A kinetic model for surfactant inhibition of pentachlorophenol biodegradation

A kinetic model is used to describe the effect of the nonionic surfactant Tergitol NP-10 (TNP10) on pentachlorophenol (PCP) biodegradation by Sphingomonas chlorophenolica sp. strain RA2. Different initial biomass to initial substrate ratios ranging from 13 to 418 were tested with 23 TNP10 concentrations ranging from 0 to 1500 mg/L. Tests were also conducted at 10 degrees C and 20 degrees C. No PCP biodegradation inhibition was observed at concentrations below the critical micelle concentration (CMC) of 50 mg/L. TNP10 concentrations above 100 to 200 mg/L were increasingly inhibitory to PCP biodegradation rates. This inhibition was best described by the Monod kinetic equation wherein the effect of TNP10 inhibition is reflected in the half-saturation constant (Ks). The value of the Ks increased from between 1.5 and 13.5 mg/L with no surfactant present to 44 to 131 mg/L at 1000 mg/L TNP10. Using a standard competitive inhibition approach, the inhibition constant for TNP10 was approximately 100 mg/L at both 10 degrees C and 20 degrees C.     

Production of galacto-oligosaccharides from lactose by Aspergillus oryzae beta-galactosidase immobilized on cotton cloth.

The production of galacto-oligosaccharides (GOS) from lactose by A. oryzae beta-galactosidase immobilized on cotton cloth was studied. The total amounts and types of GOS produced were mainly affected by the initial lactose concentration in the reaction media. In general, more and larger GOS can be produced with higher initial lactose concentrations. A maximum GOS production of 27% (w/w) of initial lactose was achieved at 50% lactose conversion with 500 g/L of initial lactose concentration. Tri-saccharides were the major types of GOS formed, accounting for more than 70% of the total GOS produced in the reactions. Temperature and pH affected the reaction rate, but did not result in any changes in GOS formation. The presence of galactose and glucose at the concentrations encountered near maximum GOS greatly inhibited the reactions and reduced GOS yield by as much as 15%. The cotton cloth as the support matrix for enzyme immobilization did not affect the GOS formation characteristics of the enzyme, suggesting no diffusion limitation in the enzyme carrier. The thermal stability of the enzyme increased approximately 25-fold upon immobilization on cotton cloth. The half-life for the immobilized enzyme on cotton cloth was more than 1 year at 40 degrees C and 48 days at 50 degrees C. Stable, continuous operation in a plugflow reactor was demonstrated for 2 weeks without any apparent problem. A maximum GOS production of 21 and 26% (w/w) of total sugars was attained with a feed solution containing 200 and 400 g/L of lactose, respectively, at pH 4.5 and 40 degrees C. The corresponding reactor productivities were 80 and 106 g/L/h, respectively, which are at least several-fold higher than those previously reported.     

A continuous thermal lysis procedure for the large-scale preparation of plasmid DNA

There is an increasing interest and need for the development of scaleable process for the preparation of plasmid DNA for vaccines and gene therapy. In this report, we describe a streamline modified process of plasmid extraction based on boiling lysis in order to simplify the operation and process large volumes of Escherichia coli cultures. The bacteria, harvested using a hollow fiber cartridge after fermentation, were treated with lysozyme at 37 degrees C prior to passing through a heat-exchanger coil. Subsequently, the supernatant was separated from lysed bacteria using a 65 microm nylon filter. The employment of a peristaltic pump and two heating coils at constant temperature without the use of centrifugation enabled the process protocol to be constant and controllable. A relatively low lysis temperature of approximately 70-80 degrees C and a buffer modified for the high-density cultures were also optimized for the process. Prior to thermal lysis, a pre-treatment step with the lysozyme for 20 min at 37 degrees C was one of the crucial steps contributing to the high plasmid quantity and quality from batch to batch. After harvesting 17 L of E. coli cultures (OD600 = 50), the plasmid can be extracted within 45 min with this streamline protocol. The plasmid yields are approximately 100mg/L culture, which makes it attractive and promising for the large-scale preparation of plasmid.     

