The Use of the [13C]/[12C] Ratio for the Assay of the Microbial Oxidation of Hydrocarbons

The study deals with a comparative analysis of the relative abundances of the carbon isotopes ¹²C and ¹³C in the metabolites and biomass of the Burkholderia sp. BS3702 and Pseudomonas putida BS202-p strains capable of utilizing aliphatic (n-hexadecane) and aromatic (naphthalene) hydrocarbons as sources of carbon and energy. The isotope compositions of the carbon dioxide, biomass, and exometabolites produced during the growth of Burkholderia sp. BS3702 on n-hexadecane (¹³C = –44.6 ± 0.2) were characterized by the values of ¹³C_{CO 2} = –50.2 ± 0.4, ¹³C_biom = –46.6 ± 0.4, and ¹³C_exo = –41.5 ± 0.4, respectively. The isotope compositions of the carbon dioxide, biomass, and exometabolites produced during the growth of the same bacterial strain on naphthalene (¹³C = –21 ± 0.4) were characterized by the isotope effects ¹³C_{CO 2} = –24.1 ± 0.4, ¹³C_biom = –19.2 ± 0.4, and ¹³C_exo = –19.1 ± 0.4, respectively. The possibility of using the isotope composition of metabolic carbon dioxide for the rapid monitoring of the microbial degradation of petroleum hydrocarbons in the environment is discussed.     

Pyridoxal-5′-phosphate derivatives of substance P: Preparation,spasmogenic activity,and degradation by human plasma

Two fluorescent derivatives of substance P (SP) (Arg-Pro-Lys-Pro-Gln-Gln-Phe-Phe-Gly-Leu-Met-NH₂) were prepared by chemical modification of the native peptide by pyridoxal-5-phosphate (pyridoxal-P). The formation of both pyridoxal-P-derivatives of SP is the result of one modification procedure. The determination of the amino acid composition showed that in one of the derivatives the -amino group of the Lys residue [-(P-pxy)-SP] and in the other the -amino group of the Lys residue and also the N-terminal amino group [,-di-(P-pxy)-SP] of SP had been substituted by pyridoxal-P. -(P-pxy)-SP and ,-di-(P-pxy)-SP have spasmogenic activity with ED₅₀ of 1.8×10^–9 and 4×10^–9 M, respectively, tested on isolated guinea pig ileum. The fluorescence of P-pxy residues permits detection of as little as 1 pmol/ml of -(P-pxy)-SP and 0.5 pmol/ml of ,-di-(P-pxy)-SP. Both analogues of SP obtained are degraded by human plasma more slowly than the native peptide.Abbreviations SP substance P - pyridoxal-P pyridoxal-5-phosphate - P-pxy phospho-pyridoxyl residue - -(P-pxy)-SP substance P modified by pyridoxal-P at the -amino group of the Lys residue - ,-di-(P-pxy)-SP substance P modified by pyridoxal-P at the -amino group of the Lys residue and the N-terminal amino group of SP - (P-pxy)-Lys Lys modified by pyridoxal-P at the -amino group     

The quantitative analysis of chromosome pairing and chiasma formation based on the relative frequencies of M I configurations

Whilst reliable estimates of chiasma frequencies can usually not be obtained, the probability (b) of a chromosome arm to be bound by at least one chiasma can often be determined. In the absence of interference this probability equals (1–e ^–2), where 2 is the average chiasma frequency of the chromosome arm and the average crossover frequency or map length. In the presence of interference is shown to retain its genetic meaning as an additive metric that may describe the chromosome arm or other distinctive chromosome segment in terms of genetic recombination. It is a form of potential map length, comparable to, but numerically different from the regular map length. It is termed provisionally crossing-over potential.A chromosome with armsm andn with crossing-over potentials and will form ring bivalents with a frequency (1–e ^–2).(1–e ^–2); open bivalents with a frequency (1–e ^–2).e ^–2+(1–e ^–2).e ^–2; univalent pairs with a frequencye ^–2.e ^–2. Estimates of these frequencies yield equations from which and may be solved. In rye (Secale cereale) their ratio (q) is approximately two and differs from the mitotic arm length ratio of 1.4, indicating localization of chiasmata in the long arms.Graphs are given to show how, with constantq, the relation between the probabilitiesb _m andb _n of the two arms being bound changes with changing averageb.Data are presented on chiasma frequencies in M I, and compared with the frequencies expected in the absence of interference to give an impression of the degree of interference. Apparent fusion of chiasmata simulates interference.     

