Fluorescence characteristics of photoautotrophic soybean cells

We report here the first measurements on chlorophyll (Chl) a fluorescence characteristics of photoautotrophic soybean cells (cell lines SB-P and SBI-P). The cell fluorescence is free from severe distortion problems encountered in higher plant leaves. Chl a fluorescence spectra at 77 K show, after correction for the spectral sensitivity of the photomultiplier and the emission monochromator, peaks at 688, 696 and 745 nm, representing antenna systems of photosystem II-CP43 and CP47, and photosystem I, respectively. Calculations, based on the complementary area over the Chl a fluorescence induction curve, indicated a ratio of 6 of the mobile plastoquinone (including Q_B) to the primary stable electron acceptor, the bound plastoquinone Q_A. A ratio of one between the secondary stable electron acceptor, bound plastoquinone Q_B, and its reduced form Q_B ^- was obtained by using a double flash technique. Owing to this ratio, the flash number dependence of the Chl a fluorescence showed a distinct period of four, implying a close relationship to the S state of the oxygen evolution mechanism. Analysis of the Q_A ^- reoxidation kinetics showed (1) the halftime of each of the major decay components ( 300 s fast and 30 ms slow) increases with the increase of diuron and atrazine concentrations; and (2) the amplitudes of the fast and the slow components change in a complementary fashion, the fast component disappearing at high concentrations of the inhibitors. This implies that the inhibitors used are able to totally displace Q_B. In intact soybean cells, the relative amplitude of the 30 ms to 300 s component is higher (40:60) than that in spinach chloroplasts (30:70), implying a larger contribution of the centers with unbound Q_B. SB-P and SBI-P soybean cells display a slightly different sensitivity of Q_A ^- decay to inhibitors.Abbreviations CA complementary area over fluorescence induction curve - Chl chlorophyll, diuron - DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - F _m maximum chlorophyll a fluorescence - F ₀ minimum chlorophyll a fluorescence - F _v = F _t-F₀ - where F _v = variable chlorophyll a fluorescence - and F_t = chlorophyll a fluorescence at time t - PS II photosystem II - Q _a primary (plastoquinone) electron acceptor of PS II - Q _b secondary (plastoquinone) electron acceptor of PS II - t₅₀ the time at which the concentration of reduced Q _a is 50% of that at its maximum value     

Expression of recombinant antibody and secreted alkaline phosphatase in mammalian cells. Influence of cell line and culture system upon production kinetics

The growth and productivity of an Sp2/0 cell line, F3b10, expressing a recombinant antibody (rAb) and BHK21 cells expressing either the same rAb from the same plasmids (BHK.IgG) or secreted alkaline phosphatase (SEAP) (BHK.SEAP) were investigated. The F3b10 line was grown as a single cell suspension. The BHK lines were grown either as suspended natural aggregates or on Cytodex 3 microcarriers. The data for F3b10 showed that the cell-specific rAb production rate (Qs _rAb) increased in parallel with increases in the specific growth rate (). A similar result was obtained for suspended aggregate cultures of both recombinant BHK cell lines. In contrast, for microcarrier cultures of both BHK cell lines, Qs _product increased as decreased. This report shows that the relationship between cell growth and Qs _product for the cell lines and products studied is dependent upon the culture process. In systems where recombinant cells are growing as a single cell suspension or within a natural suspension aggregate, Qs _product increased with increases in . In such systems, the cells have a rounded morphology. When cells were grown on microcarriers, Qs _product decreased as increased. Cells growing attached to a surface are flat and elongated. The observed differences in the relationship of Qs _product to are correlated with changes in cell morphology. The relationship between Qs _product and is also affected by the choice of cell line. Correspondence to: A. J. Racher     

Proliferation of cultured glioma cells mediated by coenzyme Q<Subscript>10</Subscript> under conditions of serum deprivation

The effect of coenzyme Q₁₀ on glioma-cell proliferation under serum-deprived conditions has been studied. Our results have shown that the addition of coenzyme Q₁₀ into a serum-free culture medium enhances cell viability, stimulates cell growth, restores mitochondrial potential, and increases the quantity of energized mitochondria. It is found that coenzyme Q₁₀-induced glioma-cell proliferation in conditions of serum deficiency is a result of an intracellular reduced glutathione concentration with subsequent activation of protein kinase C, ERK1/2, and phosphoinositol-3-kinase.     