Evidence of UCP1-independent regulation of norepinephrine-induced thermogenesis in brown fat

To study the thermal response of interscapular brown fat (IBF) to norepinephrine (NE), urethan-anesthetized rats (1.2 g/kg ip) maintained at 28-30 degrees C received a constant venous infusion of NE (0-2 x 10(4) pmol/min) over a period of 60 min. IBF temperatures (T(IBF)) were recorded with a small thermistor fixed under the IBF pad. Data were plotted against time and expressed as maximal variation (Deltat degrees C). Saline-injected rats showed a decrease in T(IBF) of approximately 0.6 degrees C. NE infusion increased T(IBF) by a maximum of approximately 3.0 degrees C at a dose of 10(4) pmol x min(-1) x 100 g body wt(-1). Surgically thyroidectomized (Tx) rats kept on 0.05% methimazole showed a flat response to NE. Treatment with thyroxine (T(4), 0.8 microg x 100 g(-1) x day(-1)) for 2-15 days normalized mitochondrial UCP1 (Western blotting) and IBF thermal response to NE, whereas iopanoic acid (5 mg x 100 g body wt(-1) x day(-1)) blocked the effects of T(4). Treatment with 3,5, 3'-triiodothyronine (T(3), 0.6 microg x 100 g body wt(-1) x day(-1)) for up to 15 days did not normalize UCP1 levels. However, these animals showed a normal IBF thermal response to NE. Cold exposure for 5 days or feeding a cafeteria diet for 20 days increased UCP1 levels by approximately 3.5-fold. Nevertheless, the IBF thermal response was only greater than that of controls when maximal doses of NE (2 x 10(4) pmol/min and higher) were used. Conclusions: 1) hypothyroidism is associated with a blunted IBF thermal response to NE; 2) two- to fourfold changes in mitochondrial UCP1 concentration are not necessarily translated into heat production during NE infusion.     

Immobilization of beta-galactosidase on fibrous matrix by polyethyleneimine for production of galacto-oligosaccharides from lactose

The production of galacto-oligosaccharides (GOS) from lactose by Aspergillus oryzae beta-galactosidase immobilized on cotton cloth was studied. A novel method of enzyme immobilization involving PEI-enzyme aggregate formation and growth of aggregates on individual fibrils of cotton cloth leading to multilayer immobilization of the enzyme was developed. A large amount of enzyme was immobilized (250 mg/g support) with about 90-95% efficiency. A maximum GOS production of 25-26% (w/w) was achieved at near 50% lactose conversion from 400 g/L of lactose at pH 4.5 and 40 degrees C. Tri- and tetrasaccharides were the major types of GOS formed, accounting for about 70% and 25% of the total GOS produced in the reactions, respectively. Temperature and pH affected not only the reaction rate but also GOS yield to some extend. A reaction pH of 6.0 increased GOS yield by as much as 10% compared with that of pH 4.5 while decreased the reaction rate of immobilized enzyme. The cotton cloth as the support matrix for enzyme immobilization did not affect the GOS formation characteristics of the enzyme under the same reaction conditions, suggesting diffusion limitation was negligible in the packed bed reactor and the enzyme carrier. Increase in the thermal stability of PEI-immobilized enzyme was also observed. The half-life for the immobilized enzyme on cotton cloth was close to 1 year at 40 degrees C and 21 days at 50 degrees C. Stable, continuous operation in a plug-flow reactor was demonstrated for about 3 days without any apparent problem. A maximum GOS production of 26% (w/w) of total sugars was attained at 50% lactose conversion with a feed containing 400 g/L of lactose at pH 4.5 and 40 degrees C. The corresponding reactor productivity was 6 kg/L/h, which is several-hundred-fold higher than those previously reported.     