Structures of asparagine linked oligosaccharides of immunoglobulins (IgY) isolated from egg-yolk of Japanese quail

Structures of the Asn linked oligosaccharides of quail egg-yolk immunoglobulin (IgY) were determined in this study. Asn linked oligosaccharides were cleaved from IgY by hydrazinolysis and labelled withp-aminobenzoic acid ethyl ester (ABEE) afterN-acetylation. The ABEE labelled oligosaccharides were then fractionated by a combination of Concanavalin A-agarose column chromatography and anion exchange, normal phase and reversed phase HPLC before their structures were determined by sequential exoglycosidase digestion, methylation analysis, HPLC, and 500 MHz¹H-NMR spectroscopy. Quail IgY contained only neutral oligosaccharides of the following categories: the glucosylated oligomannose type (0.6%, Glc1-3Glc1-3Man₉GlcNAc₂; 35.6%, Glc1-3Man_7–9GlcNAc₂). oligomannose type (15.0%, with the structure Man_5–9GlcNAc₂) and biantennary complex type with core structures of-Man1-3(-Man1-6)Man1-4GlcNAc1-4GlcNAc (9.9%),-Man1-3(GlcNAc1-4)(-Man1-6)Man1-4GlcNAc1-4GlcNAc (25.1%) and-Man1-3(GlcNAc1-4)(-Man1-6)Man1-4GlcNAc1-4(Fuc1-6)GlcNAc (11.4%). Although never found in mammalian proteins, glucosylated oligosaccharides (Glc₁Man_7–9GlcNAc₂) have been located previously in hen IgY.Abbreviations IgG, IgM, IgA, IgY immunoglobulin G, M, A and Y, respectively - ABEE p-aminobenzoic acid ethyl ester     

Electrical characteristics of sensory neurons of Hirudo medicinalis

During intracellular polarization of identified sensory neurons of the leech by square pulses of hyperpolarizing current electrical parameters of the cell membranes were determined: input resistance of the neuron R_n, time constant of the membrane , the ratio between conductance of the cell processes and conductance of the soma , the resistance of the soma membrane r_s, the input resistance of the axon r _a , capacitance of the membrane C_s, and resistivity of the soma membrane R_s. The results obtained by the study of various types of neurons were subjected to statistical analysis and compared with each other. Significant differences for neurons of N- and T-types were found only between the values of , C_s, and R_s (P<0.01). These parameters also had the lowest coefficients of variation. The surface area of the soma of the neurons, calculated from the capacitance of the membrane (the specific capacitance of the membrane was taken as 1 µF/cm²) was 7–10 times (N-neurons) or 4–6 times (T-neurons) greater than the surface area of a sphere of the same diameter. The resistivity of the soma membrane R_s was 35.00 k·cm² for cells of the N-type and 19.50 k·cm² for T-neurons. The reasons for the relative stability of this parameter compared with the input resistance of the cell (coefficient of variation 22–7 and 53–31% respectively) are discussed. The possible effects of electrical characteristics on the properties of repeated discharges in neurons of different types also are discussed.A. A. Zhdanov Leningrad State University. Translated from Neirofiziologiya, Vol.7, No.3, pp.295–301, May–June, 1975.     

