Use of zero-valent iron biosand filters to reduce Escherichia coli O157:H12 in irrigation water applied to spinach plants in a field setting

Aims:  Zero‐valent iron (ZVI) filters may provide an efficient method to mitigate the contamination of produce crops through irrigation water. Methods:  A field‐scale system was utilized to evaluate the effectiveness of a biosand filter (S), a biosand filter with ZVI incorporated (ZVI) and a control (C, no treatment) in decontaminating irrigation water. An inoculum of c. 8·5 log CFU 100 ml^?1 of Escherichia coli O157:H12 was introduced to all three column treatments in 20‐l doses. Filtered waters were subsequently overhead irrigated to ‘Tyee’ spinach plants. Water, spinach plant and soil samples were obtained on days 0, 1, 4, 6, 8, 10, 13 and 15 and analysed for E. coli O157:H12 populations. Results:  ZVI filters inactivated c. 6 log CFU 100 ml^?1E. coli O157:H12 during filtration on day 0, significantly (P < 0·05) more than S filter (0·49 CFU 100 ml^?1) when compared to control on day 0 (8·3 log CFU 100 ml^?1). On day 0, spinach plants irrigated with ZVI‐filtered water had significantly lower E. coli O157 counts (0·13 log CFU g^?1) than spinach irrigated with either S‐filtered (4·37 log CFU g^?1) or control (5·23 log CFU g^?1) water. Soils irrigated with ZVI‐filtered water contained E. coli O157:H12 populations below the detection limit (2 log CFU g^?1), while those irrigated with S‐filtered water (3·56 log CFU g^?1) were significantly lower than those irrigated with control (4·64 log CFU g^?1). Conclusions:  ZVI biosand filters were more effective in reducing E. coli O157:H12 populations in irrigation water than sand filters. Significance and Impact of the Study:  Zero‐valent ion treatment may be a cost‐effective mitigation step to help small farmers reduce risk of foodborne E. coli infections associated with contamination of leafy greens.     

Multiple pathways of charge recombination revealed by the temperature dependence of electron transfer kinetics in cyanobacterial photosystem I

The kinetics of charge recombination in Photosystem I P₇₀₀-F_A/F_B complexes and P₇₀₀-F_X cores lacking the terminal iron?sulfur clusters were studied over a temperatures range of 310 K to 4.2 K. Analysis of the charge recombination kinetics in this temperature range allowed the assignment of backward electron transfer from the different electron acceptors to P₇₀₀⁺. The kinetic and thermodynamic parameters of these recombination reactions were determined. The kinetics of all electron transfer reactions were activation-less below 170 K, the glass transition temperature of the water-glycerol solution. Above this temperature, recombination from [F_A/F_B]^? in P₇₀₀-F_A/F_B complexes was found to proceed along two pathways with different activation energies (E_a). The charge recombination via A_1A has an E_a of ~290 meV and is dominant at temperatures above ~280 K, whereas the direct recombination from F_X^? has an E_a of 22 meV and is prevalent in the 200 K to 270 K temperature range. Charge recombination from the F_X cluster becomes highly heterogeneous at temperatures below 200 K. The conformational mobility of Photosystem I was studied by molecular dynamics simulations. The F_X cluster was found to ‘swing’ by ~30° along the axis between the two sulfur atoms proximal to F_A/F_B. The partial rotation of F_X is accompanied by significant changes of electric potential within the iron?sulfur cluster, which may induce preferential electron localization at different atoms of the F_X cluster. These effects may account for the partial arrest of forward electron transfer and for the heterogeneity of charge recombination observed at the glass transition temperature.     

