Continuous polyhydroxybutyrate production from biogas in an innovative two-stage bioreactor configuration

Biogas biorefineries have opened up new horizons beyond heat and electricity production in the anaerobic digestion sector. Added-value products such as polyhydroxyalkanoates (PHAs), which are environmentally benign and potential candidates to replace conventional plastics, can be generated from biogas. This work investigated the potential of an innovative two-stage growth-accumulation system for the continuous production of biogas-based polyhydroxybutyrate (PHB) using Methylocystis hirsuta CSC1 as cell factory. The system comprised two turbulent bioreactors in series to enhance methane and oxygen mass transfer: a continuous stirred tank reactor (CSTR) and a bubble column bioreactor (BCB) with internal gas recirculation. The CSTR was devoted to methanotrophic growth under nitrogen balanced growth conditions and the BCB targeted PHB production under nitrogen limiting conditions. Two different operational approaches under different nitrogen loading rates and dilution rates were investigated. A balanced nitrogen loading rate along with a dilution rate (D) of 0.3 day⁻¹ resulted in the most stable operating conditions and a PHB productivity of ~53 g PHB m⁻³ day⁻¹. However, higher PHB productivities (~127 g PHB m⁻³ day⁻¹) were achieved using nitrogen excess at a D = 0.2 day⁻¹. Overall, the high PHB contents (up to 48% w/w) obtained in the CSTR under theoretically nutrient balanced conditions and the poor process stability challenged the hypothetical advantages conferred by multistage vs single-stage process configurations for long-term PHB production.     

Synthesis and evaluation of the antidepressant activity of the enantiomers of bupropion

The synthesis of the enantiomers of bupropion, (rac)-2-tert-butylamino-3′-chloropropiophenone 1 (Wellbutrin®) is described. The enantiomers were compared with the racemate in both the tetrabenazine-induced sedation model and the inhibition of uptake of biogenic amine assay. No significant differences were found in their potencies to reverse tetrabenazine-induced sedation in mice or in their IC₅₀ values as inhibitors of biogenic amine uptake into nerve endings obtained from mouse brain. © 1993 Wiley-Liss, Inc.     

fliY基因失活减弱沙福芽孢杆菌ST7菌株的锰氧化能力

【背景】沙福芽孢杆菌ST7菌株具有较强的锰氧化能力,但其分子机制不清楚。【目的】着重研究鞭毛马达开关蛋白基因(fliY)对沙福芽孢杆菌锰氧化能力的影响。【方法】根据同源重组原理,以沙福芽孢杆菌ST7菌株为起始菌株,构建fliY基因敲除的突变株ΔfliY,测定菌落迁徙、细菌生物膜和锰氧化率等,研究fliY基因突变后菌株的运动能力、生物膜生成和锰氧化能力是否发生变化。【结果】经克隆测序,证实突变株ΔfliY中fliY基因的后半段被卡纳霉素抗性基因取代,fliY基因失活;与野生型菌株ST7相比,突变株ΔfliY在全营养的LB培养基中生长变化不大,但在含锰的PYCM培养基中,突变株的生长速度减慢、菌落较小、生物膜生成量显著下降,运动性和锰氧化能力分别下降65%和20%。【结论】fliY基因不仅影响菌株的生长和运动,而且参与细菌的趋化和锰氧化等生物学过程。     

油藏注入水靶向脱硫潜力的高温脱硫菌群富集驯化

【背景】海上油田见聚后产出水硫化物超标,影响到注聚水的配聚黏度,采用生物脱硫时,由于常规除硫菌难以适应除油后产出液的高温,使得脱硫效果不佳。【目的】分析海上采出液水处理过程的菌群结构,明确生物处理各节点的菌群构成变化;开展耐高温脱硫菌驯化筛选,获得耐高温的高效脱硫菌。【方法】采集来自胜利油田海三站的水样,以16S rRNA基因高通量测序技术分析样本菌群结构,并分别在不同温度(55、60和65℃)下的无机富集培养基中进行多轮转接驯化,结合常压室温等离子体(atmospheric and room temperature plasma, ARTP)诱变技术筛选获得耐高温的脱硫菌群,采用宏基因组测序技术分析富集菌群的组成,并测定其脱硫能力。【结果】处理前的采出液水样含有较多的嗜热菌和硫酸盐还原菌,如Thermodesulfovibrio、Pseudothermotoga、Thermolithobacter、Fervidobacterium、Thermovenabulales和Pseudomonas;以厌氧气浮除油工艺处理的出水中,嗜氢菌属(Hydrogenophilus)成为最主要的优势菌,...     

First chemical synthesis of a scorpion alpha-toxin affecting sodium channels: the Aah I toxin of Androctonus australis hector.

Aah I is a 63-residue alpha-toxin isolated from the venom of the Buthidae scorpion Androctonus australis hector, which is considered to be the most dangerous species. We report here the first chemical synthesis of Aah I by the solid-phase method, using a Fmoc strategy. The synthetic toxin I (sAah I) was renatured in DMSO-Tris buffer, purified and subjected to thorough analysis and comparison with the natural toxin. The sAah I showed physico-chemical (CD spectrum, molecular mass, HPLC elution), biochemical (amino-acid composition, sequence), immunochemical and pharmacological properties similar to those of the natural toxin. The synthetic toxin was recognized by a conformation-dependent monoclonal anti-Aah I antibody, with an IC50 value close to that for the natural toxin. Following intracerebroventricular injection, the synthetic and the natural toxins were similarly lethal to mice. In voltage-clamp experiments, Na(v) 1.2 sodium channel inactivation was inhibited by the application of sAah I or of the natural toxin in a similar way. This work describes a simple protocol for the chemical synthesis of a scorpion alpha-toxin, making it possible to produce structural analogues in time.     