Cell recycling studies for α-amylase production by Bacillus amyloliquefaciens

Production of -amylase by a strain of Bacillus amyloliquefaciens was investigated in a cell recycle bioreactor incorporating a membrane filtration module for cell separation. Experimental fermentation studies with the B. amyloliquefaciens strain WA-4 clearly showed that incorporating cell recycling increased -amylase yield and volumetric productivity as compared to conventional continuous fermentation. The effect of operating conditions on -amylase production was difficult to demonstrate experimentally due to the problems of keeping the permeate and bleed rates constant over an extended period of time. Computer simulations were therefore undertaken to support the experimental data, as well as to elucidate the dynamics of -amylase production in the cell recycle bioreactor as compared to conventional chemostat and batch fermentations. Taken together, the simulations and experiments clearly showed that low bleed rate (high recycling ratio) various a high level of -amylase activity. The simulated fermentations revealed that this was especially pronounced at high recycling ratios. Volumetric productivity was maximum at a dilution rate of around 0.4 h^–1 and a high recycling ratio. The latter had to exceed 0.75 before volumetric productivity was significantly greater than with conventional chemostat fermentation.List of Symbols a proportionality constant relating the specific growth rate to the logarithm of G (h) - a ₁ reaction order with respect to starch concentration - a ₂ reaction order with respect to glucose concentration - B bleed rate (h^–1) - C starch concentration (g/l) - C ₀ starch concentration in the feed (g/l) - D dilution rate (h^–1) - D _E volumetric productivity (KNU/(mlh)) - e intracellular -amylase concentration (g/g cell mass) - E extracellular -amylase concentration (KNU/ml) - F volumetric flow rate (l/h) - G average number of genome equivalents of DNA per cell - k _l intracellular equilibrium constant - k ₂ intracellular equilibrium constant - k _s Monod saturation constant (g/l) - k ₃ excretion rate constant (h^–1) - k _d first order decay constant (h^–1) - k _gl rate constant for glucose production - k _st rate constant for starch hydrolysis - k _t1 proportionality constant for -amylase production (gmRNA/g substrate) - k ₁ translation constant (g/(g mRNAh)) - KNU kilo Novo unit - m maintenance coefficient (g substrate/(g cell massh)) - n number of binding sites for the co-repressor on the cytoplasmic repressor - Q repression function K₁/K₂Q1.0 - R ratio of recycling - R _s rate of glucose production (g/lh) - r _c rate of starch hydrolysis (g/(lh)) - R _eX retention by the filter of the compounds X: starch or -amylase - r intracellular -amylase mRNA concentration (g/g cell mass) - r _C volumetric productivity of starch (g/lh) - r _E volumetric productivity of intracellular -amylase (KNU/(g cell massh)) - r _r volumetric productivity of intracellular mRNA (g/(g cell massh)) - r _e volumetric productivity of extracellular -amylase (KNU/(mlh)) - r _s volumetric productivity of glucose (g/(lh)) - r _X volumetric productivity of cell mass (g/(lh)) - S ₀ free reducing sugar concentration in the feed (g/l) - S extracellular concentration of reducing sugar (g/1) - t time (h) - V volume (l) - X cell mass concentration (g/l) - Y yield coefficient (g cell mass/g substrate) - Y _E/S yield coefficient (KNU -amylase/g substrate) - Y _E total amount of -amylase produced (KNU) - substrate uptake (g substrate/(g cell massh)) - specific growth rate of cell mass (h^–1) - _d specific death rate of cells (h^–1) - _m maximum specific growth rate of cell mass (h^–1) This study was supported by Bioprocess Engineering Programme of the Nordic Industrial Foundation and the Center for Process Biotechnology, the Technical University of Denmark.     

Theoretical stability diagram of solvent-containing black lipid films

Recently, we have developed an analytical, semi-microscopic theory for the macroscopic behavior of a solvent-containing black lipid film subjected to an electric cross film voltage, . Here we employ the theoretical expressions derived for the disjoining pressure, _D, the film elasticity, _F, and the film tension, _F, to construct the stability diagram of the film, in the _D-. Depending on its state (_D, ), the film is stable or is prone to squeezing or bending deformations. For a monooleate film we show how the destruction of the plane film due to a periodic thickness fluctuation (squeezing) is facilitated by two mechanisms: i) lowering of _D at fixed ; ii) lowering of at fixed _D, provided that the film is in a stable state characterized by _D<–7.03×10³ dyne/cm² and >0 mV. Bending of a low tension film (single interface tension _s 0.025 dyne/cm¹) can be achieved only for >170 mV and _D > –8.7 × 10⁴ dyne/cm². Finally, we demonstrate the existence of a marginal state ( _D ⁰ , ⁰) where the film is predicted to exhibit strong fluctuations both in the squeezing and in the bending mode.     