Thermodynamic analysis of the physical state of water during freezing in plant tissue, based on the temperature dependence of proton spin-spin relaxation

Multi-proton spin-echo images were collected from cold-acclimated winter wheat crowns (Triticum aestivum L.) cv. Cappelle Desprez at 400 MHz between 4 and ?4 °C. Water proton relaxation by the spin-spin (T2) mechanism from individual voxels in image slices was found to be mono-exponential. The temperature dependence of these relaxation rates was found to obey Arrhenius or absolute rate theory expressions relating temperature, activation energies and relaxation rates, Images whose contrast is proportional to the Arrhenius activation energy (E_a), Gibb's free energy of activation (ΔG^?), and the entropy of activation (ΔS^?) for water relaxation on a voxel basis were constructed by post-image processing. These new images exhibit contrast based on activation energies rather than rules of proton relaxation. The temperature dependence of water proton T₂ relaxation rates permits prediction of changes in the physical state of water in this tissue over modest temperature ranges. A simple model is proposed to predict the freezing temperature kof various tissue in wheat crowns. The average E_a and ΔH^? for water proton T₂ relaxation over the above temperature range in winter wheat tissue were ?6.4 ± 14.8 and ?8.6 ± 14.8kj mol^?1, respectively. This barrier is considerably lower than the E_a for proton translation in ice at 0°C, which is reported to be between 46.0 and 56.5 kj mol^?1     

EFFECTS OF LIGHT AND TEMPERATURE ON GROWTH,NITRATE UPTAKE,AND TOXIN PRODUCTION OF TWO TROPICAL DINOFLAGELLATES: ALEXANDRIUM TAMIYAVANICHII AND ALEXANDRIUM MINUTUM (DINOPHYCEAE)1

The two tropical estuarine dinoflagellates, Alexandrium tamiyavanichii Balech and A. minutum Halim, were used to determine the ecophysiological adaptations in relation to their temperate counterparts. These species are the two main causative organisms responsible for the incidence of paralytic shellfish poisoning (PSP) in Southeast Asia. The effects of light (10, 40, 60, and 100 μmol photons·m^?2·s^?1) and temperature (15, 20, and 25°C) on the growth, nitrate assimilation, and PST production of these species were investigated in clonal batch cultures over the growth cycle. The growth rates of A. tamiyavanichii and A. minutum increased with increasing temperature and irradiance. The growth of A. tamiyavanichii was depressed at lower temperature (20°C) and irradiance (40 μmol photons·m^?2·s^?1). Both species showed no net growth at 10 μmol photons·m^?2·s^?1 and a temperature of 15°C, although cells remained alive. Cellular toxin quotas (Q_t) of A. tamiyavanichii and A. minutum varied in the range of 60–180 and 10–42 fmol PST·cell^?1, respectively. Toxin production rate, R_tox, increased with elevated light at both 20 and 25°C, with a pronounced effect observed at exponential phase in both species (A. tamiyavanichii, r²=0.95; A. minutum, r²=0.96). Toxin production rate also increased significantly with elevated temperature (P<0.05) for both species examined. We suggest that the ecotypic variations in growth adaptations and toxin production of these Malaysian strains may reveal a unique physiological adaptation of tropical Alexandrium species.     

Behavioural response of larval Atlantic menhaden to different rates of temperature change

Larval Atlantic menhaden Brevoortia tyrannus, spawned off North Carolina (U.S.A.) during the winter, undergo cross-shelf transport from the western Gulf Stream edge to coastal bays and estuaries. Variation in water flow direction with depth provides larvae the opportunity to enhance shoreward transport, if they can regulate their depth behaviourally. Temperature, which normally decreases with depth on the continental shelf, is one possible cue for depth regulation. Laboratory-reared larval menhaden of two different ages were exposed to varying relative rates of temperature increases and decreases, which were presented from both above and below the larvae. Temperature decreases from below caused an ascent response in both young and old larvae, but neither responded to this cue from above. The minimum (threshold) relative rates of decrease for initiating ascents were similar (7.9 × 10^?2, 10.7 × 10^?2° C min^?1) for both age larvae as were the minimum absolute amounts of decrease that must occur before a response (0.1, 0.05°C). Young larvae did not respond to a temperature increase, while old larvae ascended regardless of whether the increase was presented from above or below. Threshold relative rates of increase were 8.59 × 10^?2°C min^?1 from below and 14.79 × 10^?2° C min^?1 from above. The threshold rates and range of larval speeds during vertical movements were used to calculate vertical temperature gradients that could be perceived. These values were compared to measured gradients in areas inhabited by menhaden larvae. On the continental shelf, detectable temperature gradients appear common for temperature decreases that would occur upon descending and temperature increases upon ascending. However, it is uncommon for larvae to encounter temperature increases upon descending that would initiate an ascent response. These results support the hypothesis that menhaden larvae are capable of using temperature gradients for depth regulation.     

