68 μmol quercetin equiv./100 g FW (No PBS wash) in transgenic lettuce, respectively, 1.5, 4 and twofold increases when compared with the wild type. This study suggests that bio-fortification by genetic engineering has great potential to improve vitamin C, phenolic contents and antioxidant activity in lettuce.     

Contribution of winter cover crop amendments on global warming potential in rice paddy soil during cultivation

Background and aims

Winter cover crop cultivation during the fallow season has been strongly recommended in mono-rice paddy soil to improve soil quality, but its impact in increasing the greenhouse gases (GHGs) emissions during rice cultivation when applied as green manure has not been extensively studied. In order to recommend a preferable cover crop which can increase soil productivity and suppress GHG emission impact in paddy soil, the effect of winter cover crop addition on rice yield and total global warming potential (GWP) was studied during rice cultivation.

Methods

Two cover crops (Chinese milk vetch, Astragalus sinicus L., hereafter vetch, and rye, Secale cerealis) having different carbon/nitrogen (C/N) ratios were cultivated during the rice fallow season. The fresh above-ground biomasses of vetch [25 Mg fresh weight (FW) ha^?1, moisture content (MC) 86.9 %, C/N ratio 14.8] and rye (29 Mg rye FW ha^?1, MC 78.0 %, C/N ratio 64.3) were incorporated as green manure 1 week before rice transplanting (NPK + vetch, and NPK + rye). The NPK treatment was installed for comparison as the control. During the rice cultivation, methane (CH₄) and nitrous oxide (N₂O) gases were collected simultaneously once a week using the closed-chamber method, and carbon dioxide (CO₂) flux was estimated using the soil C balance analysis. Total GWP impact was calculated as CO₂ equivalents by multiplying the seasonal CH₄, CO₂, and N₂O fluxes by 25, 1, and 298, respectively.

Results

Methane mainly covered 79–81 % of the total GWP, followed by CO₂ (14–17 %), but the N₂O contribution was very small (2–5 %) regardless of the treatment. Seasonal CH₄ fluxes significantly increased to 61 and 122 % by vetch and rye additions, respectively, compared to that of the NPK treatment. Similarly, the estimated seasonal CO₂ fluxes increased at about 197 and 266 % in the vetch and rye treatments, respectively, compared with the NPK control plots. Based on these results, the total GWP increased to 163 and 221 % with vetch and rye applications, respectively, over the control treatment. Rice productivity was significantly increased with the application of green manure due to nutrient supply; however, vetch was more effective. Total GWP per grain yield was similar with the vetch (low C/N ratio) and NPK treatments, but significantly increased with the rye (high C/N ratio) application, mainly due to its higher CH₄ emission characteristic and lower rice productivity increase.

Conclusions

A low C/N ratio cover crop, such as vetch, may be a more desirable green manure to reduce total GWP per grain yield and to improve rice productivity.     

Strobilanthes crispus attenuates renal carcinogen, iron nitrilotriacetate (Fe-NTA)-mediated oxidative damage of lipids and DNA

This study was aimed to evaluate the effect of Strobilanthes crispus extract for possible protection against lipid peroxidation and DNA damage induced by iron nitrilotriacetate (Fe-NTA) and hydrogen peroxide (H₂O₂). Fe-NTA is a potent nephrotoxic agent and induces acute and subacute renal proximal tubular necrosis by catalyzing the decomposition of H₂O₂-derived production of hydroxyl radicals, which are known to cause lipid peroxidation and DNA damage. Incubation of postmitochondrial supernatant and/or calf thymus DNA with H₂O₂ (40 mM) in the presence of Fe-NTA (0.1 mM) induces lipid peroxidation and DNA damage to about 2.3-fold and 2.9-fold, respectively, as compared to control (P < 0.05). In lipid peroxidation protection studies, S. crispus treatment showed a dose-dependent inhibition (45–53% inhibition, P < 0.05) of Fe-NTA and H₂O₂ induced lipid peroxidation. Similarly, in DNA damage protection studies, S. crispus treatment also showed a dose-dependent inhibition (18–30% inhibition, P < 0.05) of DNA damage. In addition, the protection was closely related to the content of phenolic compounds as evident by S. crispus extract showing the value of 124.48 mg/g total phenolics expressed as gallic acid equivalent (GAE, mg/g of extract). From these studies, it is concluded that S. crispus inhibits peroxidation of membrane lipids and DNA damage induced by Fe-NTA and H₂O₂ and possesses the potential to be used to treat or prevent degenerative diseases where oxidative stress is implicated.     

Production of H2 from cellulose by rumen microorganisms: effects of inocula pre-treatment and enzymatic hydrolysis

H₂ production from cellulose, using rumen fluid as the inoculum, has been investigated in batch experiments. Methanogenic archaea were inhibited by acid pre-treatment, which also inhibited cellulolytic microorganisms, and in consequence, the conversion of cellulose to H₂. Positive results were observed only with the addition of cellulase. H₂ yields were 18.5 and 9.6 mmol H₂ g cellulose^?1 for reactors with 2 and 4 g cellulose l^?1 and cellulase, respectively. H₂ was primarily generated by the butyric acid pathway and this was followed by formation of acetic acid, ethanol and n-butanol. In reactors using 4 g cellulose l^?1 and cellulase, the accumulation of alcohols negatively affected the H₂ yield, which changed the fermentation pathways to solventogenesis. PCR–DGGE analysis showed changes in the microbial communities. The phylogenetic affiliations of the bands of DGGE were 99 % similar to Clostridium sp.     