A hydrodynamical study of the flow in renal tubules

The hydrodynamical problem of flow in proximal renal tubule is investigated by considering axisymmetric flow of a viscous, incompressible fluid through a long narrow tube of varying cross-section with reabsorption at the wall. Two cases for reabsorption have been studied (i) when the bulk flow,Q, decays exponentially with the axial distancex, and (ii) whenQ is an arbitrary function ofx such thatQ-Q ₀ can be expressed as a Fourier integral (whereQ ₀ is the flux atx=0). The analytic expressions for flow variables have been obtained by applying perturbation method in terms of wall parameter ε. The effects of ε on pressure drop across the tube, radial velocity and wall shear have been studied in the case of exponentially decaying bulk flow and it has been found that the results are in agreement with the existing ones for the renal tubules.     

The effect of dynamic light regimes on Chlorella

The patterns of diurnal variations in pigmentation and optical cross-section were compared for two cyclostat cultures of Chlorella pyrenoidosa, where the dynamics of the photoperiod differed. Populations were light-limited, nutrient rich and growing on an 8:16 light-dark (LD) cycle. One light regime was an 8 h sine function of the light period (sinusoidal culture), while the second had an 1 h sine function super-imposed on the 8 hour sine function (oscillating sinusoidal culture). Hourly samples were taken throughout a 12 h period including the light period. Determinations were made of chlorophyll (Chl) a and b abundance, in vivo absorption spectra, cell number and volume and used to derive both cell-specific (cell) and optical chlorophyll specific (chl) cross sections, as well as the absorption efficiency, Q, of the cells. The results indicate that C. pyrenoidosa is capable of adapting to dynamics in light intensity within an 8 h photoperiod. The sinusoidal culture showed a constant decrease in the Chl a/b ratio of 28% while the total Chl content per cell increased slightly and chl and Q remained constant, suggesting coordinated changes in reaction centers and light harvesting complexes. Over the oscillating photoperiod, however, the second culture displayed a diurnal variation in Chl a/b ratio, a 20% increase in chl and an apparent oscillation in Q. These observations suggest that an oscillating photoperiod promoted the capability of Chl molecules to collect light and that the fractional area of all Chl molecules exposed to the photon flux is inversely related to the photon flux.     

Cellular Microcystin Content in N-Limited Microcystis aeruginosa Can Be Predicted from Growth Rate

Cell quotas of microcystin (Q_MCYST; femtomoles of MCYST per cell), protein, and chlorophyll a (Chl a), cell dry weight, and cell volume were measured over a range of growth rates in N-limited chemostat cultures of the toxic cyanobacterium Microcystis aeruginosa MASH 01-A19. There was a positive linear relationship between Q_MCYST and specific growth rate (μ), from which we propose a generalized model that enables Q_MCYST at any nutrient-limited growth rate to be predicted based on a single batch culture experiment. The model predicts Q_MCYST from μ, μ_max (maximum specific growth rate), Q_MCYSTmax (maximum cell quota), and Q_MCYSTmin (minimum cell quota). Under the conditions examined in this study, we predict a Q_MCYSTmax of 0.129 fmol cell⁻¹ at μ_max and a Q_MCYSTmin of 0.050 fmol cell⁻¹ at μ = 0. Net MCYST production rate (R_MCYST) asymptotes to zero at μ = 0 and reaches a maximum of 0.155 fmol cell⁻¹ day⁻¹ at μ_max. MCYST/dry weight ratio (milligrams per gram [dry weight]) increased linearly with μ, whereas the MCYST/protein ratio reached a maximum at intermediate μ. In contrast, the MCYST/Chl a ratio remained constant. Cell volume correlated negatively with μ, leading to an increase in intracellular MCYST concentration at high μ. Taken together, our results show that fast-growing cells of N-limited M. aeruginosa are smaller, are of lower mass, and have a higher intracellular MCYST quota and concentration than slow-growing cells. The data also highlight the importance of determining cell MCYST quotas, as potentially confusing interpretations can arise from determining MCYST content as a ratio to other cell components.     