Hydrodynamic characteristics of two-phase inverse fluidized bed

Hydrodynamic characteristics of a new mode of liquid-solid fluidization, termed as inverse fluidization in which low density floating particles are fluidized with downward flow of liquid, are experimentally investigated. The experiments are carried out with low density particles (<534 kg/m³) which allow high liquid throughputs in the system. During the operation, three regimes, namely, packed, semi-fluidization and fully fluidization are encountered. Empirical correlations are proposed to predict the pressure drop in each regime. A computational procedure is developed to simulate the variation of pressure drop with liquid velocity.List of Symbols Ar modified Archimedes number, d _p ³ (– _s)g/² - d _p particle diameter, mm - f friction factor (eq. 2) - g acceleration due to gravity, m/s² - H total bed height, m - H _c height of the column, m - H_f height of fluidized bed, m - H₀ height of initial bed, m - H_p height of the packed bed, m - (p) pressure drop across the bed, N/m² - (p) _f pressure drop across fluidized bed section, N/m² - (p) _p pressure drop across the packed bed section, N/m² - (p) _sf total pressure drop in semifluidization regime, N/m² - Re Reynolds number, d _pU ₁/ - Re_m modified Reynolds number, d _pU ₁/(1– _p) - U ₁ superficial liquid velocity, m/s - U_mf minimum fluidization velocity, m/s - U_osf onset fluidization velocity, m/s Greek Letters _f voidage of fluidized bed - _p voidage of packed bed - liquid viscosity, kg/ms - liquid density, kg/m³ - _s particle density, kg/m³     

Mode of uptake of sterol by Arthrobacter simplex

The mechanism of uptake of water-insoluble -sitosterol by a newly isolated strain of Arthrobacter simplex SS-7 was studied. The production of an extracellular sterol-pseudosolubilizing protein during growth of A. simplex on -sitosterol was demonstrated by isolating the factor from the cell-free supernatant and its subsequent purification by Sephadex G-150 column chromatography. The M _r of the purified sterol-pseudosolubilizing protein determined by SDS–PAGE was 19kDa. The rate of sterol pseudosolubilization (5.2×10^–3g l^–1h^–1) could not adequately account for the rate of sterol uptake (72×10^–3g l^–1h^–1) and the specific growth rate (56×10^–3 h^–1). However in the unfavourable growth condition, when the cells were treated with sodium azide at the level of 30–60% of MIC, the sterol pseudosolubilization accounted for nearly 74% of the total growth containing 96% free cells. Cellular adherence to substrate particles was found to play an active role in the normal growth of the strain on -sitosterol. Unlike sodium acetate-grown cells, whose surface activity was negligible (60mNm^–1), the sterol-grown cells had strong surface activity (40mNm^–1). The high lipid content and long chain fatty acids in the cell-wall of -sitosterol-grown cells probably contribute to the high sterol adherence activity of the cells.     

Enzymic synthesis of the trisaccharide core region of the carbohydrate chain ofN-glycoprotein

Transmannosylation from mannotriose (Man1-4Man1-4Man) to the 4-position at the nonreducing end N-acetylglucosaminyl residue ofN,N-diacetylchitobiose was regioselectively induced through the use of -d-mannanase fromAspergillus niger. The enzyme formed the trisaccharide Man1-4GlcNAc1-4GlcNAc (3.7% of the enzyme-catalysed net decrease ofN,N-diacetylchitobiose) from mannotriose as a donor andN,N-diacetylchitobiose as an acceptor. Mannobiose (Man1-4Man) was also shown to be useful as a donor substrate for the desired trisaccharide synthesis.Abbreviations Man d-mannose - (M _n) (n=1–5) -linkedn-mer of mannose - GlcNAc₂ 2-acetamido-2-deoxy--d-glucopyranosyl-(1–4)-2-acetamido-2-deoxy-d-glucose     

