Alkaline Soil Extraction and Subsequent Mineralization of 2,6-Dichlorophenol in a Fixed-Bed Bioreactor

Soil contaminated with moderate concentrations (0.1 g to a few grams) of several chlorophenol (CP) congeners can be remediated by a combination of alkaline extraction and mineralization of the extracted CP in a bioreactor. This method could substitute energy-demanding thermal treatment or space-requiring composting of moderately CP-contaminated soils. 2,6-dichlorophenol (2,6-DCP) served as a model compound to study the alkaline extraction of a loamy sand soil, followed by a biological treatment of the extract. Alkaline extraction is shown to be applicable to different types of soil and a wide range of chlorophenol concentrations. Soil washing was optimal with 10 mM NaOH (pH 12). The procedure yielded 2,6-DCP comparable to amounts obtained by Soxhlet- or ethanol-extraction. With the model soil used in this study, three subsequent extraction steps led to 97% removal of the initially spiked 6.17 mmol 2,6-DCP × kg^-1 soil (=1 g/kg), thus reaching the remediation goal of ≤ 0.2 mmol/kg remaining contaminant concentration. The resulting aqueous extract contained up to 6.8 mM 2,6-DCP and was treated in an aerobic fixed-bed bioreactor. The extraction medium was fed into a recirculation loop in order to dilute the pollutant to concentrations tolerated by the mixed bacterial culture in the reactor. 2,6-DCP was degraded to below the quantification limit (1.8 μiM), and significant detoxification was reached at volumetric loading rates up to 2.1 g/L-d.     

Aerobic Mineralization of 2,6-Dichlorophenol by Ralstonia sp. Strain RK1

A new aerobic bacterium was isolated from the sediment of a freshwater pond close to a contaminated site at Amponville (France). It was enriched in a fixed-bed reactor fed with 2,6-dichlorophenol (2,6-DCP) as the sole carbon and energy source at pH 7.5 and room temperature. The degradation of 2,6-DCP followed Monod kinetics at low initial concentrations. At concentrations above 300 μM (50 mg · liter⁻¹), 2,6-DCP increasingly inhibited its own degradation. The base sequence of the 16S ribosomal DNA allowed us to assign the bacterium to the genus Ralstonia (formerly Alcaligenes). The substrate spectrum of the bacterium includes toluene, benzene, chlorobenzene, phenol, and all four ortho- and para-substituted mono- and dichlorophenol isomers. Substituents other than chlorine prevented degradation. The capacity to degrade 2,6-DCP was examined in two fixed-bed reactors. The microbial population grew on and completely mineralized 2,6-DCP at 2,6-DCP concentrations up to 740 μM in continuous reactor culture supplied with H₂O₂ as an oxygen source. Lack of peroxide completely stopped further degradation of 2,6-DCP. Lowering the acid-neutralizing capacity of the medium to 1/10th the original capacity led to a decrease in the pH of the effluent from 7 to 6 and to a significant reduction in the degradation activity. A second fixed-bed reactor successfully removed low chlorophenol concentrations (20 to 26 μM) with hydraulic residence times of 8 to 30 min.     

Effects of pH and Oxygen on Photosynthetic Reactions of Intact Chloroplasts

Oxygen inhibition of photosynthesis was studied with intact spinach (Spinacia oleracea L.) chloroplasts which exhibited very high rates of photosynthetic CO₂ reduction and were insensitive to additions of photosynthetic intermediates when CO₂ was available at saturating concentrations. Photosynthetic rates were measured polarographically as O₂ evolution, and the extent of the reduction of substrate was estimated from the amount of O₂ evolved. With CO₂ as substrate, inhibition of photosynthesis by O₂ was dependent on pH. At pH values above 8, rates of O₂ evolution were strongly inhibited by O₂ and only a fraction of the added bicarbonate was reduced before O₂ evolution ceased. The extent of O₂ evolution declined with increasing O₂ concentration and decreasing initial bicarbonate concentration. At pH 7.2, the initial photosynthetic rate was inhibited about 30% at high O₂ levels, but the extent of O₂ evolution was unaffected and most of the added bicarbonate was reduced. Photosynthetic O₂ evolution with 3-phosphoglycerate as substrate was similarly dependent on pH and O₂ concentration. In contrast, there was little effect of O₂ and pH on oxaloacetate-dependent oxygen evolution. Acid-base shift experiments with osmotically shocked chloroplasts showed that ATP formation was not affected by O₂. The results are discussed in terms of a balance between photosynthetic O₂ evolution and O₂ consumption by the ribulose diphosphate oxygenase reaction.     