Isolation and characterization of IIAChb, a soluble protein of the enzyme II complex required for the transport/phosphorylation of N, N'-diacetylchitobiose in Escherichia coli

N,N'-Diacetylchitobiose is transported/phosphorylated in Escherichia coli by the (GlcNAc)(2)-specific Enzyme II permease of the phosphoenolpyruvate:glycose phosphotransferase system. IIA(Chb), one protein of the Enzyme II complex, was cloned and purified to homogeneity. IIA(Chb) and phospho-IIA(Chb) form stable homodimers (). Phospho-IIA(Chb) behaves as a typical epsilon2-N (i.e. N-3) phospho-His protein. However, the rate constants for hydrolysis of phospho-IIA(Chb) at pH 8.0 unexpectedly increased 7-fold between 25 and 37 degrees C and increased approximately 4-fold with decreasing protein concentration at 37 degrees C (but not 25 degrees C). The data were explained by thermal denaturation studies using CD spectroscopy. IIA(Chb) and phospho-IIA(Chb) exhibit virtually identical spectra at 25 degrees C (approximately 80% alpha-helix), but phospho-IIA(Chb) loses about 30% of its helicity at 37 degrees C, whereas IIA(Chb) shows only a slight change. Furthermore, the T(m) for thermal denaturation of IIA(Chb) was 54 degrees C, only slightly affected by concentration, whereas the T(m) for phospho-IIA(Chb) was much lower, ranging from 40 to 46 degrees C, depending on concentration. In addition, divalent cations (Mg(2+), Cu(2+), and Ni(2+)) have a dramatic and differential effect on the structure, depending on the state of phosphorylation of the protein. Thus, phosphorylation destabilizes IIA(Chb) at 37 degrees C, potentially affecting the monomer/dimer transition, which correlates with its chemical instability at this temperature. The physiological consequences of this phenomenon are briefly considered.     

Acetate Degradation at 70 degrees C in Upflow Anaerobic Sludge Blanket Reactors and Temperature Response of Granules Grown at 70 degrees C

Anaerobic acetate degradation at 70 degrees C and at 55 degrees C (as a reference) was studied by running laboratory upflow anaerobic sludge blanket (UASB) reactors inoculated with mesophilic granular sludge. In UASB reactors fed with acetate-containing media (3 g of chemical oxygen demand [COD] per liter, corresponding to 47 mM acetate) approximately 50 days was needed at 70 degrees C and less than 15 days was needed at 55 degrees C to achieve an effluent COD of 500 to 700 mg/liter. In the UASB reactors at both 70 and 55 degrees C up to 90% of the COD was removed. Batch assays showed that sludges from two 70 degrees C UASB reactors, one run at a low effluent acetate concentration and the other run at a high effluent acetate concentration, exhibited slightly different responses to temperatures in the range from 37 to 70 degrees C. Both 70 degrees C sludges, as well as the 55 degrees C sludge, produced methane at temperatures of 37 to 73 degrees C. The 55 degrees C sludge exhibited shorter lag phases than the 70 degrees C sludges and higher specific methane production rates between 37 and 65 degrees C.     

Ammonia–methane two-stage anaerobic digestion of dehydrated waste-activated sludge

The study investigated methane production from dehydrated waste-activated sludge (DWAS) with approximately 80% water content under thermophilic conditions. The repeated batch-wise treatment of DWAS using methanogenic sludge unacclimated to high concentrations of ammonia, increased the ammonia production up to 7,600 mg N per kilogram total wet sludge of total ammonia concentration, and stopped the methane production. Investigation revealed that the loading ratio of DWAS for methanogenic sludge influences anaerobic digestion. Methane production significantly decreased and ammonia concentration increased with the increase in loading ratio of DWAS. Since the semicontinuous culture revealed that approximately 50% of organic nitrogen in DWAS converted to ammonia at sludge retention time (SRT) after 4 days at 37 degrees C and 1.33 days at 55 degrees C, the previous stripping of the ammonia produced from DWAS was carried out. The stripping of ammonia increased methane production significantly. This ammonia-methane two-stage anaerobic digestion demonstrated a successful methane production at SRT 20 days in the semicontinuous operation using a laboratory-scale reactor system.     