Age and Growth of the Whiskery Shark, Furgaleus macki, from Southwestern Australia

Age and growth of the whiskery shark, Furgaleus macki, from southwestern Australia were examined using vertebral ageing and tag-recapture data. The readability of bands on the vertebral centra varied markedly between individuals. Four readers were used to make band counts, with the most experienced reader having the lowest index of average percent error and the highest level of agreement with final counts. Marginal increment analysis indicated that opaque bands form in January. With parturition occurring from August to October, size data suggests that the first band is probably formed 15–17 months after birth. The age at maturity was estimated to be 4.5 years for males, and 6.5 years for females. The oldest male was 10.5 years, and oldest female was 11.5 years. Von Bertalanffy growth parameters for males were L =121.5cm fork length, K=0.423 year^–1, t ₀=–0.472 years, were L =120.7cm fork length, K=0.369 year^–1, t ₀=–0.544 years for females, and were L =118.1cm fork length, K=0.420 year^–1, t ₀=–0.491 years for combined sexes. Data from a tag recapture study were analysed using a maximum likelihood method to verify the estimates of growth parameters from vertebral ageing. Von Bertalanffy growth parameters from the tag recapture study were L =128.2cm fork length, K=0.288 year^–1, t ₀=–0.654 years. The two methods of estimating growth parameters produced similar results, with rapid growth until approximately 5 years of age, after which there was little increase in length.     

Effects of <Emphasis Type="Italic">in vitro</Emphasis>rooting environments and irradiance on growth and photosynthesis of strawberry plantlets during acclimatization

Strawberry (Fragaria ananassaDuch. cv. Fengxiang) plantlets were cultured under two in vitroenvironments for rooting, and then acclimatized under two ex vitroirradiance conditions. At the end of rooting stage plant height, fresh weight and specific leaf area of T1-plants grown under high sucrose concentration (3 sucrose), low photosynthetic photon flux density (30 mol m^–2 s^–1) and normal CO₂ concentration (350–400 l l^–1) were significantly higher than those of T2-plantlets grown under low sucrose concentration (0.5), high photosynthetic photon flux density (90 mol m^–2 s^–1) and elevated CO₂ concentration (700–800 l l^–1). But T2-plantlets had higher net photosynthetic rate (Pn), effective photochemical quantum yield of PSII (_PSII), effective photosynthetic electron transport rate (ETR), photochemical quenching (q_P) and ratio of chlorophyll fluorescence yield decrease (Rfd). After transfer, higher irradiance obviously promoted the growth of plantlets and was beneficial for the development of photosynthetic functions during acclimatization. T2-plantlets had higher fresh weight, leaf area, _PSII and ETR under higher ex vitroirradiance condition.     

A new α2HS-glycoprotein typing by isoelectric focusing

Summary Isoelectric focusing (pH 4.0–5.0) of serum ₂HS-glycoprotein on polyacrylamide gels has been found to be a useful tool in population genetics and forensic science. Using this method, we isolated three common types, ₂HS 1-1, ₂HS 2-1 and ₂HS 2-2, and showed that ₂HS types are determined by two autosomal codominant alleles, ₂ HS ¹ and ₂ HS ². The method is simple, fast and easy to perform. Results of typing for the two alleles, ₂ HS ¹ and ₂ HS ², are described for a Japanese population sample (n=1003).     

Average phase difference theory and 1∶1 phase entrainment in interlimb coordination

The dynamics of coupled biological oscillators can be modeled by averaging the effects of coupling over each oscillatory cycle so that the coupling depends on the phase difference between the two oscillators and not on their specific states. Average phase difference theory claims that mode locking phenomena can be predicted by the average effects of the coupling influences. As a starting point for both empirical and theoretical investigations, Rand et al. (1988) have proposed d/dt= — K sin ), with phase-locked solutions =arcsin( /K), where is the difference between the uncoupled frequencies and K is the coupling strength. Phase-locking was evaluated in three experiments using an interlimb coordination paradigm in which a person oscillates hand-held pendulums. was controlled through length differences in the left and right pendulums. The coupled frequency _c was varied by a metronome, and scaled to the eigenfrequency _v of the coupled system K was assumed to vary inversely with _c. The results indicate that: (1) and K contribute multiplicatively to (2) =0 or = regardless of K when =0; (3) 0 or regardless of when K is large (relative to ); (4) results (1) to (3) hold identically for both in phase and antiphase coordination. The results also indicate that the relevant frequency is _c/_v rather than _c. Discussion high-lighted the significance of confirming =arcsin(/K) for more general treatments of phase-locking, such as circle map dynamics, and for the 11 phase-entrainment which characterizes biological movement systems.     