N-acetylcysteine, coenzyme Q10 and superoxide dismutase mimetic prevent mitochondrial cell dysfunction and cell death induced by d-galactosamine in primary culture of human hepatocytes

d-Galactosamine (d-GalN) induces reactive oxygen species (ROS) generation and cell death in cultured hepatocytes. The aim of the study was to evaluate the cytoprotective properties of N-acetylcysteine (NAC), coenzyme Q₁₀ (Q₁₀) and the superoxide dismutase (SOD) mimetic against the mitochondrial dysfunction and cell death in d-GalN-treated hepatocytes. Hepatocytes were isolated from liver resections. NAC (0.5 mM), Q₁₀ (30 μM) or MnTBAP (Mn(III)tetrakis(4-benzoic acid) porphyrin chloride (1 mg/mL) were co-administered with d-GalN (40 mM) in hepatocytes. Cell death, oxidative stress, mitochondrial transmembrane potential (MTP), ATP, mitochondrial oxidized/reduced glutathione (GSH) and Q₁₀ ratios, electronic transport chain (ETC) activity, and nuclear- and mitochondria-encoded expression of complex I subunits were determined in hepatocytes. d-GalN induced a transient increase of mitochondrial hyperpolarization and oxidative stress, followed by an increase of oxidized/reduced GSH and Q₁₀ ratios, mitochondrial dysfunction and cell death in hepatocytes. The cytoprotective properties of NAC supplementation were related to a reduction of ROS generation and oxidized/reduced GSH and Q₁₀ ratios, and a recovery of mitochondrial complexes I + III and II + III activities and cellular ATP content. The co-administration of Q₁₀ or MnTBAP recovered oxidized/reduced GSH ratio, and reduced ROS generation, ETC dysfunction and cell death induced by d-GalN. The cytoprotective properties of studied antioxidants were related to an increase of the protein expression of nuclear- and mitochondrial-encoded subunits of complex I. In conclusion, the co-administration of NAC, Q₁₀ and MnTBAP enhanced the expression of complex I subunits, and reduced ROS production, oxidized/reduced GSH ratio, mitochondrial dysfunction and cell death induced by d-GalN in cultured hepatocytes.     

N‐Heterocyclic‐based adsorbents for antibody purification—effect of ligand structure

A new set of ligands based on substituted pyridine and other N‐heterocyclic structures, possessing an aliphatic primary amino group tether and an exocyclic sulphur atom, has been prepared and immobilized onto epoxy‐activated matrices such as Sepharose 6 Fast Flow®. The derived adsorbents have been evaluated for their utility to capture and purify humanized monoclonal antibodies. Favourable binding properties were assessed from screening assays to determine optimal conditions for the capture and elution of the monoclonal antibodies. Static and dynamic binding experiments were employed to derive the equilibrium dissociation constants K_D's and binding capacities Q_max's. Typically, the K_D values were in the range of 2–5 μM and the Q_max values between 20 and 75 mg mAb/ml resin, depending on the stereo‐electronic properties of the substituent in the N‐heterocyclic ring structure. The effect of ligand structure on the selectivity of these adsorbents was also investigated, and criteria for their use in the purification of monoclonal antibodies from cell culture supernatants established. Copyright © 2014 John Wiley & Sons, Ltd.     

Effect of oxygen on ubiquinone-10 production by Paracoccus denitrificans

Summary Ubiquinone-10 (Q₁₀) production was measured in batch cultures of Paracoccus denitrificans grown for 8 h at increasing oxygen concentrations (0–21 % O₂ in the sparging gas). Whereas the cellular level of Q₁₀ decreased monotonically from 1.2 to 0.5 mol/g d.w., the total yield of Q₁₀ was maximal at 2.5 % O₂ and amounted to 350 nmol (0.3 mg) per L of culture.     

Incorporating diffuse photosynthetically active radiation in a single-leaf model of canopy photosynthesis for a 56-year-old Douglas-fir forest