PRIMARY PRODUCTION OF CRUSTOSE CORALLINE RED ALGAE IN A HIGH ARCTIC FJORD1

Crustose coralline algae occupied ～1%–2% (occasionally up to 7%) of the sea floor within their depth range of 15–50 m, and they were the dominant encrusting organisms and macroalgae beyond 20 m depth in Young Sound, NE Greenland. In the laboratory, oxygen microelectrodes were used to measure net photosynthesis (P) versus downwelling irradiance (E_d) and season for the two dominant corallines [Phymatolithon foecundum (Kjellman) Düwel et Wegeberg 1996 and Phymatolithon tenue (Rosenvinge) Düwel et Wegeberg 1996] representing> 90% of coralline cover. Differences in P‐E_d curves between the two species, the ice‐covered and open‐water seasons, or between specimens from 17 and 36 m depth were insignificant. The corallines were low light adapted, with compensation irradiances (E_c) averaging 0.7–1.8 μmol photons·m ^{? 2}·s ^{? 1} and light adaptation (E_k) indices averaging 7–17 μmol photons·m ^{? 2}·s ^{? 1}. Slight photoinhibition was evident in most plants at irradiances up to 160 μmol photons·m ^{? 2}·s ^{? 1}. Photosynthetic capacity (P_m) was low, averaging 43–67 mmol O₂·m ^{? 2} thallus·d ^{? 1} (～250–400 g C·m ^{? 2} thallus·yr ^{? 1}). Dark respiration rates averaged ～5 mmol O₂·m ^{? 2} thallus·d ^{? 1}. In ice covered periods, E_d at 20 m depth averaged ～1 μmol photons·m ^{? 2}·s ^{? 1}, with daily maxima of 2–3 μmol photons·m ^{? 2}·s ^{? 1}. During the open water season, E_d at 20 m depth averaged ～7 μmol photons·m ^{? 2}·s ^{? 1} with daily maxima of ～30 μmol photons·m ^{? 2}·s ^{? 1}. Significant net primary production of corallines was apparently limited to the 2–3 months with open water, and the small contribution of corallines to primary production seems due to low P_m values, low in situ irradiance, and their relatively low abundance in Young Sound.     

Discontinuities in the Temperature Function of Transmembrane Water Transport in Chara: Relation to Ion Transport

The NMR (nuclear magnetic resonance) method of Conlon and Outhred (1972) was used to measure diffusional water permeability of the nodal cells of the green alga Chara gymnophylla. Two local minima at 15 and 30°C of diffusional water permeability (P _d ) were observed delimiting a region of low activation energy (E _a around 20 kJ/mol) indicative of an optimal temperature region for membrane transport processes. Above and below this region water transport was of a different type with high E _a (about 70 kJ/mol). The triphasic temperature dependence of the water transport suggested a channel-mediated transport at 15–30°C and lipid matrix-mediated transport beyond this region. The K⁺ channel inhibitor, tetraethylammonium as well as the Cl⁻ channel inhibitor, ethacrynic acid, diminished P _d in the intermediate temperature region by 54 and 40%, respectively. The sulfhydryl agent p-(chloromercuri-benzensulfonate) the water transport inhibitor in erythrocytes also known to affect K⁺ transport in Chara, only increased P _d below 15°C. In high external potassium (`K-state') water transport minima were pronounced. The role of K⁺ channels as sensors of the optimal temperature limits was further emphasized by showing a similar triphasic temperature dependence of the conductance of a single K⁺ channel also known to cotransport water, which originated from cytoplasmic droplets (putatively tonoplast) of C. gymnophylla. The minimum of K⁺ single channel conductance at around 15°C, unlike the one at 30°C, was sensitive to changes of growth temperature underlining membrane lipid involvement. The additional role of intracellular (membrane?) water in the generation of discontinuities in the above thermal functions was suggested by an Arrhenius plot of the cellular water relaxation rate which showed breaks at 13 and 29°C. Received: 12 August 1998/Revised: 13 November 1998     

Leaf temperature effects on gas exchange in Quercus ilex L. growing under field conditions

