Oxalic acid production and its role in pathogenesis of Sclerotinia sclerotiorum

Abstract Sunflower plants were inoculated with a virulent isolate of Sclerotinia sclerotiorum and with the same isolate nutritionally conditioned to produce small amounts of oxalic acid. The preconditioned isolate behaved as hypovirulent. Tomato plants were inoculated with four S. sclerotiorum isolates of increasing virulence. A close correlation among disease severity, accumulation of oxalic acid, decrease in pH and inhibition of polyphenoloxidase in both infected host tissues was demonstrated. Oxalic acid production as an important factor of virulence in S. sclerotiorum is emphasized and its effect on the phenolic metabolism of the host via inhibition of polyphenoloxidase is suggested.     

The Effect of Temperature on the Fatty Acid Composition of Tetrahymena pyriformis WH-14

SYNOPSIS. A reduction in the growth temperature of Tetrahymena pyriformis strain WH-14 from 35 C to 15 C resulted in distinct alterations in the fatty acid composition of the glycerophospholipids. The proportion of normal saturated acids declined from 26 to 19%; palmitoleic acid increased by 6%, and the composition of the polyunsaturated fatty acids increased in 18:2 Δ^6,11(n) and decreased in 18:2 Δ^9,12(n) and 18:3 Δ^6,9,12(n). The unsaturation index (the average number of double bonds/100 molecules) did not change with a shift in temperature.
Two biosynthetic pathways exist in Tetrahymena for the formation of unsaturated fatty acids. The observed changes in fatty acid composition that accompany a lowering of the environmental temperature can be accounted for by a reduction in the accumulation of products of the fatty acid pathway leading to the formation of γ-linolenic acid [16:0(n) → 18:0(n) → 18:1 Δ⁹(n) → 18:2 Δ^9,12(n) → 18:3 Δ^6,9,12(n)] and an increase in the components of the pathway leading to the formation of 18:2 Δ^6,11(n) [16:0(n) → 16:1 Δ⁹(n) → 18:1 Δ¹¹(n) → 18:2 Δ^6,11(n)]. The data suggest that the regulatory mechanism in Tetrahymena differs from that found in some bacteria where a simple substitution of unsaturated fatty acids for saturated fatty acids occurs at low culture temperatures.     

Protective effect of ions against cell death induced by acid stress in Saccharomyces

Saccharomyces boulardii is a probiotic used to prevent or treat antibiotic-induced gastrointestinal disorders and acute enteritis. For probiotics to be effective they must first be able to survive the harsh gastrointestinal environment. In this work, we show that S. boulardii displayed the greatest tolerance to simulated gastric environments compared with several Saccharomyces cerevisiae strains tested. Under these conditions, a pH 2.0 was the main factor responsible for decreased cell viability. Importantly, the addition of low concentrations of sodium chloride (NaCl) protected cells in acidic conditions more effectively than other salts. In the absence of S. boulardii mutants, the protective effects of Na⁺ in yeast viability in acidic conditions was tested using S. cerevisiae Na⁺-ATPases ( ena1-4 ), Na⁺/H⁺ antiporter ( nha1 Δ) and Na⁺/H⁺ antiporter prevacuolar ( nhx1 Δ) null mutants, respectively. Moreover, we provide evidence suggesting that this protection is determined by the plasma membrane potential, once altered by low pH and low NaCl concentrations. Additionally, the absence or low expression/activity of Ena proteins seems to be closely related to the basal membrane potential of the cells.     

Evidence for the synthesis of the multi-positional isomers of monounsaturated fatty acid in Methylococcus capsusatus by the anaerobic pathway

Abstract The biosynthesis of the positional isomers of the monounsaturated fatty acids of Methylococcus capsulatus (Bath) has been investigated by studying the incorporation of [2-¹⁴C]malonyl CoA into long-chain fatty acids in vitro. The major unsaturated products were Δ ⁹ 16:1 and Δ ¹¹ 18:1; however, Δ ⁸, Δ ¹⁰ and Δ ¹¹ 16:1, as well as, Δ ¹⁰, Δ ¹² and Δ ¹³ 18:1 were also synthesized. The exclusion of O₂ from the reaction vessel did not affect the synthesis of unsaturated fatty acids or the double bonds positions. Cerulenin inhibited the synthesis of unsaturated fatty acid more than saturated fatty acid. The use of both [1-¹⁴C] octanoate and [1-¹⁴C] decanoate as substrate resulted in the synthesis of long-chain fatty acids, however, unsaturates were only synthesized from octanoate. These results imply that the unique positional isomers of M. capsulatus are not synthesized by an aerobic mechanism.     

Nocturnal citrate accumulation and its response to environmental stress in the CAM plant Kalanchoe pinnata (Lam.) Pers.