Vitrification of ECV304 cell suspensions using solutions containing propane-1,2-diol and trehalose

In this paper, we report on the suitability of solutions containing propane-1,2-diol (propylene glycol, PD), sugars, and salts for the vitrification of the human cell line, ECV304. Cooling (at 10 degrees C/min) and rewarming (at 80 degrees C/min) were at rates that are practicable for the tissues to be studied later. Under these conditions, 45% PD in phosphate-buffered saline (PBS) sometimes froze during cooling and always devitrified during rewarming but both events were avoided if the PBS salts were replaced by an osmotically equivalent concentration of sucrose or trehalose. The effect of such solutions on cells was evaluated using a cell culture assay in which the number of cells recovered after 3 days of culture was divided by the number cells plated, giving a cell multiplication factor or CMF. In the absence of PD the cells tolerated a low-salt concentration in solutions that were made isotonic with sugars, but they recovered poorly when 45% PD was also present. Trehalose gave significantly better recovery than sucrose. When 39% PD and 15% trehalose were included in a low-salt vehicle solution (LSV) that contained approximately 5% of the total salt concentration of PBS (this solution was designated LSV/39/15), the cells exhibited approximately 40% of untreated control CMF following exposure for 9min. LSV/39/15 vitrifies with a glass transition temperature of -102 degrees C, does not devitrify when warmed at 80 degrees C/min, and has suitable dielectric properties for uniform and rapid dielectric heating. An improved method for adding and removing LSV/39/15 gave a CMF of approximately 55% of untreated controls. Using this method, 1.0ml suspensions of ECV304 cells was cooled to, and stored briefly at, -120 degrees C and then rewarmed by immersion in a 37 degrees C water bath ( approximately 75 degrees C/min). The CMF of the cooled samples was similar to that of the exposure-only controls, approximately 50% of the untreated control CMF in both cases.     

Detailed study of anaerobic digestion of Spirulina maxima algal biomass

Biomass of the blue-green alga Spirulina maxima was converted to methane using continuous stirred tank digesters with an energy conversion efficiency of 59%. Digesters were operated using once-a-day feeding with a retention time (theta) between 5 and 40 days, volatile solid concentrations (S(to)) between 20 and 100 kg VS/m(3), and temperatures between 15 and 52 degrees C. The results indicated a maximum methane yield of 0.35 m(3) (STP)/kg VS added at theta 30 days and S(to) 20 kg VS/m(3). Under such conditions, the energy conversion of the algal biomass to methane was 59%. The maximum methane production rate of 0.80 m(3) (STP)/m(3) day was obtained with theta= 20 days and S = 100 kg VS/m(3). The mesophilic condition at 35 degrees C produced the maximum methane yield and production rate. The process was stable and characterized by a high production of volatile acids (up to 23, 200 mg/L), alkalinity (up to 20, 000 mg/L), and ammonia (up to 7000 mg/L), and the high protein content of the biomass produced a well buffered environment which reduced inhibitory effects. At higher loading rates, the inhibition of methanogenic bacteria was observed, but there was no clear-cut evidence that such a phenomenon was due to nonionized volatile acids or gaseous ammonia. The kinetic analysis using the model proposed by Chen and Hashimoto indicated that the minimum retention time was seven days. The optimum retention time increased gradually from 11 to 16 days with an increase in the initial volatile solid concentration. The kinetic constant K decreased with the improvement in the digester performance and increased in parallel with the ammonia concentration in the culture media.     