Reduction of 2,6-dichlorophenol-indophenol (Hill Reaction) by Chloroplasts with Different Chlorophyll a/b Ratios Under monochromatic Light

Chloroplasts with different chlorophyll a/b ratios were isolated from 7 to 8 days old wheat seedlings and the activities of reduction of 2,6-dichlorophenol-indophenol (DPIP) by these chloroplasts as function of the chlorophyll a/b ratios were studied under mono-chromatic light (650 m μ, 670 mμ, 680 mμ, 707 mμ). It was found that the DPIP reducing activities by these chloroplasts varied with their chlorophyll a/b ratios, and these variations are affected by the wavelengths of the illuminating light. Under 650 mμ, at the a/b ratios of 2.2 to 2.82, the activities of DPIP reduction in- creased with the a/b ratios, but decreased when the a/b ratios were higher than 2.82. Under 670 mμ, the DPIP reducing activities also varied with the a/b ratios of isolated chloroplasts. However, the variation was more gradual and steadier. Under 680 mμ, the DPIP reducing activities increased with the a/b ratios over 3.0, but decreased rather suddenly at a/b ratio of 3.30. Essentially the same relation held for 707 mμ, but the Hill reaction activities ceased to decline farther when a/b ratio rose to 3.40 at 707 mμ. When the results were analyzed in terms of the “relative activities” of the chloroplasts of the above mentioned wave lengths, it was found that the values of the "relative activity" (a/a+b) declined steadily from 1.47–1.29 at an a/b ratio range of 2.05–3.40, while the values of the "relative activity" (b/a+b)increased steadily from 3.10--4.40 at the same range of a/b ratios. But it is to be noted that, under 650 mμ, the (a/a+b) was 1.36 at the a/b ratio range of 2.63–2.82. Interesting enough, the DPIP reducing activities were the highest of all with these a/b ratios. Activities of DPIP reduction by isolated chloroplasts kept at 0 ℃, 20 ℃, 30 ℃, and 45 ℃ diminished with time when illuminated at all wavelengths. However, for those kept at 45 ℃ their activities were lost after 20 minutes, except those illuminated with the wave length of 680 mμ which still maintained 30 % of the initial activity. When kept at the above mentioned temperatures, the chlorophyll a/b ratios of all batches of chloroplasts declined steadily with time. The above results are interpreted as being indicative of the possibility that the pigment systems for the partial reaction (Hill reaction) of the over-all photosynthesis process consisted mainly of Chlb650 and Chla670. And the correlation of temperature and abolition of activity reduction of DPIP of chloroplasts varied under monochromatic light of different wave lengths.     

高浓度钾对杜氏盐藻叶绿体超微结构的影响

在观察到高浓度K 对杜氏盐藻 (DunaliellasalinaTeod .)生长有显著抑制现象 ,以及初步证明高浓度钾通过抑制杜氏盐藻的光合作用而抑制其生长的基础上 ,探讨了高浓度K 对杜氏盐藻叶绿体超微结构的可能影响。电镜观察表明 ,培养液中加入 10 0mmol/LKCl使叶绿体膨胀 ,类囊体膨大并解体 ,叶绿体中同时大量形成及积累淀粉粒。高pH对盐藻叶绿体超微结构有类似影响。高钾引起的叶绿体超微结构的改变及叶绿体中淀粉粒的积累可能是高K 抑制盐藻光合作用及生长的原因之一。     