Kinetics of CH4 production from H2 and CO2 in a hollow fiber reactor by plug flow reaction model

For microbial production of CH₄ from H₂ and CO₂, a hollow fiber reactor had been developed to increase an interfacial area between liquid and gas phases. The CH₄ production with the hollow fiber reactor was analyzed by applying a plug flow reaction model of a tubular reactor. It was possible to apply the model to the reaction of CH₄ production. The relationships between influent gas velocity, length of reactor and reaction yield were simulated by the reaction model. The plug flow reaction model was useful to design a hollow fiber bioreactor for the biomethanation of H₂ and CO₂.     

Microbial Ecophysiology of Whey Biomethanation: Intermediary Metabolism of Lactose Degradation in Continuous Culture

The intermediary carbon and electron flow routes for lactose degradation during whey biomethanation were studied in continuous culture. The chemostat was operated under lactose-limited conditions with a 100-h retention time. The carbon balance observed for lactose degradation was 4.65 mmol of CH₄, 4.36 mmol of CO₂ and 1.15 mmol of cellular carbon per mmol of lactose consumed, with other intermediary metabolites (i.e., acetate, lactate, etc.) accounting for less than 2% of the lactose consumed. The carbon and electron recoveries for this biomethanation were 87 and 90%, respectively. ¹⁴C tracer studies demonstrated that lactose biomethanation occurred in three distinct but simultaneous phases. Lactose was metabolized primarily into lactate, ethanol, acetate, formate, and carbon dioxide. During this hydrolytic phase, 82% of the lactose was transformed into lactate. These metabolites were transformed into acetate and H₂-CO₂ in a second, acetogenic, phase. Finally, the direct methane precursors were transformed during the methanogenic phase, with acetate accounting for 81% of the methane formed. A general scheme is proposed for the exact carbon and electron flow route during lactose biomethanation, which predicts the prevalent microbial populations in this ecosystem.     

Sufficient intake of high amylose cornstarch maintains high colonic hydrogen production for 24 h in rats

Colonic hydrogen (H₂) can suppress oxidative stress and damage in the body. We examined the minimum requirement of high amylose cornstarch (HAS) to maintain high colonic H₂ production for 24 h. Ileorectostomized and sham-operated rats were fed a control diet supplemented with or without 20% HAS for 7 days. Colonic starch utilization was determined. Next, rats were fed the control diet with or without 10% or 20% HAS for 14 or 28 days, respectively. Breath and flatus H₂ excretion for 24 h was measured. 1.04 g of resistant fraction in HAS was utilized for 24 h by colonic bacteria. High H₂ excretion was not maintained for 24 h in rats fed the 10% HAS diet, from which only 0.89 g of resistant starch was estimated to be delivered. High colonic H₂ production for 24 h would be maintained by delivering more HAS to the large intestine than is utilized.     

Polymers of intrinsic microporosity for gas permeation: a molecular simulation study

We report a molecular simulation study for gas permeation in two membranes constructed from polymers of intrinsic microporosity (PIM-1 and PIM-7). With rigid ladder polymer chains, the membranes posses approximately 47.7 and 46.6% fractional free volumes (FFVs) in PIM-1 and PIM-7, respectively. The voids in the membranes have a diameter up to 9 Å and are largely interconnected. The sorption and diffusion of four gases (H₂, O₂, CH₄ and CO₂) were calculated by Monte Carlo and molecular dynamics simulations. The solubility coefficients increase in the order of H₂ < O₂ < CH₄ < CO₂, while the diffusion coefficients increase in the following order: CH₄ < CO₂ < O₂ < H₂. The simulation results agree well with experimental data, particularly for the solubility coefficients. The solubility and diffusion coefficients correlate well separately with the critical temperatures and effective diameters of gases. These molecular-based correlations can be used in the prediction for other gases. As attributed to the microporous structure, PIM-1 and PIM-7 outperform most glassy polymeric membranes in sorption and diffusion. PIM-1 has larger solubility and diffusion coefficients than PIM-7 because the cyano groups in PIM-1 lead to a stronger affinity and a larger FFV. The simulated solubility, diffusivity and permeation selectivities of CO₂/H₂, CO₂/O₂ and CO₂/CH₄ are consistent with experimental data. The quantitative microscopic understanding of gas permeation in the PIM membranes is useful for the new development of high-performance membranes.     

Mevalonate production by engineered acetogen biocatalyst during continuous fermentation of syngas or CO2/H2 blend

Naturally mevalonate-resistant acetogen Clostridium sp. MT1243 produced only 425 mM acetate during syngas fermentation. Using Clostridium sp. MT1243 we engineered biocatalyst selectively producing mevalonate from synthesis gas or CO₂/H₂ blend. Acetate production and spore formation were eliminated from Clostridium sp. MT1243 using Cre-lox66/lox71-system. Cell energy released via elimination of phosphotransacetylase, acetate kinase and early stage sporulation genes powered mevalonate accumulation in fermentation broth due to expression of synthetic thiolase, HMG-synthase, and HMG-reductase, three copies of each, integrated using Tn7-approach. Recombinants produced 145 mM mevalonate in five independent single-step fermentation runs 25 days each in five repeats using syngas blend 60 % CO and 40 % H₂ (v/v) (p < 0.005). Mevalonate production was 97 mM if only CO₂/H₂ blend was fed instead of syngas (p < 0.005). Mevalonate from CO₂/H₂ blend might serve as a commercial route to mitigate global warming in proportion to CO₂ fermentation scale worldwide.