ABSTRACT

Gas exchange temperature dependence in Quercus ilex shrubs growing in the Mediterranean maquis was analysed. The gas exchange trend was monitored during the year: photosynthetic activity (A _net) reached the highest average rates in early spring and autumn (12.5 µmol m^-2s^-1 was the absolute maximum A _net measured) and the lowest rates were monitored in the middle of June. There was a good correlation (r = 0.72) between A _net and g _s (A _net = 4.1246 ln g _s + 4316; P < 0.01), indicating that stomatal control of CO₂ diffusion plays an important role in controlling photosynthetic activity. Leaf temperature allowing the highest photosynthetic and stomatal conductance rates of Quercus ilex were in the range 17.5 – 29°C. A _net and g_s dropped below half its maximum value when leaf temperatures were below 11.5°C and above 35.7°C. Transpiration rates (E) were strongly related to leaf temperature; E increased as leaf temperature increased and the highest E rates were monitored in June, despite a 46% decrease in g _s. Leaf water loss from transpiration, during the drought period, could result in leaf water stress which would exacerbate heat effects on photosynthesis. During summer, the increase in leaf temperatures decreased g _s which in turn decreased A _net. Consequently, stomatal control in Quercus ilex may be considered as an adaptive strategy during drought.     

PHOTOSYNTHESIS IN AN EXTREME SHADE ENVIRONMENT: BENTHIC MICROBIAL MATS FROM LAKE HOARE, A PERMANENTLY ICE-COVERED ANTARCTIC LAKE

We investigated the composition of benthic microbial mats in permanently ice-covered Lake Hoare, Antarctica, and their irradiance vs. photosynthetic oxygen exchange relationships. Mats could be subdivided into three distinct depth zones: a seasonally ice-free “moat” zone and two under-ice zones. The upper under-ice zone extended from below the 3.5 m thick ice to approximately 13 m and the lower from below 13 m to 22 m. Moat mats were acclimated to the high irradiance they experienced during summer. They contained photoprotective pigments, predominantly those characteristic of cyanobacteria, and had high compensation and saturating irradiances (E_c and E_k) of 75 and 130 μmol photons·m⁻²·s⁻¹, respectively. The moat mats used light inefficiently. The upper under-ice community contained both cyanobacteria and diatoms. Within this zone, biomass (as pigments) increased with increasing depth, reaching a maximum at 10 m. Phycoerythrin was abundant in this zone, with shade acclimation and efficiency of utilization of incident light increasing with depth to a maximum of 0.06 mol C fixed·mol⁻¹ incident photons under light-limiting conditions. Precipitation of inorganic carbon as calcite was associated with this community, representing up to 50% of the carbon sequestered into the sediment. The lower under-ice zone was characterized by a decline in pigment concentrations with depth and an increasing prevalence of diatoms. Photosynthesis in this community was highly shade acclimated and efficient, with E_c and E_k below 0.5 μmol·m⁻²·s⁻¹ and 2 μmol·m⁻²·s⁻¹, respectively, and maximum yields of 0.04 mol C fixed·mol⁻¹ incident quanta. Carbon uptake in situ by both under-ice and moat mats was estimated at up to 100 and 140 mg·m⁻²·day⁻¹, based on the photosynthesis–irradiance curves, incident irradiance, and light attenuation by ice and the water column.     