Tris(pentachlorophenyl) gold(III) complexes

By reaction of Tl(C₆Cl₅)₂Cl with Au(C₆Cl₅)(tht) (tht = tetrahydrothiophen) or [N(PPh₃)₂] [Au(C₆- Cl₅)Cl] the gold(III) complexes [Au(C₆Cl₅)₃(tht)] or [N(PPh₃)₂][Au(C₆Cl₅)₃Cl] respectively, can be prepared. They are the first tris(pentachlorophenyl)- gold(III) complexes to be reported. The ready displacement of tht by other neutral or anionic ligands leads to the synthesis of Au(C₆Cl₅)₃(Ph₂PCH₂PPh₂) or Q[Au(C₆Cl₅)₃X] (Q=N(PPh₃)₂, PPh₃Me or PPh₂Me₂; X=C₆F₅, SCN, Br or I).     

pH Dependence and Kinetics of Glycolate Uptake by Intact Pea Chloroplasts

Experiments in which [1-¹⁴C]glycolate uptake is carried out in conjunction with measurements of stromal pH indicate that only glycolic acid and not the glycolate anion is crossing the pea (Pisum sativum var. Progress No. 9, Agway) chloroplast envelope. This mechanism of glycolate transport appears to be too slow to account for observed photorespiratory carbon fluxes in C₃ plants.     

pH Dependence and Cofactor Requirements of Photochemical Reactions in Maize Chloroplasts

The pH dependence of the photoreduction of ferricyanide and the photoreduction of NADP from water and photosystem I activity have been compared in isolated chloroplasts from mesophyll and bundle sheath cells of Zea mays. The maximum activity of photoreduction of ferricyanide occurs at pH 8.5 in isolated mesophyll chloroplasts. The addition of methylamine does not cause a marked shift in the pH maximum, but brief sonication lowers the pH maximum to 7.0. In contrast, isolated bundle sheath chloroplasts have a pH maximum at 7.0 and the shape of the pH versus activity curve is similar to that of sonicated mesophyll chloroplasts. When photoreduction of ferricyanide by the isolated chloroplasts is measured at their pH maxima, the values for bundle sheath chloroplasts are about half those of methylamine-treated mesophyll chloroplasts on a chlorophyll basis.     

The pH Dependence of Violaxanthin Deepoxidation in Isolated Pea Chloroplasts

The absorbance change at 505 nm was used to monitor the kinetics of violaxanthin deepoxidation in isolated pea (Pisum sativum) chloroplasts under dark conditions at various pH values. In long-term measurements (65 min) a fast and a slow exponential component of the 505-nm absorbance change could be resolved. The fast rate constant was up to 10 times higher than the slow rate constant. The asymptote value of the fast kinetic component was twice that of the slow component. The pH dependency of the parameters of the fast kinetic component was analyzed from pH 5.2 to pH 7.0. It was found that the asymptote value dropped slightly with increasing pH. The rate constant was zero at pH values greater than 6.3 and showed maximum values at pH values less than 5.8. Hill plot analysis revealed a strong positive cooperativity for the pH dependency of the fast rate constant (Hill coefficient nH = 5.3). The results are discussed with respect to published activity curves of violaxanthin deepoxidation.     

Inhibition of dextransucrase by Zn2+, Ni2+, Co2+, and Tris(hydroxymethyl)aminomethane (Tris)

Initial rate kinetics of polysaccharide formation indicate that Zn2+, Ni2+, and Co2+ inhibit dextransucrase [sucrose: 1,6-alpha-D-glucan 6-alpha-D-glucosyltransferase, EC 2.4.1.5] by binding to two types of metal ion sites. One type consists of a single site and has a low apparent affinity for Ca2+. At the remaining site(s), Ca2+ has a much higher apparent affinity than Zn2+, Ni2+, or Co2+, and prevents inhibition by these metal ions. These findings are consistent with a two-site model previously proposed from studies with Ca2+ and EDTA. Initial rate kinetics also show that Tris is competitive with sucrose, but that, unlike Zn2+, Tris does not bind with significant affinity to a second site. This argues that there is a site which is both the sucrose binding site and a general cation site.     