温度对谷胱甘肽分批发酵的影响及动力学模型

研究了24～32℃范围内产朊假丝酵母生产谷胱甘肽的分批发酵过程,发现较高温度对细胞生长有促进作用,而较低温度则更有利于谷胱甘肽产量的提高。应用改进的Logistic和LuedekingPiret方程分别对细胞生长动力学和谷胱甘肽合成动力学进行了模拟,得到不同温度下各种动力学参数。在此基础上,进一步研究了温度同细胞生长动力学参数之间的内在联系,得到谷胱甘肽分批发酵过程中细胞浓度的变化同温度以及底物浓度之间的一般关系式：dX-dt＝［0.0224(T+1.7)］2X(1-X/X_max)1+S｛8.26×10.6×exp［-31477/R/(T+273)］｝。验证实验结果表明,该模型具有很好的适用性。     

Control of sweating during the human menstrual cycle

Thermoregulatory responses were studied in seven women during two separate experimental protocols in the follicular (F, days 4-7) phase and during the luteal (L, days 19-22) phase of the menstrual cycle. Continuous measurements of esophageal temperature (Tes), mean skin temperature (Tsk), oxygen uptake and forearm sweating (ms) were made during all experiments. Protocol I involved both passive heat exposure (3 h) and cycle exercise at approximately 80% VO2 peak during which the environmental chamber was controlled at Ta = 50.0 degrees C, rh = 14% (Pw = 1.7 kPa). In protocol II subjects were tested during thirty-five minutes of exercise at approximately 85% VO2 peak at Ta = 35 degrees C and rh = 25% (Pw = 1.4 kPa). The normal L increase in resting Tes (approximately 0.3 degrees C) occurred in all seven subjects. Tsk was higher during L than F in all experiments conducted at 50 degrees C. During exercise and passive heat exposure, the Tes threshold for sweating was higher in L, with no change in the thermosensitivity (slope) of ms to Tes between menstrual cycle phases. This rightward or upward shift in Tes threshold for initiation of sweating averaged 0.5 degrees C for all experiments. The data indicate the luteal phase modulation in the control of sweating in healthy women is also apparent during severe exercise and/or heat stress.     

Characteristics of degraded cellulose obtained from steam-exploded wheat straw

The isolation of cellulose from wheat straw was studied using a two-stage process based on steam explosion pre-treatment followed by alkaline peroxide post-treatment. Straw was steamed at 200 degrees C, 15 bar for 10 and 33 min, and 220 degrees C, 22 bar for 3, 5 and 8 min with a solid to liquid ratio of 2:1 (w/w) and 220 degrees C, 22 bar for 5 min with a solid to liquid ratio of 10:1, respectively. The steamed straw was washed with hot water to yield a solution rich in hemicelluloses-derived mono- and oligosaccharides and gave 61.3%, 60.2%, 66.2%, 63.1%, 60.3% and 61.3% of the straw residue, respectively. The washed fibre was delignified and bleached by 2% H2O2 at 50 degrees C for 5 h under pH 11.5, which yielded 34.9%, 32.6%, 40.0%, 36.9%, 30.9% and 36.1% (% dry wheat straw) of the cellulose preparation, respectively. The optimum cellulose yield (40.0%) was obtained when the steam explosion pre-treatment was performed at 220 degrees C, 22 bar for 3 min with a solid to liquid ratio of 2:1, in which the cellulose fraction obtained had a viscosity average degree of polymerisation of 587 and contained 14.6% hemicelluloses and 1.2% klason lignin. The steam explosion pre-treatment led to a significant loss in hemicelluloses and alkaline peroxide post-treatment resulted in substantial dissolution of lignin and an increase in cellulose crystallinity. The six isolated cellulose samples were further characterised by FT-IR and 13C-CP/MAS NMR spectroscopy and thermal analysis.     

Turnover of cytochrome C in skeletal muscle of green sunfish (Lepomis cyanellus, R.) during thermal acclimation.