PRODUCTIVITY OF THE FILAMENTOUS ALGA PITHOPHORA OEDOGONIA (CHLOROPHYTA) IN SURREY LAKE,INDIANA1

Biomass, akinete numbers, net photosynthesis, and respiration of Pithophora oedogonia were monitored over two growing seasons in shallow Surrey Lake, Indiana. Low rates of photosynthesis occurred from late fall to early spring and increased to maximum levels in late spring to summer (29–39 mgO₂·g^?1 dry wt·h^?1). Areal biomass increased following the rise in photosynthesis and peaked in autumn (163–206g dry wt·m^?2). Photosynthetic rates were directly correlated with temperature, nitrogen, and phosphorus over the entire annual cycle and during the growing season. Differences in photosynthetic activity and biomass between the two growing seasons (1980 and 1981) were apparently related to higher, early spring temperatures and higher levels of NO₃-N and PO₄-P in 1981. Laboratory investigations of temperature and light effects on Pithophora photosynthesis and respiration indicated that these processes were severely inhibited below 15°C. The highest P_max value occurred at 35°C (0.602 μmol O₂·mg^?1 chl a·min^?1). Rates of dark respiration did not increase above 25°C thus contributing to a favorable balance of photosynthetic production to respiratory utilization at high temperatures. Light was most efficiently utilized at 15°C as indicated by minimum values of I_k(47 μE·m^?2·s^?1) and I_c (6 μE·m^?2·s^?1). Comparison of P. oedogonia and Cladophora glomerata indicated that the former was more tolerant of temperatures above 30°C. Pithophora's tolerance of high temperature and efficient use of low light intensity appear to be adaptive to conditions found within the dense, floating algal mats and the shallow littoral areas inhabited by this filamentous alga.     

Inactivation of Bacillus cereus by Na‐chlorophyllin‐based photosensitization on the surface of packaging

Aims: This study was focused on the possibility to inactivate food‐borne pathogen Bacillus cereus by Na‐chlorophyllin (Na‐Chl)‐based photosensitization in vitro and after attachment to the surface of packaging material. Methods and Results: Bacillus cereus in vitro or attached to the packaging was incubated with Na‐Chl (7·5 × 10^?8 to 7·5 × 10^?5 mol l^?1) for 2–60 min in phosphate buffer saline. Photosensitization was performed by illuminating cells under a light with a λ of 400 nm and an energy density of 20 mW cm^?2. The illumination time varied 0–5 min and subsequently the total energy dose was 0–6 J cm^?2. The results show that B. cereus vegetative cells in vitro or attached to the surface of packaging after incubation with 7·5 × 10^?7 mol l^?1 Na‐Chl and following illumination were inactivated by 7 log. The photoinactivation of B. cereus spores in vitro by 4 log required higher (7·5 × 10^?6 mol l^?1) Na‐Chl concentration. Decontamination of packaging material from attached spores by photosensitization reached 5 log at 7·5 × 10^?5 mol l^?1 Na‐Chl concentration. Comparative analysis of different packaging decontamination treatments indicates that washing with water can diminish pathogen population on the surface by <1 log, 100 ppm Na‐hypochlorite reduces the pathogens about 1·7 log and 200 ppm Na‐hypochlorite by 2·2 log. Meanwhile, Na‐Chl‐based photosensitization reduces bacteria on the surface by 4·2 orders of magnitude. Conclusions: Food‐borne pathogen B. cereus could be effectively inactivated (7 log) by Na‐Chl‐based photosensitization in vitro and on the surface of packaging material. Spores are more resistant than vegetative cells to photosensitization‐based inactivation. Comparison of different surface decontamination treatments indicates that Na‐Chl‐based photosensitization is much more effective antibacterial tool than washing with water or 200 ppm Na‐hypochlorite. Significance and Impact of the Study: Our data support the idea that Na‐Chl‐based photosensitization has great potential for future application as an environment‐friendly, nonthermal surface decontamination technique.     