叶绿体硫氧还蛋白系统的调节机制

硫氧还蛋白(Trx)属于巯基-二硫键氧化还原酶家族, 通过作用于底物蛋白侧链2个半胱氨酸残基之间的二硫键(还原、异构和转移)来调控胞内蛋白的结构和功能。叶绿体Trx系统包括Trx及Trx类似蛋白、铁氧还蛋白(Fd)依赖的硫氧还蛋白还原酶(FTR)和还原型烟酰腺嘌呤二核苷磷酸(NADPH)依赖的硫氧还蛋白还原酶C (NTRC)。除了基质蛋白酶类活性变化及叶绿体蛋白的转运受Trx系统调控之外, 在叶绿体中还存在1条跨类囊体膜的还原势传递途径, 把基质Trx的还原势经跨膜转运蛋白介导, 最终传递给类囊体腔蛋白。FTR和NTRC共同作用维持叶绿体的氧化还原平衡。该文对叶绿体硫氧还蛋白系统的调节机制进行了综述, 同时讨论了叶绿体硫氧还蛋白系统对维持植物光合效率的重要意义。     

不同电子供体对2,4-二氯酚还原脱氯的影响

以葡萄糖、乙酸钠、Fe0、Fe0 葡萄糖、Fe0 乙酸钠作为电子供体,接种未驯化厌氧混合菌,考察2,4-二氯酚(2,4-DCP)的还原脱氯特性及Fe0作为电子供体的最佳作用条件与持续性特征.结果表明:与葡萄糖的作用相比,Fe0 葡萄糖可有效提高目标物脱氯效果;乙酸钠、Fe0及Fe0 乙酸钠均为有效电子供体,其中Fe0作为电子供体时目标物脱氯效果最佳,最佳作用条件为初始pH8.0,Fe0投加量2.0 g/L,4-CP为其主要脱氯中间产物;Fe0可持续供给2,4-DCP还原脱氯所需电子,而乙酸钠不断消耗后其脱氯效果与Fe0作为电子供体有明显差距.     

2,4-Dichlorophenol (DCP) containing wastewater treatment using a hybrid-loop bioreactor

Synthetic wastewater containing 2,4-dichlorophenol (DCP) was biologically treated using a hybrid-loop bioreactor system consisting of a packed column biofilm reactor (PCBR) and an aerated tank with effluent recycle. Effects of the feed DCP concentration on COD, DCP and toxicity removals were investigated. Biomass concentration in the packed column and in the aeration tank decreased with increasing feed DCP content due to toxic effects of DCP on the microorganisms. Low biomass concentrations at high DCP contents resulted in low COD, DCP and toxicity removals. Therefore, percent DCP, COD and toxicity removals decreased with increasing feed DCP content. Nearly 70% COD removal was achieved with a feed DCP content of 380 mg L(-1). The system should be operated with the feed DCP lower than 100 mg L(-1) in order to obtain DCP, COD and toxicity removals above 90%.     

Photo-induced pH Changes in the Vicinity of Isolated Peperomia metallica Chloroplasts

Photo-induced pH changes of the external medium in a regionimmediately adjacent to the surface of individual isolated Peperomiametallica chloroplasts have been measured using antimony pH-micro-electrodcs.The pH changes induced by continuous illumination were composedof two phases: an initial alkalization (phase I) and a subsequentacidification (phase II) of the medium. Both phases were severelysuppressed by DCMU and protonophorous uncouplers but they showeddifferent sensitivity towards DCCD₁ NH₄CI and some other agents.Phase I was selectively inhibited by DCCD and was partiallyrestored upon addition of ATP to DCCD-poisoned chloroplasts.Phase II was inhibited by 1.0 mol m^–3NH₄CI. It appearsfrom these data that phases I and II of light-induced pH changesare determined by different processes. It is suggested thatthe pH increase (phase I) is due to a photosynthetic CO₂ fixationand the pH decrease (phase II) is caused by a light-dependentextrusion of protons from intact chloroplasts. Key words: Transport of protons, intact chloroplasts, Peperomia metallica