The concentration of cytochrome c in the skeletal muscle of the green sunfish (Lepomis cyanellus) increases with decreasing temperature of acclimation: 1.51 +/- 0.09, 1.17 +/- 0.03, and 0.98 +/- 0.07 nanomoles per gram wet weight from muscle of animals acclimated to 5 degrees, 15 degrees, and 25 degrees C, respectively. The roles of synthesis and degradation of cytochrome c during thermal acclimation were investigated by measurement of loss of specific radioactivity from cytochrome c and from total mitochondrial heme protein, and by analysis of the rate of change in concentration of cytochrome c. The radioisotope used was 14C-delta-aminolevulinic acid, a non-reutilizable heme precursor. At 25 degrees C, the half-life of cytochrome c was 7.1 days based on radioactivity measurements and 5.6 days based on change in concentration. Statistical analysis showed no significant difference in half-lives obtained by the two methods. The half-life of total mitochondrial heme protein was determined to be 5.7 days on the basis of radioactivity data, under the same conditions. No significant difference was found between the rate of turnover of the heme protein pool from mitochondria and either measurement for cytochrome c at 25 degrees C. At an acclimation temperature of 5 degrees C, the half-life of cytochrome c from skeletal muscle was 13.7 days based upon changes in concentration. At low acclimation temperature, radioactive label was retained in acid-soluble form by fish for many days, precluding measurement of half-life by this technique. Transfer of fish from 25 degrees to 5 degrees C resulted in a rapid decrease of approximately 40% in rates in synthesis of skeletal muscle cytochrome c, and a concomitant decrease in the degradation rate constant for this molecule of approximately 60%. The disproportionality in temperature-sensitivities of these two processes leads to an approximately 50% net increase in the concentration of cytochrome c during acclimation. In transfer from 5 degrees to 25 degrees C, the converse, rapid readjustments in synthetic and degradative parameters occur, resulting in the observed decrease in cytochrome c content.     

以纸为碳源去除地下水硝酸盐的研究

研究了以纸为碳源和反应介质的生物反应器对水中硝酸盐的去除。结果表明,以纸为碳源的反应器启动快．反硝化反应受温度及水力停留时间影响大。25℃的反硝化速率是14℃的1．7倍。在室温25±1℃,进水硝酸盐氮浓度为45．2mg·L^-1、水力停留时间8．6h时,反应器对硝酸盐氮的去除率在99．6％以上,当水力停留时间为7．2h,氮去除率只有50％。反硝化反应受pH值和溶解氧的影响小,反应进行过程中,纸表面形成了生物膜,纸也被消耗了．采用反应器出水再经活性炭吸附的工艺流程处理高硝酸盐氮地下水,<33．9mg·L^-1的硝酸盐氮完全去除,没有出现NC2-N,最终出水水质DOC<11mg·L^-1。     

蜜环菌胞外漆酶的合成、纯化及性质研究

研究了蜜环菌胞外漆酶合成条件和酶学性质。实验表明,培养基初始pH5.5、培养温度25℃有利于菌株产酶;与麦芽糖、山梨糖和半乳糖相比,纤维二糖和棉子糖作为碳源时漆酶产量更高;有机氮源比无机氮源有利于漆酶合成。泥炭提取液可显著诱导漆酶生成,当其含量为50%时,菌株漆酶最高产量是对照组的7倍。在蜜环菌发酵上清液中检测到3个漆酶同功酶组分,其主要活性（约占75%）组份漆酶A经 (NH₄)₂SO₄沉淀、制备级PAGE电泳和阴离子交换柱层析被分离纯化至电泳均一,SDSPAGE法测得酶亚基分子量59kD,凝胶过滤色谱法测定活性酶分子量58kD。纯化的漆酶A等电点pI为4.0,氧化愈创木酚的最适反应pH为5.6,最适温度为60℃,在60℃和65℃时半衰期分别为45min和36.8min,在pH5.2～7.2范围内稳定性较好。100mmol/L Cl^-对该酶有显著抑制作用,1mmol/L SO^2-₄ 对漆酶有激活作用,1mmol/L NaN₃可完全抑制酶活性,10 mmol/L EDTA对漆酶活没有明显影响,1mmol/L Cu²⁺对漆酶有激活作用。以愈创木酚为底物时,测得酶的K_m=1.026mmol/L,V_max=5μmol/(min·mg);以ABTS为底物时,测得其K_m=0.22mmol/L,V_max=69μmol/(min·mg)。     