Soybean isoflavonoids and their metabolic products inhibit in vitro lipoprotein oxidation in serum

Isoflavonoids are compounds present in many legumes, but are derived in the human diet mainly from soybeans and various soybean-based food products. The major isoflavonoids occurring in soy are the glycosides of genistein and daidzein. The metabolic products of genistein metabolism in humans have not been clearly shown. The two main products of daidzein metabolism in humans appear to be equol and O-desmethylangolensin. Increasing evidence suggests that oxidative modification to low-density lipoprotein is involved in atherogenesis, and that natural antioxidants that prevent or inhibit oxidative damage to low-density lipoprotein may beneficially influence atherogenesis. In the present experiments, the effects of genistein and daidzein, and the daidzein metabolites equol and O-desmethylangolensin on Cu²⁺-induced oxidation of lipoproteins in serum were examined. Three concentrations of each compound (0.1 μM, 1 μM, 10 μM) were tested for antioxidant activity in six individual serum samples. All compounds tested inhibited lipoprotein oxidation. The minimum concentration for significant inhibition was 1 μM for genistein and daidzein (P < 0.05), and 0.1 μM equol and O-desmethylangolensin (P < 0.05). Equol and O-desmethylangolensin were more potent inhibitors of in vitro lipoprotein oxidation in serum than the two major dietary isoflavonoids. This study has demonstrated that soybean isoflavonoids and metabolic products of daidzein metabolism inhibit lipoprotein oxidation in vitro. Human intervention studies are needed to determine if these compounds can influence oxidation in vivo.     

Methane emission from a wetland rice field as affected by salinity

The impact of salinity on CH₄ emission was studied by adding salt to a Philippine rice paddy, increasing pore water EC to approx. 4 dS.m^-1 Methane emission from the salt-amended plot and adjacent control plots was monitored with a closed chamber technique. The addition of salt to the rice field caused a reduction by 25% in CH₄ emission. Rates of methane emissions from intact soil cores were measured during aerobic and anaerobic incubations. The anaerobic CH₄ fluxes from the salt-amended soil cores were three to four times lower than from cores of the control plot, whereas the aerobic CH₄ fluxes were about equal. Measurements of the potential CH₄ production with depth showed that the CH₄ production in the salt-amended field was strongly reduced compared to the control field. Calculation of the percentage CH₄ oxidized of the anaerobic flux indicated that CH₄ oxidation in the salt-amended plot was even more inhibited than CH₄ production. The net result was about equal aerobic CH₄ fluxes from both salt-amended plots and non-amended plots. The data illustrate the importance of both CH₄ production and CH₄ oxidation when estimating CH₄ emission and show that the ratio between CH₄ production and CH₄ oxidation may depend on environmental conditions. The reduction in CH₄ emission from rice paddies upon amendment with salt low in sulfate is considerably smaller than the reduction in CH₄ emission observed in a similar study where fields were amended with high-sulfate containing salt (gypsum). The results indicate that CH₄ emissions from wetland rice fields on saline, low-sulfate soils are lower than CH₄ emissions from otherwise comparable non-saline rice tields. However, the reduction in CH₄ emission is not proportional to the reduction in CH₄ production     

Kinetic model of disaccharide oxidation by Agrobacterium tumefaciens

Disaccharides were microbaially transformed to their corresponding 3-keto-derivatives by resting cells of Agrobacterium tumefaciens NCPPB 396. The kinetics and yield of this highly specific oxidation depend on several factors. The oxygen concentration especially has a major influence on the production of 3-keto-derivatives and was investigated kinetically with respect to low stationary oxygen concentrations in solution. Experiments showed unconventional results that conflicted with normal Michaelis-Menten kinetics. A kinetic model was developed and the kinetic constants were calculated. The model and experimental data for sucrose, maltose, iso-maltulose (palatinose), and leucrose are in good agreement with each other. Initial reaction rates with different sugars using constant oxygen concentrations resulted in a Michaelis-Mentent type function. The complete kinetics, including the effect of disaccharide and oxygen concentrations, are presented. (c) 1995 John Wiley & Sons, Inc.     

The oxidation of chiral alcohols catalyzed by catalase in organic solvents

The catalytic properties of bovine liver catalase have been investigated in organic solvents. In tetrahydrofuran, dioxane, and acetone (all containing 1% to 3% of water), the enzyme breaks down tert-butyl hydroperoxide several fold faster than in pure water. Furthermore, the rate of catalase-catalyzed production of tert-butanol from tert-butyl hydroperoxide increases more than 400-fold upon transition from aqueous buffer to ethanol as the reaction medium. The mechanistic rationale for this striking effect is that in aqueous buffer the rate-limiting step of the enzymatic process involves the reduction of catalase's compound I by tert-butyl hydroperoxide. In ethanol, and additional step in the reaction scheme becomes available in which ethanol, greatly outcompeting the hydroperoxide, is oxidized by compound I regenerating the free enzyme. In solvents, such as acetonitrile or tetrahydrofuran, which themselves are not oxidizable by compound I, catalase catalyzes the oxidation of numerous primary and secondary alcohols with tert-butyl hydroperoxide to the corresponding aldehydes or ketones. The enzymatic oxidation of some chiral alcohols (2,3-butanediol, citronellol, and menthol) under these conditions occurs enantioselectively. Examination of the enantioselectivity for the oxidation of 2,3-butanediol in a series of organic solvents reveals a considerable solvent dependence. (c) 1995 John Wiley & Sons, Inc.