A simple top-down model of canopy photosynthesis (P) was developed and tested in this study. The model (referred to as the Q_e-MM model) is P = αQ _e P _max/(αQ _e + P _max), α and P _max are quantum-use efficiency and potential P, respectively. Q _e is given by Q _{d 0} + kQ _{b 0}, where Q _{d 0} and Q _{b 0} are the diffuse and direct photosynthetically active radiation (PAR) incident on the canopy, respectively. Q _e can be considered to be the effective incident PAR contributing to P and k is a measure of the contribution of Q _{b 0} to Q _e. When k = 1, the Q_e-MM model becomes the regular Michaelis-Menten type model of P (referred to as the MM model). A major objective of this study was to determine how well the Q_e-MM model could estimate P of a 56-year-old coastal Douglas-fir stand. To this end, we parameterized the Q_e-MM model using five and half years of eddy-covariance measurements of CO₂ flux above the Douglas-fir stand. The Q_e-MM model, with the incorporation of a function of air temperature, accounted for 74% of the variance in over 34,000 half-hourly P measurements. P estimated using the Q_e-MM model had no systematic errors with respect to Q _{d 0}. Although the Q_e-MM model has only one more parameter than the MM model, it accounted for 30% more variance in P than the latter when total incident PAR exceeded 900 μmol m⁻² s⁻¹. On average, k was found to be 0.22. We show that this small value of k reflects the significant effect of the scattering of the solar beam and the fraction of light-limited sunlit leaves. We also show that the success of the Q_e-MM model was due to the fact that a large fraction of the sunlit leaves were light-limited as a result of their orientation to the solar beam.     

Growth,fluorescence, photosynthetic O<Subscript>2</Subscript> production and pigment content of salt adapted cultures of <Emphasis Type="Italic">Arthrospira</Emphasis> (<Emphasis Type="Italic">Spirulina</Emphasis>) <Emphasis Type="Italic">platensis</Emphasis>

The effect of salt concentration (NaCl) on growth, fluorescence, photosynthetic activities and pigment content of the cyanobacterium Arthrospira platensis has been investigated over 15 days. It has been observed that high NaCl concentration induces an increase of the growth, photosynthetic efficiency (α), phycobilin/chlorophyll ratio and a slight decrease of dark respiration and compensation points. Moreover, high NaCl concentration enhances photosystem II (PSII) activity compared to photosystem I (PSI). Results show that the phycobilin-PSII energy transfer compared to the chlorophyll-PSII (F_695,600/F_695,440) increases. However, data obtained about the maximal efficiency of PSII photochemistry are controversial. Indeed, the Fv/Fm ratio decreases in salt adapted cultures, while at the same time the trapping flux per PSII reaction center (TR₀/RC) and the probability of electron transport beyond Q_A (₀) remain unchanged at the level of the donor and the acceptor sites of PSII. This effect can be attributed to the interference of phycobilin fluorescence with Chl a when performing polyphasic transient measurements.     

CHARACTERISTICS OF PHOSPHORUS LIMITATION IN CHLAMYDOMONAS REINHARDTH (CHLOROPHYCEAE) AND ITS PALMELLOIDS1

Chlamydomonas reinhardtii Dang, was grown in a chemostat culture under phosphate limitation. The steady state concentration of phosphate was below the detection limit (< 1 μg P/L) in all runs. The cellular content of phosphorus (Q_p), polyphosphate (Q_pp) and chlorophyll a increased with increasing dilution rate, and the growth rate of the alga was described by Q_p as well as Q_pp in the Droop model. The ratio Q_pp/Q_p and the activity of alkaline phosphatase were maximal at high and low growth rates, respectively. Palmelloids of Chlamydomonas were found at high dilution rates (D > 0.12 h^?1) and became attached to the wall of the culture vessel. They differed from the vegetative stage in both chemical composition and growth rate. Their contents of phosphorus and chlorophyll a were low, as in the vegetative cells, which grew at a low growth rate, whereas the ration Q_pp/Q_p and the activity of alkaline phosphatase were comparable with those of fast growing vegetative cells. The growth rate of the palmelloids was 0.03 h^?1 whereas maximum growth rate (μ_m) for the vegetative cells was 0.21 h^?1.     

Growth characteristics of Saccharomyces cerevisiae S288C in changing environmental conditions: auxo-accelerostat study