Scaling relationships for woody tissue respiration in two tropical rain forests

The relationship between gross primary productivity (GPP) and net primary productivity (NPP) is not fully understood. One of the uncertainties relevant to this issue is the magnitude of woody tissue respiration. Although some data exist for temperate and boreal zones, measurements of woody tissue respiration in tropical forests are sparse. We made in situ chamber measurements of woody tissue respiration in two tropical rain forests, one in the Brazilian Amazon (Reserva Jarú) and one in Central Cameroon (Mbalmayo Reserve). We made measurements on a wide range of species at each site and over a range of stem diameters from 0·02 to 1·4 m. The rate of efflux of carbon dioxide (CO₂) from bark at 25 °C, R_t, varied from 0·1 to 5·2 µmol m^?2 s^?1 across the two sites, and the efflux was related to both volume and surface area components of the measured stem sections. The temperature response in R_t was slightly higher at Jarú than at Mbalmayo, with Q₁₀ values of 1·8 (± 0·1 SE) and 1·6 (± 0·1 SE), respectively. A log–log regression showed that R_t was significantly related to stem diameter, D (P < 0·001; r² = 0·58–0·62) and was significantly higher at Mbalmayo than at Jarú (P < 0·001), but that the rate of increase in R_t with stem diameter, D, was similar between sites. At the Mbalmayo site, tree growth measurements made over a 4 month period were used to make two estimates of the maintenance (R_m) and construction (R_c) components of respiration embedded in R_t. The two methods agreed closely, suggesting that R_m was approximately 80% of R_c at this site. R_m could be strongly related to D using a sigmoidal relationship that described both surface area and volume components as sources of respiratory CO₂ (r² = 0·71). This functional model was combined with inventory, growth and climate data for the Mbalmayo site to make a first estimate of annual above‐ground woody tissue respiration, R_A, which was 257 (± 18 SE) g C m^?2 year^?1. This value corresponds to approximately 10% of GPP, slightly lower than that found for another tropical rain forest, but higher than for temperate forests. When combined with data from six other sites in tropical, temperate and boreal settings, a very strong relationship was found between R_A and leaf area index (LAI), and between R_A/GPP and LAI (P < 0·001, r² = 0·98). This indicates that R_A exerts an appreciable constraint on NPP and that this constraint varies closely with LAI across widely differing types of woody vegetation.     

Thermodynamics of partitioning and efflux of phenothiazines from liposomes

Summary The partitioning of nine phenothiazines between dimyristoylphosphatidylcholine (DMPC) liposomes and 0.9% wt/vol saline at pH 6 has been studied both below and above the phase transition temperature (T _c ) of the phospholipid. Higher partitioning was observed aboveT _c . Both the entropy and enthalpy of partitioning were positive below and aboveT _c , and a linear relationship between the entropy and enthalpy has been derived. In general, the partitioning and transport of alkylaminophenothiazines in DMPC liposomes over the temperature range of 5 to 40°C is entropically controlled. The entropies and enthalpies of partitioning of various groups in the phenothiazine structure have been calculated.No relationship was found between particle size of the DMPC liposomes and the equilibrium partition coefficient at 25°C. However, the particle size of liposomes did increase with increasing acyl chain length of the phospholipid.Using differential scanning calorimetry, the enthalpy and entropy of transition of the DMPC liposomes in the absence and presence of phenothiazines has been calculated. The temperature dependence of the first-order rate constant of trimeprazine tartrate transport in DMPC liposomes was investigated and was found to be maximum at theT _c of the phospholipid.     

Temperature dependence of anion transport in the human red blood cell

Arrhenius plots of chloride and bromide transport yield two regions with different activation energies (E_a). Below 15 or 25°C (for Cl⁻ and Br⁻, respectively), E_a is about 32.5 kcal/mol; above these temperatures, about 22.5 kcal/mol (Brahm, J. (1977) J. Gen. Physiol. 70, 283–306). For the temperature dependence of SO₄²⁻ transport up to 37°C, no such break could be observed. We were able to show that the temperature coefficient for the rate of SO₄²⁻ transport is higher than that for the rate of denaturation of the band 3 protein (as measured by NMR) or the destruction of the permeability barrier in the red cell membrane. It was possible, therefore, to extend the range of flux measurements up to 60°C and to show that, even for the slowly permeating SO₄²⁻ in the Arrhenius plot, there appears a break, which is located somewhere between 30 and 37°C and where E_a changes from 32.5 to 24.1 kcal/mol. At the break, the turnover number is approx. 6.9 ions/band 3 per s. Using ³⁵Cl⁻-NMR (Falke, Pace and Chan (1984) J. Biol. Chem. 259, 6472–6480), we also determined the temperature dependence of Cl⁻-binding. We found no significant change over the entire range from 0 to 57°C, regardless of whether the measurements were performed in the absence or presence of competing SO₄²⁻. We conclude that the enthalpy changes associated with Cl⁻-or SO₄²⁻-binding are negligible as compared to the E_a values observed. It was possible, therefore, to calculate the thermodynamic parameters defined by transition-state theory for the transition of the anion-loaded transport protein to the activated state for Cl⁻, Br⁻ and SO₄²⁻ below and above the temperatures at which the breaks in the Arrhenius plots are seen. We found in both regions a high positive activation entropy, resulting in a low free enthalpy of activation. Thus the internal energy required for carrying the complex between anion and transport protein over the rate-limiting energy barrier is largely compensated for by an increase of randomness in the protein and/or its aqueous environment.     