Application of a cell-once-through perfusion strategy for production of recombinant antibody from rCHO cells in a Centritech Lab II centrifuge system

Based upon the results of scale-down intermittent perfusion processes, a cell-once-through (COT) perfusion concept was applied to a dual bioreactor system coupled to a Centritech Lab II centrifuge for culture of recombinant Chinese hamster ovary (rCHO) cells for monoclonal antibody production. In this new culture mode, i.e., the COT perfusion process, total spent medium was transferred to the centrifuge and a fixed percentage was removed. Approximately 99% of the viable cells are transferred to another bioreactor filled with fresh medium by single operation of the Centritech Lab II centrifuge system for about 30 min. Accordingly, a significant reduction of the cell-passage frequency to the centrifuge led to minimization of cell damage caused by mechanical shear stress, oxygen limitation, nutrient limitation, and low temperature outside the bioreactor. The effects of culture temperature shift and fortified medium on cell growth and recombinant antibody production in the COT perfusion process were investigated. Although the suppressive effects of low culture temperature on cell growth led to a loss of stability in a long-term COT perfusion culture system, the average antibody concentration at 33 degrees C was 157.8 mg/L, approximately 2.4-fold higher than that at 37 degrees C. By the use of a fortified medium at 37 degrees C, rCHO cells were maintained at high density above 1.2 x 10(7) cells/mL, and antibody was produced continuously in a range of 260-280 mg/L in a stable long-term COT perfusion culture. The proposed new culture mode, the COT perfusion approach, guarantees the recovery of rCHO cells damaged by lowered temperature or high lactate and ammonium concentration. It will be an attractive choice for minimization of cell damage and stable long-term antibody production with high cell density.     

Thermophilic biodegradation of BTEX by two Thermus Species

Two thermophilic bacteria, Thermus aquaticus ATCC 25104 and Thermus species ATCC 27978, were investigated for their abilities to degrade BTEX (benzene, toluene, ethylbenzene, and xylenes). Thermus aquaticus and the Thermus sp. were grown in a nominal medium at 70 degrees C and 60 degrees C, respectively, and resting cell suspensions were used to study BTEX biodegradation at the same corresponding temperatures. The degradation of BTEX by these cell suspensions was measured in sealed serum bottles against controls that also displayed significant abiotic removals of BTEX under such high-temperature conditions. For T. aquaticus at a suspension density of only 1.3 x 10(7) cells/mL and an aqueous total BTEX concentration of 2.04 mg/L (0.022 mM), benzene, toluene, ethylbenzene, m-xylene, and an unresolved mixture of o-and p-xylenes were biodegraded by 10, 12, 18, 20, and 20%, respectively, after 45 days of incubation at 70 degrees C. For the Thermus sp. at a suspension density of 1.1 x 10(7) cells/mL and an aqueous total BTEX concentration of 6.98 mg/L (0.079 mM), benzene, toluene, ethylbenzene, m-xylene, and the unresolved mixture of o-and p-xylenes were biodegraded by 40, 35, 32, 33, and 33%, respectively, after 45 days of incubation at 60 degrees C. Raising the BTEX concentrations lowered the extents of biodegradation. The biodegradations of both benzene and toluene were enhanced when T. aquaticus and the Thermus sp. were pregrown on catechol and o-cresol, respectively, as carbon sources. Use of [U-(14)C]benzene and [ring-(14)C]toluene verified that a small fraction of these two compounds was metabolized within 7 days to water-soluble products and CO(2) by these nongrowing cell suspensions. Our investigation also revealed that the nominal medium can be simplified by eliminating the yeast extract and using a higher tryptone concentration (0.2%) without affecting the growth and BTEX degrading activities of these cells. (c) 1995 John Wiley & Sons, Inc.     