The effect of individual environmental conditions (pH, pO₂, temperature, salinity, concentration of ethanol, propanol, tryptone and yeast extract) on the specific growth rate as well as ethanol and glycerol production rate of Saccharomyces cerevisiae S288C was mapped during the fermentative growth in aerobic auxo-accelerostat cultures. The obtained steady-state values of the glycerol to ethanol formation ratio (0.1 mol mol⁻¹) corresponding to those predicted from the stoichiometric model of fermentative yeast growth showed that the complete repression of respiration was obtained in auxostat culture and that the model is suitable for calculation of Y _ATP and Q _ATP values for the aerobic fermentative growth. Smooth decrease in the culture pH and dissolved oxygen concentration (pO₂) down to the critical values of 2.3 and 0.8%, respectively, resulted in decrease in growth yield (Y _ATP) and specific growth rate, however the specific ATP production rate (Q _ATP) stayed almost constant. Increase in the concentration of biomass (>0.8 g dwt l⁻¹), propanol (>2 g l⁻¹) or NaCl (>15 g l⁻¹) lead at first to the decrease in the specific growth rate and Q _ATP, while Y _ATP was affected only at higher concentrations. The observed decrease in Q _ATP was caused by indirect rather than direct inhibition of glycolysis. The increase in tryptone concentration resulted in an increase in the specific growth rate from 0.44 to 0.62 h⁻¹ and Y _ATP from 12.5 to 18.5 mol ATP g dwt⁻¹. This study demonstrates that the auxo-accelerostat method, besides being an efficient tool for obtaining the culture characteristics, provides also decent conditions for the experiments elucidating the control mechanisms of cell growth.     

Photosystem II heterogeneity: the acceptor side

It is well known that two photosystems, I and II, are needed to transfer electrons from H₂O to NADP⁺ in oxygenic photosynthesis. Each photosystem consists of several components: (a) the light-harvesting antenna (L-HA) system, (b) the reaction center (RC) complex, and (c) the polypeptides and other co-factors involved in electron and proton transport. First, we present a mini review on the heterogeneity which has been identified with the electron acceptor side of Photosystem II (PS II) including (a) L-HA system: the PS II and PS II units, (b) RC complex containing electron acceptor Q₁ or Q₂; and (c) electron acceptor complex: Q_A (having two different redox potentials Q_L and Q_H) and Q_B (Q_B-type; Q'_B type; and non-Q_B type); additional components such as iron (Q-400), U (E_m,7=–450 mV) and Q-318 (or Aq) are also mentioned. Furthermore, we summarize the current ideas on the so-called inactive (those that transfer electrons to the plastoquinone pool rather slowly) and active reaction centers. Second, we discuss the bearing of the first section on the ratio of the PS II reaction center (RC-II) and the PS I reaction center (RC-I). Third, we review recent results that relate the inactive and active RC-II, obtained by the use of quinones DMQ and DCBQ, with the fluorescence transient at room temperature and in heated spinach and soybean thylakoids. These data show that inactive RC-II can be easily monitored by the OID phase of fluorescence transient and that heating converts active into inactive centers.Abbreviations DCBQ 2,5 or 2,6 dichloro-p-benzoquinone - DMQ dimethylquinone - Q_A primary plastoquinone electron acceptor of photosystem II - Q_B secondary plastoquinone electron acceptor of photosystem II - IODP successive fluorescence levels during time course of chlorophyll a fluorescence: O for origin, I for inflection, D for dip or plateau, and P for peak     

Levan production by Zymomonas mobilis cells. Attached to plaited spheres

In this work, an immobilization method for polymer-levan production by a non-flocculating Z mobilis culture was developed. The extent of cell attachment to the stainless steel wire surface, culture growth and product synthesis were described. It was established that during short-term passive immobilization of non-flocculation Z mobilis cells on a stainless steel wire surface, sufficient amounts of biomass for proper levan and ethano fermentation could not be obtained. Adherence of cells was improved by pressing the paste-like biomass within stainless steel spheres knitted from wire with subsequent dehydration. Biomass fixed in metal spheres was used for repeated batch fermentation of levan. The activation period of cells within wire spheres (WS) was 48 h in duration. During this time, cell growth stabilized at production levels of ethanol and levan of Q_eth = 1.238 g/l × h and q_eth = 0.47 g/l × h; Q_eth = 0.526 g/l × h and q_eth = 0.20 g/l × h. Five stable fermentation cycles were realized using one wire sphere inoculum, and maintaining a stable ratio of 2.4 of biomass suspended in the medium to biomass fixed in the sphere. Using fixed Z mobilis biomass in the WS, the total amount of inoculum could be reduced for batch fermentation. Large plaited wire spheres with biomass may have potential in fermentation in viscous systems, including levan production.     