Kinetics and thermodynamics of catalysis and thermal inactivation of a novel α-amylase (Tp-AmyS) from Thermotoga petrophila

Abstract

This research is focussed on kinetic, thermodynamic and thermal inactivation of a novel thermostable recombinant α-amylase (Tp-AmyS) from Thermotoga petrophila. The amylase gene was cloned in pHIS-parallel1 expression vector and overexpressed in Escherichia coli. The steady-state kinetic parameters (V_max, K_m, k_cat and k_cat/K_m) for the hydrolysis of amylose (1.39?mg/min, 0.57?mg, 148.6?s^?1, 260.7), amylopectin (2.3?mg/min, 1.09?mg, 247.1?s^?1, 226.7), soluble starch (2.67?mg/min, 2.98?mg, 284.2?s^?1, 95.4) and raw starch (2.1?mg/min, 3.6?mg, 224.7?s^?1, 61.9) were determined. The activation energy (E_a), free energy (ΔG), enthalpy (ΔH) and entropy of activation (ΔS) at 98?°C were 42.9?kJ mol^?1, 74?kJ mol^?1, 39.9?kJ mol^?1 and ?92.3 J mol^?1 K^?1, respectively, for soluble starch hydrolysis. While ΔG of substrate binding (ΔG_E-S) and ΔG of transition state binding (ΔG_E-T) were 3.38 and ?14.1?kJ mol^?1, respectively. Whereas, EaD, Gibbs free energy (ΔG*), increase in the enthalpy (ΔH*) and activation entropy (ΔS*) for activation of the unfolding of transition state were 108, 107, 105?kJ mol^?1 and ?4.1 J mol^?1 K^?1. The thermodynamics of irreversible thermal inactivation of Tp-AmyS revealed that at high temperature the process involves the aggregation of the protein.     

Stomatal and photosynthetic responses of olive (Olea europaea L.) leaves to water deficits

The leaf gas exchange of mature olive trees (Olea europaea L.) was characterized over a wide range of water deficits in the field during 1998, in Cordoba, Spain. Leaf photosynthesis (A) and stomatal conductance (g_l) responded diurnally and seasonally to variations in tree water status and evaporative demand. In the absence of water stress, A and g_l were generally high during autumn and low in days of high vapour pressure deficits (VPD). Leaf A varied between 0 and 2 µmol m^?2 s^?1 under severe water deficits that lowered the stem water potential (Ψ_x) to ?8·0 MPa, but recovered rapidly following rehydration. Transpiration efficiency (TE) was curvilinearly related to VPD and not influenced by water deficits except in cases of severe water stress, where low TE values were observed at Ψ_x below ?4 MPa. Three models of leaf conductance were calibrated and validated with the experimental data; two were based on the model proposed by Leuning (L) and the other was derived from the widely used Jarvis (J) model. The L models performed better than the J model in two validation tests. The scatter of the predictions and the limited accuracy of all three models suggest that, in addition to the physiological and environmental variables considered, there are additional endogenous factors influencing the g_l of olive leaves.     

Kinetics and thermodynamics of the P870+Q−A → P870+Q−B reaction in isolated reaction centers from the photosynthetic bacterium Rhodopseudomonas sphaeroides

The temperature dependences of the P870⁺Q^?_A → P870Q_A and P870⁺Q^?_B → P870Q_B recombination reactions were measured in reaction centers from Rhodopseudomonas sphaeroides. The data indicate that the P870⁺Q^?_B state decays by thermal repopulation of the P870⁺Q^?_A state, followed by recombination. ΔG° for the P870⁺Q^?_A → P870⁺Q^?_B reaction is ?6.89 kJ · mol^?1, while ΔH° = ?14.45 kJ · mol^?1 and ?TΔS° = + 7.53 kJ · mol^?1. The activation ethalpy, $\text{H}{}^3$, for the P870⁺Q^?_A Δ P870⁺Q^?_B reaction is +56.9 kJ · mol^?1, while the activation entropy is near zero. The results permit an estimate of the shape of the potential energy curve for the P870⁺Q^?_A → P870⁺Q^?_B electron transfer reaction.     