Effect of Neurotensin Peptidomimetics on Thermoregulation in Rats

The effects of the tripeptide analogues of neurotensin, GZR123 and GZR125, on thermoregulation was studied in rats that were kept at different ambient temperatures ( _c): in the cold ( _c = 4–6°C), thermoneutral ( _c = 27–28°C), and hot ( _c = 31–32°C) environment, as well as at room temperature ( _c = 20–21°C). In the cold environment, the injection of GZR123 disturbed the vegetative mechanisms of heat emission, leading to peripheral vasoconstriction and possibly changing heat production. Similar to neurotensin, GZR125 disturbed the development of compensatory vasoconstriction in the cold environment and at room temperature, which resulted in a decrease in body temperature. At high temperature, this peptide induced vasodilation.     

Inheritance of the dwarf plant type in blackgram (Vigna mungo (L.) Hepper)

Summary The inheritance of the dwarf plant type was studied in blackgram (V. mungo (L.) Hepper). Type 9 has erect plant type with normal internode length. The mutant line, EMSD has reduced internode length. The F₁, F₂ and F₃ generations of a cross between Type 9 and EMSD and its reciprocal were studied. The extreme dwarf plant type appeared to be governed by a single recessive gene, dw ₁ dw ₁ with no cytoplasmic effect.Part of Ph.D. Thesis submitted by the first author     

Studies on adenosine triphosphate transphosphorylases. XVIII. Synthesis and preparation of peptides and peptide fragments of rabbit muscle ATP-AMP transphosphorylase (adenylate kinase) and their nucleotide-binding properties

Two peptide fragments, derived from the head and tail of rabbit muscle myokinase, were found to possess remarkable and specific ligand-binding properties (Hamadaet al., 1979).By initiating systematic syntheses and measurements of equilibrium substrate-binding properties of these two sets of peptides, or portions thereof, which encompass the binding sites for (a) the magnesium complexes of the nucleotide substrates (MgATP^2– and MgADP^–) and (b) the uncomplexed nucleotide substrates (ADP^3– and AMP^2–) of rabbit muscle myokinase, some of the requirements for binding of the substrates to ATP-AMP transphosphorylase are being deduced and chemically outlined. One requirement for tight nucleotide binding appears to be a minimum peptide length of 15–25 residues. In addition, Lys-172 and/or Lys-194 may be involved in the binding of AMP.The syntheses are described as a set of peptides corresponding to residues 31–45, 20–45, 5–45, and 1–45, and a set of peptides corresponding to residues 178–192, 178–194, and 172–194 of rabbit muscle adenylate kinase. The ligand-binding properties of the first set of synthetic peptides to the fluorescent ligands: MgATP/ATP and MgADP/ADP are quantitatively presented in terms of their intrinsic dissociation constants (K_d) and values ofN (maximal number of moles bound per mole of peptide); and compared with the peptide fragment MT-I (1–44) obtained from rabbit muscle myokinase (Kubyet al., 1984) and with the native enzyme (Hamadaet al., 1979). In addition, the values ofN andK_d are given for the second set of synthetic peptides to the fluorescent ligands AMP and ADP as well as for the peptide fragments MT-XII(172–194) and CB-VI(126–194) (Kuby et al., 1984) and, in turn, compared with the native enzyme.A few miscellaneous dissociation constants which had been derived kinetically are also given for comparison (e.g., theK _i for AMP and the value of obtained for the native enzyme) (Hamada and Kuby, 1978), and theK'_d measured for Cr³⁺ and the synthetic peptide I_1–45 (Fryet al., 1985b).Paper XVII of this series is Kubyet al. (1983).     