Kinetics of yeast growth and enzyme syntheses in a phosphate-limited continuous culture

Summary The effect of a deficiency of inorganic phosphate on the growth rate and on the invertase and phosphatase activities inSaccharomyces carlsbergensis was studied in a chemostat culture using a synthetic medium in which ethanol was the sole carbon source.The kinetic relationship between the growth rate and both the rates of phosphate uptake and the ethanol consumption agreed well with the threshold model but not the multicative model. The invertase activity of the yeast increased as the dilution rate decreased. As the phosphate concentration in the feed was reduced, the enzyme synthesis increased remarkably. Acid phosphatase activity was repressed completely above a critical molecular ratio, 0.015, of monopotassium phosphate to ethanol in the feed medium. As the phosphate concentration in the feed decreased, the maximum specific enzyme activity increased and the corresponding optimum dilution rate decreased. These experimental changes in enzyme synthesis were expressed mathematically using the modified operon models for enzyme regulation in terms of two fractions of limited inorganic phosphate; one which affects growth and the other which is incorporated in excess by the cells.Nomenclature A ethanol concentration in the culture (mM) - a, b, c, d exponents in the operon model - D dilution rate (h^–1) - E enzyme concentration in the culture (enzyme unit l^–1) - K_a, K_b, K_c, K_d, k equilibrium constants used in the operon model, see Toda (1976b) - o operator gene - P inorganic phosphate concentration in the culture (mM) - Pi limited inorganic phosphate concentration in the cells (mmole inorganic phosphate/g dry weight of cell) - Q specific enzyme activity, no units: (E/X)/(E/X)_max - Q_c, Q_d as defined in Eq. 12 - R repressor - r regulator gene - X cell concentration in the culture (dry cell weight l^–1) Greek Letters molecular ratio of inorganic phosphate to ethanol in the feed medium (mole/mole) - specific growth rate (h^–1) - A specific uptake rate of ethanol (mmole/g cell·h) - P specific uptake rate of inorganic phosphate (mmole/g cell·h) Suffix crit critical value - f feed - max maximum - min minimum - t total - 1, 2 number of species Superfix eff effective for cell growth - exc excess - str structural     

Sulfide-quinone and sulfide-cytochrome reduction in Rhodobacter capsulatus

The reduction by sulfide of exogenous ubiquinone is compared to the reduction of cytochromes in chromatophores of Rhodobacter capsulatus. From titrations with sulfide values for V_max of 300 and 10 moles reduced/mg bacteriochlorophyll a·h, and for K_m of 5 and 3 M were estimated, for decyl-ubiquinone-and cytochrome c-reduction, respectively. Both reactions are sensitive to KCN, as has been found for sulfide-quinone reductase (SQR) in Oscillatoria limnetica, which is a flavoprotein. Effects of inhibitors interfering with quinone binding sites suggest that at least part of the electron transport from sulfide in R. capsulatus employs the cytochrome bc ₁-complex via the ubiquinone pool.Abbreviations BChl a bacteriochlorophyll a - DAD diaminodurene - decyl-UQ decyl-ubiquinone - LED light emitting diode - NQNO 2-n-nonyl-4-hydroxyquinoline-N-oxide - PQ-1 plastoquinone 1 - SQR sulfide-quinone reductase (E.C. 1.8.5.'.) - UQ ubiquinone 10 - Q_c the quinone reduction site on the cytochrome b ₆ f/bc ₁, complex (also termed Q_i or Q_r or Q_n) - Q_s the quinone reduction site on SQR - Q_z quinol oxidation site on the b ₆ f/bc ₁, complex (also termed Q_o or Q_p)     

Batch xylitol production by<Emphasis Type="Italic"> Candida guilliermondii</Emphasis> FTI 20037 from sugarcane bagasse hemicellulosic hydrolyzate at controlled pH values

