Direct Evidence for Changes in the Resistance of Legume Root Nodules to O2 Diffusion

Indirect evidence suggests that legumes can adjust rapidly theresistance of their root nodules to O₂ diffusion. Here we describeexperiments using O₂ specific micro-electrodes and dark fieldmicroscopy to study directly the operation of this diffusionbarrier. The O₂ concentration sensed by the electrode decreasedsharply in the region of the inner cortex and was less than1.0 mmol m^–3 throughout the infected tissue in nodulesof both pea (Pisum sativum) and french bean (Phaseolus vulgaris).In a number of experiments the ambient O₂ concentration wasincreased to 40% while the electrode tip was just inside theinner cortex. In 13 out of 21 cases the O₂ concentration atthis position either remained low and unchanged or increasedirreversibly to near ambient values. In the remaining casesthe O₂ concentration increased after 1 to 2.5 min and then decreasedto its former value. These results are ascribed to an increasein resistance of the barrier in response to increased O₂ fluxinto the nodule. It was shown microscopically that air spacesboth at the boundary between the infected zone and the innercortex, and within the infected zone started to disappear 3min after nodules were exposed to high ambient O₂ concentrationsand had disappeared completely after 8 min. These spaces werenot changed by exposure of the nodule for 10 min to either N₂or air. Key words: Oxygen, root nodules, air spaces     

Evolution of the 28S ribosomal RNA gene in anurans: regions of variability and their phylogenetic implications

Fifteen restriction sites were mapped to the 28S ribosomal RNA gene of individuals representing 54 species of frogs, two species of salamanders, a caecilian, and a lungfish. Eight of these sites were present in all species examined, and two were found in all but one species. Alignment of these conserved restriction sites revealed, among anuran 28S rRNA genes, five regions of major length variation that correspond to four of 12 previously identified divergent domains of this gene. One of the divergent domains (DD8) consists of two regions of length variation separated by a short segment that is conserved at least throughout tetrapods. Most of the insertions, deletions, and restriction-site variations identified in the 28S gene will require sequence-level analysis for a detailed reconstruction of their history. However, an insertion in DD9 that is coextensive with frogs in the suborder Neobatrachia, a BstEII site that is limited to representatives of two leptodactylid subfamilies, and a deletion in DD10 that is found only in three ranoid genera are probably synapomorphies.      

Abnormalities of the erythrocyte membrane in chronic myelogenous leukemia

Chronic myelogenous leukemia (CML) is a hematologic malignancy characterized by excessive growth of myeloid cells and their progenitors. The proportion of spectrin dimers compared to tetramers extracted from membranes at 4 degrees C, under low ionic strength conditions, increased in CML erythrocytes. These also displayed abnormal thermal sensitivity (between 45 and 46 instead of 49 degrees C). Crosslinking with the bifunctional reagent, dimethyl adipimidate (8.6 A) showed significant organizational modification of not only spectrin, but other cytoskeletal components such as ankyrin, bands 4.2 and 5. Enhanced concanavalin A (Con-A) agglutinability of CML erythrocytes also suggests altered topographic distribution of a functionally important membrane protein, band 3. The anion transport activities of erythrocytes from patients with CML and normal donors were comparable. In CML erythrocytes, significant reduction in the number of ankyrin-binding sites, present in the cytoplasmic domain of band 3, may lead to partial loss of cytoskeletal anchorage to the bilayer and account for their increased Con-A agglutinability and heat sensitivity and may lead to their premature removal from the circulation.     

Studies on RTD and continuous culture (SCP) in cylindrical and tapered reactors

The performance of a tapered reactor for the continuous cultivation of bakers' yeast (SCP) from cane molasses has been compared with that of a conventional cylindrical reactor. It is found that the tapered reactor has less non-idealities (bypass and deadspace).Using the experimentally evaluated bypass and deadspace values, a model for predicting conversions of substrate (cane molasses), based on the RTD model proposed by Cholette and Cloutier has been developed. The experimental substrate conversions are found to match the model satisfactorily.List of Symbols D h^–1 dilution rate - E() exit age distribution function - K _s kg/m³ Monod's saturation constant - -r _sa kg/(m³ · h) rate of substrate utilization - S kg/m³ substrate concentration expressed as dextrose equivalent (DE) - S _a kg/m³ substrate concentration in active zone - S ₀ kg/m³ initial substrate concentration - S/S ₀ dimensionless substrate concentration - v _a dm³/h volumetric flow through active zone - v _b dm³/h volumetric flow through bypass stream - u _l dm³/h substrate feed rate - v _g dm³/min air-flow rate - V dm³ total working volume of the reactor - V _a dm³ volume of active zone in reactor - V _d dm³ volume of dead zone in reactor - X kg/m³ biomass concentration Greek Letters fraction of bypass of feed, v _b /v _l - fraction of deadspace, V _d /V - dimensionless residence time - _m h^–1 maximum specific growth rate - h mean residence time, V/v _l      