Thermal effects on motion and orientation of the cholestane spin label in planar multibilayers of dimyristoylphosphatidylcholine and dipalmitoylphosphatidylcholine

A detailed picture of the orientation and restricted motion of the cholestane spin label (3-spiro-doxyl-5α-cholestane) in planar multibilayers of dipalmitoylphosphatidylcholine and dimyristoylphosphatidylcholine has been recorded by simultaneous simulation of ESR spectra obtained with the magnetic field parallel and perpendicular to the bilayers (Shimoyama, Y., Eriksson, L.E.G. and Ehrenberg, A. (1978) Biochim. Biophys. Acta 508, 213–235). The analysis has been made over the temperature range ?30°C to 60°C on samples containing 20 to 22% water. At low temperatures the cholestane spin label is tilted with respect to the lipid bilayer normal by an angle of approx. 30° which disappears at the pretransition. In this low temperature range the restricted twisting motion has an activation energy of 5.5 kJ·mol^?1. Above the main transition the twisting motion is unrestricted and has the activation energy 20 kJ·mol^?1. From below the pretransition to above the main transition the velocity of the twisting motion increases by an order of magnitude. The amplitude of the wobbling motion increases abruptly from 0° to 35° at the main transition.     

Isokinetic relationships for the effect of inorganic phosphate and protons on the deoxygenation rate of human hemoglobin

The rate of hemoglobin deoxygenation is measured as a function of inorganic phosphate concentration, pH, and temperature. Isokinetic relationships (enthalpy-entropy compensation) are searched for by applying the method of O. Exner and, for comparative purposes, the conventional method of plotting the energy of activation (E*) versus the natural log of the pre-exponentional factor of the Arrhenious equation (In A). Both plots indicate compensation between the activation parameters. However, unlike the conventional plot, the Exner treatment is able to distinguish between two types of compensation. Furthermore, when extrapolated rate constants based on all the data in an Exner plot are transposed into E* vs. In A plots, so-called “turn-around” behavior is predicted for the effect of increasing phosphate concentration at constant pH. Such “turn-around” behavior in E* vs. In A plots has been observed experimentally by Beetlestone and co-workers for anion binding to human hemoglobin as a functin of pH. Lastly, the compensation temperatures obtained from these data all fall within the Vaslow-Doherty compensation range (250–350°K) which is thought to indicate that the solvent, water, is involved in the reaction mechanism. Thus, Exner plots appear to further resolve isokinetic temperatures of the Vaslow-Doherty type. Differences in the electrostriction of solvent in the activated state is suggested as one possible physical source for the Vaslow-Doherty type compensation observed in this work.     

Ascomycetous yeast species recovered from grapes damaged by honeydew and sour rot

Aims: To identify ascomycetous yeasts recovered from sound and damaged grapes by the presence of honeydew or sour rot. Methods and Results: In sound grapes, the mean yeast counts ranged from 3·20 ± 1·04 log CFU g^?1 to 5·87 ± 0·64 log CFU g^?1. In honeydew grapes, the mean counts ranged from 3·88 ± 0·80 log CFU g^?1 to 6·64 ± 0·77 log CFU g^?1. In sour rot grapes counts varied between 6·34 ± 1·03 and 7·68 ± 0·38 logCFU g^?1. Hanseniaspora uvarum was the most frequent species from sound samples. In both types of damage, the most frequent species were Candida vanderwaltii, H. uvarum and Zygoascus hellenicus. The latter species was recovered in high frequency because of the utilization of the selective medium DBDM (Dekkera/Brettanomyces differential medium). The scarce isolation frequency of the wine spoilage species Zygosaccharomyces bailii (in sour rotten grapes) and Zygosaccharomyces bisporus (in honeydew affected grapes) could only be demonstrated by the use of the selective medium ZDM (Zygosaccharomyces differential medium). Conclusions: The isolation of several species only from damaged grapes indicates that damage constituted the main factor determining yeast diversity. The utilization of selective media is required for eliciting the recovery of potentially wine spoilage species. Significance and Impact of the Study: The impact of damaged grapes in the yeast ecology of grapes has been underestimated.