Batch fermentation of sugarcane bagasse hemicellulosic hydrolyzate by the yeast Candida guilliermondii FTI 20037 was performed using controlled pH values (3.5, 5.5, 7.5). The maximum values of xylitol volumetric productivity (Q _p=0.76 g/l h) and xylose volumetric consumption (Q _s=1.19 g/l h) were attained at pH 5.5. At pH 3.5 and 7.5 the Q _p value decreased by 66 and 72%, respectively. Independently of the pH value, Y _x/s decreased with the increase in Y _p/s suggesting that the xylitol bioconversion improves when the cellular growth is limited. At the highest pH value (7.5), the maximum specific xylitol production value was the lowest (q _pmax=0.085 g/l h.), indicating that the xylose metabolism of the yeast was diverted from xylitol formation to cell growth.List of symbols P _max xylitol concentration (g/l) - Q _x volumetric cell production rate (g/l h) - Q _s volumetric xylose uptake rate (g/l h) - Q _p volumetric xylitol production rate (g/l h) - q _pmax specific xylitol production (g/g h) - q _smax specific xylose uptake rate (g/g h) - _max specific cell growth rate (h^–1) - Y _p/s xylitol yield coefficient, g xylitol per g xylose consumed (g/g) - Y _p/x xylitol yield coefficient, g xylitol per g dry cell mass produced (g/g) - Y _x/s cell yield coefficient, g dry cell mass per g xylose consumed (g/g) - _cell percentage of the cell yield from the theoretical value (%) - _xylitol percentage of xylitol yield from the theoretical value (%)     

Stereochemistry and Stereoelectronics of Azines. 13. Conformational Effects on the Quadrupolarity of Azines. An Ab Initio Quantum-Mechanical Study of a Lateral Synthon

The quadrupole moment of formaldazine, H₂C=N-N=CH₂, has been studied for the trans structure (Ð(C-N-N-C) = = 180) and a series of gauche structures ( > 120). Restricted Hartree-Fock theory, second-order Møller-Plesset theory, and quadratic CI theory have been used in conjunction with the basis sets 6-31G^*, 6-31G**, 6-311G** and 6-311++G**. Formaldazine is a quadrupolar molecule with primitive quadrupole moment tensor components of Q _xx = -22.4, Q _yy = -20.4 and Q _zz = -25.6 DÅ at the theoretical level QCISD/6-311++G**. The examination of the theoretical level dependency shows that the reliable computation of a quadrupole moment requires the use of a flexible basis set. A large part of the component Q _zz = -25.6 DÅ is due to the -system and compares, on a per electron basis, with the Q _zz value of benzene. Conformational changes of the azines in the range 120° < < 180 have but a minute effect on the energy and are associated with only minor electronic relaxation. These conformational changes alter the quadrupole moment tensor components less than Q _xx = +0.4, Q _yy = +1.6 and Q _zz = -1.0 DÅ at QCISD/6-311++G**//QCISD/6-31G*. The direction of these changes is explained by consideration of the rotation of the CN--systems and a small reduction of the CN bond polarity in the gauche structures. The Q _zz component of formaldazine is representative of the quadrupole moment tensor component along the direction of the C ₂ axis of the azine bridge as such. Hence, the results of this study suggest that azines can engage in strong quadrupole-quadrupole interactions and can be employed as lateral synthons in crystal engineering. Electronic Supplementary Material available.     

Carbon quality and soil microbial property control the latitudinal pattern in temperature sensitivity of soil microbial respiration across Chinese forest ecosystems

Understanding the temperature sensitivity (Q₁₀) of soil organic C (SOC) decomposition is critical to quantifying the climate–carbon cycle feedback and predicting the response of ecosystems to climate change. However, the driving factors of the spatial variation in Q₁₀ at a continental scale are fully unidentified. In this study, we conducted a novel incubation experiment with periodically varying temperature based on the mean annual temperature of the soil origin sites. A total of 140 soil samples were collected from 22 sites along a 3,800 km long north–south transect of forests in China, and the Q₁₀ of soil microbial respiration and corresponding environmental variables were measured. Results showed that changes in the Q₁₀ values were nonlinear with latitude, particularly showing low Q₁₀ values in subtropical forests and high Q₁₀ values in temperate forests. The soil C:N ratio was positively related to the Q₁₀ values, and coniferous forest soils with low SOC quality had higher Q₁₀ values than broadleaved forest soils with high SOC quality, which supported the “C quality temperature” hypothesis. Out of the spatial variations in Q₁₀ across all ecosystems, gram‐negative bacteria exhibited the most importance in regulating the variation in Q₁₀ and contributed 25.1%, followed by the C:N ratio (C quality), fungi, and the fungi:bacteria ratio. However, the dominant factors that regulate the regional variations in Q₁₀ differed among the tropical, subtropical, and temperate forest ecosystems. Overall, our findings highlight the importance of C quality and microbial controls over Q₁₀ value in China's forest ecosystems. Meanwhile, C dynamics in temperate forests under a global warming scenario can be robustly predicted through the incorporation of substrate quality and microbial property into models.