Electrochemical potential of protons in vesicles reconstituted from purified,proton-translocating adenosine triphosphatase

Summary Measurements were made of the difference in the electrochemical potential of protons ( ) across the membrane of vesicles reconstituted from the ATPase complex (TF ₀ ·F ₁) purified from a thermophilic bacterium and P-lipids. Two fluorescent dyes, anilinonaphthalene sulfonate (ANS) and 9-aminoacridine (9AA) were used as probes for measuring the membrane potential () and pH difference across the membrane ( pH), respectively.In the presence of Tris buffer the maximal and no pH were produced, while in the presence of the permeant anion NO ₃ ^– the maximal pH and a low were produced by the addition of ATP. When the ATP concentration was 0.24mm, the was 140–150 mV (positive inside) in Tris buffer, and the pH was 2.9–3.5 units (acidic inside) in the presence of NO ₃ ^– . Addition of a saturating amount of ATP produced somewhat larger and pH values, and the attained was about 310 mV.By trapping pH indicators in the vesicles during their reconstitution it was found that the pH inside the vesicles was pH 4–5 during ATP hydrolysis.The effects of energy transfer inhibitors, uncouplers, ionophores, and permeant anions on these vesicles were studied.     

Structure and variation of the Paraguay River phytoplankton in two periods of its hydrological cycle

The structure and distribution of the Paraguay River phytoplankton (between 16° 03 and 26° 53 S and between 57° 13 and 58° 23 W was studied during June–July/95 and December/95–January/96. Phytoplankton density values were lower in winter (mean value between 731 and 878 ind. ml^–1) in summer (between 1113 and 1876 ind. ml^–1), and mean biomass (biovolume) ranged between 0.215 and 0.372 mm³ l^–1 and between 0.586 and 1.223 mm³ respectively. In all, 332 algal taxa were identified: 298 in the upper section (Pantanal) and 143 in the middle and lower sections. They pertained to the Cyanophyta, Chlorophyta, Euglenophyta, Cryptophyta, Pyrrhophyta, Bacillariophyceae, Chrysophyceae and Xanthophyceae. Small Chlorophyta (Chloromonas gracilis, Choricystis minor, Crucigenia quadrata, Scenedesmus ecornis, Monoraphidium contortum and M. minutum) and Cryptophyta (Cryptomonas marssonii, C. ovata and Rhodomonas minuta) dominated. Bacillariophyceae (genera Aulacoseira and Cyclotella) increased in the lower section of the river. Biomass was dominated by centric forms of the genus Aulacoseira (A. granulata and its morphotypes, and A. herzogii). The diversity index varied between 1.99 and 5.0 bits ind.^–1 in winter and between 1.49 and 4.87 bits ind.^–1 in summer. Species richness (between 4 and 105 taxa per sample) showed a decrease in north–south direction. The presence of one of the largest wetlands of the world may explain the high algal diversity in the upper section. The Bermejo River, with highly mineralized waters and a high content of suspended solids, causes a strong discontinuity in the lower section of the main course, viz, a decrease in water transparency and in the density, biomass, diversity and species richness values of phytoplankton, before its waters meet the Paraná River.     

Nitrous oxide production by nitrogen-fixing,fast-growing Rhizobia

Rhizobium trifolii, R. leguminosarum, andR. hedysarum, grownex planta under anoxic conditions in a chemically defined medium, evolve N₂O from NO₃ ^–, NO₂ ^–, and (NH₄)₂NO₃. The amount of nitrous oxide formed after 96 hours is about 0.2M×mg^–1 cells d.w. Large availability of organic matter enhances the production of N₂O from nitrate by free-livingR. trifolii in peat/sand mixtures. Denitrification of the above species andR. meliloti was detected also in planta. Nitrous oxide production increases almost linearly from 10–45M×mg^–1 nodules d.w. when nitrogen-fixing plants are exposed to increasing concentrations of nitrate (1–12M).