Temperature preference and respiration of acaridid mites

The thermal preferences in a grain mass and respiration at various temperatures in mites (Acari: Acarididae) of medical and economical importance [Acarus siro (L. 1758), Dermatophagoides farinae Hughes 1961, Lepidoglyphus destructor (Schrank 1871), and Tyrophagus putrescentiae (Schrank 1781)] were studied under laboratory conditions. Based on the distribution of mites in wheat, Triticum aestivum L., grain along a thermal gradient from 10 to 40 degrees C, L. destructor, D. farinae, and A. siro were classified as eurythermic and T. putrescentiae as stenothermic. The lowest preferred temperature was found for D. farinae (28 degrees C), followed by A. siro (28.5 degrees C), L. destructor (29.5 degrees C), and T. putrescentiae (31.5 degrees C). The relationship between the respiration rate and the temperature was similar for all four mite species. The highest respiration was found in the range from 31 to 33 degrees C. This is approximately 2 degrees C higher than the preferred temperature of these species. The lower temperature threshold of respiration ranged from 1 to 5 degrees C and the upper threshold ranged from 45 to 48 degrees C. Acclimatization of A. siro to temperature regimes of 5, 15, and 35 degrees C resulted in thermal preferences between 9 and 12 degrees C, 9 and 20 degrees C, and 28 and 35 degrees C, respectively. The respiration rate of acclimatized specimens increased with the temperature, reaching a maximum at 29.0 degrees C for mites acclimatized at 5 and 15 degrees C and a maximum at 33.7 degrees C for those acclimatized at 30 degrees C.     

Enhancement of 2,4-dinitrotoluene biodegradation by Burkholderia sp. in sand bioreactors using bacterial hemoglobin technology

Continuous flow sand column bioreactor experiments were conducted to investigate the effect of 2,4-dinitrotoluene (DNT) concentration (i.e. DNT loading rate) and influent dissolved oxygen (DO) concentration on aerobic biodegradation of DNT by wild type (DNT) and recombinant (YV1) Burkholderia sp., the latter containing plasmid pSC160 which carries the gene (vgb) encoding the hemoglobin (VHb) from the bacterium Vitreoscilla. The experiments were conducted in two continuous flow packed bed sand column bioreactors, one growing the wild type strain and the other growing YV1. Under oxygen-rich feed conditions (6.8 mg DO/L in the feed) with an influent DNT concentration of 99.6 mg/L (DNT loading rate approximately = 9.2 mg/m2/day), the effluent DNT concentration from the wild type bioreactor reached 0.7 mg DNT/L in 40 days whereas it was less than 0.2 mg DNT/L for the YV1 bioreactor in about 25 days. When influent DNT concentration was increased to 214 mg/L (DNT loading rate approximately = 20.3 mg/m2/day) while maintaining the same influent DO level of 6.8 mg/L, the effluent DNT concentration increased to about 5 mg/L for the wild type bioreactor whereas it was maintained at less than 0.2 mg/L for the YV1 bioreactor. Additionally, when influent DO was reduced from 6.8 mg/L to 3.1 mg/L while the influent DNT concentration remained at 214 mg/L, the effluent DNT concentration increased to more than 20 mg/L for the wild type bioreactor but up to only 1.7 mg/L for the YV1 bioreactor. A subsequent increase of influent DO back to 6.6 mg/L reduced the effluent DNT concentration to about 5 mg/L for the wild type bioreactor and to 0.10-0.19 mg/L for the YV1 bioreactor. These results confirm the utility of vgb technology to enhance biodegradation of aromatic compounds under hypoxic conditions and also that this enhancement can be maintained over extended periods of time as evidenced by plasmid stability in Burkholderia YV1.