Optimal control strategy for the enhanced production of cellulase enzyme using the new mutant Trichoderma reesei E-12

Cellulase enzyme production was enhanced using the mutant strain Trichoderma reesei, E-12, which was shown to be partially resistant to catabolite repression. An optimal profile for pH, which was found to be the critical environmental parameter, was determined using a rigorous mathematical optimization procedure. Semi-empirical models were used to minimize complications in the computation. A 30% increase in enzyme activity and productivity was obtained using the optimal pH strategy as compared to the pH cycling strategy.List of Symbols a ₁ , a ₂ , a ₃ d^–1, d^–2, d^–3 coefficients of the polynomial in the generalized logistic growth model - a ₄, a ₅, a ₆ d^–1, d^–2, d^–3 coefficients of the polynomial in the generalized logistic product model - b ₁ d^–1 enzyme synthesis rate constant - b ₂ d ^–1 enzyme decay rate constant - b ₃ power coefficient in the polynomial model for enzyme synthesis - H Hamiltonian function - J Objective function of the maximization procedure - K ₁ kg/m³ limiting cell mass concentration in biomass logistic model - K _s kg/m³ saturation constant - K ^s kg/m³ saturation death rate constant - q power coefficient in polynomial model - s kg/m³ substrate concentration - t d fermentation time - T d total fermentation time (=7 d) - x ₁₀ kg/m³ initial biomass concentration - x ₁ kg/m³ biomass concentration at time t - x ₂ F.P.A enzyme activity at time t - x ₃ d state variable replacing time term on the right hand side of biomass equation - x _f kg/m³ final biomass concentration - z ₁, z ₂, z ₃ adjoint variable corresponding to state variable x ₁, x ₂, x ₃ - d^–1 specific death rate - d^–1 specific growth rate     

Effect of carbon sources on the synthesis of pectinase by Aspergilli

The synthesis of pectinase is investigated using six species of Aspergillus, with five media differing either in their carbon sources or level of carbon source(s). Five of the six species used, synthesized appreciable amounts of pectinase in the media containing sugars. Pectinase synthesis was highest for A. niger, NCIM 548, with all the sugar containing media. A. foetidus, NCIM 510, was the only one among the organisms studied, that responded well to the medium containing pectin in the absence of additional sugars supplied in the medium.     

A fed batch surface culture process for the production of citric acid with reuse of Aspergillus niger mycelia

Citric acid production in surface culture process with reuse of mycelia for more than one batch of media has been reported in this work. A strategy for replacing media and thus increasing productivity in subsequent batches is discussed. An explanation for the decrease in citric acid accumulation beyond the second batch is suggested on the basis of oxygen limitation.     

Ethanol separation by selective adsorption of water

Preferential adsorption of water in the vapor phase by lignocellulosic residues for the production of anhydrous ethanol has been reported in this work. Rice straw, microcrystalline cellulose powder (MCCP) and bagasse were the lignocellulosic residues used as adsorbents. Starting with an ethanol concentration of 80–90% a final concentration above the azeotropic concentration was obtained. An energy analysis of the process was made and a possible explanation of phenomena suggested.     

Optimization of carbon and nitrogen sources in the medium and environmental factors for enhanced production of chitinase by Trichoderma harzianum

Statistical design was used to determine the optimal levels of medium components, the optimal initial pH of the enzyme production medium, the temperature of fermentation, age of the organism in the slant growth and the age of the inoculum for the production of chitinase in shake flask fermentations. The use of high concentrations of chitin and ammonium sulphate and exclusion of peptone and urea from the medium resulted in the production of higher level of the enzyme. The optimal concentrations of the medium components were 12.5 kg/m³ and 4.2 kg/m³ for the chitin and ammonium sulphate respectively. The effect of the addition of peptone and urea to the optimized medium was studied. The optimal values of initial pH and temperature were 5.6 and 28 °C respectively. The optimal age of the slant and the inoculum were found to be 105 h and 43 h respectively. The highest level of chitinase before optimization of the above variables was 0.054 U which was maximized to the level of 0.197 U.     

Parameters optimization of chitin hydrolysis by Trichoderma harzianum chitinase under assay conditions

A kinetic analysis and optimization of reaction conditions for the enzymatic hydrolysis of chitin using chitinase produced by Trichoderma harzianum NCIM 1185 was carried out. Swollen chitin was used as the substrate for chitinase. The central composite design was followed for this optimization. The required volume ratio of the major reactants for maximum hydrolysis was determined. The pH and temperature optima were found to be 4.75 and 47 °C respectively. K _m and V _max for this enzyme were 4.643 kg/m³ and 0.1542 U respectively.