Abstract. Kalanchoe pinnata (Lam.) Pers., a plant having crassulacean acid metabolism (CAM), was grown in high light (16–23 mol photons m⁻² d⁻¹) and in the shade (0.8–2.1 mol photons m⁻² d⁻¹), respectively. Plants were stressed in three ways, i.e. by transfer from high light to shade or vice versa just before measurements, and by withholding nitrogen and/or water. During the day-night cycle of CAM, K. pinnata showed day-night changes of citrate levels (Δ citrate) in addition to malate changes (Δ malate). Changes of leaf-cell sap osmotic pressure. Δπ, were linearly correlated with these changes of organic-acid anion levels with a relation of Δπ/(Δ citrate +Δ malate) = 1/1. The environmental stressor, i.e. limited N-nutrition, drought and higher or lower irradiance than experienced during growth, affected the absolute and relative contributions made by Δ citrate and Δ malate to total nocturnal organic-acid accumulation. In the high-light-grown plants transferred to the shade, changes of citrate levels were much less affected than changes of malate levels by the generally decreased metabolic activity and inhibition of CO₂ uptake. In the shade-grown plants, Δ citrate increased in response to stress imposed by interactive effects of the three stressors.     

Comparison of some decontamination methods and growth media for isolation of mycobacteria from northern brook waters

Two decontamination methods and five media were compared for the isolation of mycobacteria from brook waters of different physical, chemical and bacteriological characteristics. The decontaminants used were: 0.7 mol 1^-1 NaOH followed by 50 g 1^-1 oxalic acid and 0.9 mol 1^-1 H₂SO₄ combined with 0.5 g 1^-1 cycloheximide. The media compared were: Mycobacteria 7H11 agar with OADC enrichment (pH 6.6), glycerol egg (pH 6.5 and 5.5), and pyruvate egg (pH 6.5 and 5.5). All media contained cycloheximide, 0.5 g 1^-1. The NaOH—oxalic acid method generally resulted in lower contamination and higher isolation of mycobacteria than the H₂SO₄-cycloheximide method. With the NaOH—oxalic acid method, all five media were equal in positivity rates but contamination was a problem on Mycobacteria 7H11 agar. Of the four egg media tested, the highest positivity rate (92% of the samples) was obtained on the pyruvate modification (pH 6.5), and the highest mean colony count of mycobacteria (900 cfu 1^-1) on the glycerol modification (pH 6.5). Characteristics of water and sampling site had similar effects on the isolation frequencies of mycobacteria obtained by different combinations.     

Ecological genetics of the Adh-1 locus of Drosophila buzzatii

The Adh-1 polymorphism of Drosophila buzzatii was studied in terms of the effects of the larval substrate (laboratory food and Opuntia stricta tissue inoculated with live yeast species) on larval survival, development time and subsequent adult size, using the three common Adh-1 genotypes. Studies with laboratory food yielded mixed results, but in general the Adh-1^b/Adh-1^b genotype was superior to Adh-1^c/Adh-1^c with the heterozygote intermediate. Studies with the natural substrate (Opuntia stricta tissue) using mono- and bicultures of four associated yeast species also showed that the Adh-1^b/Adh-1^b genotype develops faster and survives better than Adh-1^c/Adh-1^c. There were no genotype-by-yeast interactions which might explain the maintenance of the polymorphism. Drosophila buzzatii larvae develop faster and attain larger adult sizes when raised on bicultures of yeasts as compared with the corresponding monocultures.     

Na+-driven ATP synthesis of a psychrophilic marine bacterium, Vibrio sp. strain ABE-1

Abstract: In vivo ATP synthesis of a psychrophilic marine bacterium, Vibrio sp. strain ABE-1, derived from endogenous respiration, was examined. ATP was synthesized at both pH 6.5 and 8.5 after the start of the endogenous respiration by supplying O₂ to the anaerobic cell suspension. The ATP synthesis at pH 6.5, but not at pH 8.5, was completely inhibited by a H⁺ conductor, carbonylcyanide m -chlorophenylhydrazone (CCCP). The CCCP-resistant ATP synthesis at pH 8.5 was strongly inhibited by an inhibitor of the respiration-dependent primary Na⁺ pump, 2- n -heptyl-4-hydroxyquinoline N -oxide, and essentially required Na⁺. These results show that this bacterium synthesizes ATP at pH 6.5 by electrochemical potentials across the membrane Δ ∼ μ _H+, whereas at pH 8.5 by Δ ∼ μ _Na+ but not Δ ∼ μ _H+.     

High-yield production of oxalic acid for metal leaching processes by Aspergillus niger

Abstract The complex-forming compound oxalic acid can effectively solubilise metals such as aluminium, iron, lithium, and manganese. In order to produce high amounts of oxalic acid for biohydrometallurgical processes, it was the aim of this work to optimise oxalic acid production by Aspergillus niger , a fungus well known for its ability to produce oxalic acid. A. niger excreted 427 mmol oxalic acid 1⁻¹ if it was cultivated in a pH-controlled (pH 6.0) fed-batch run in a 2-1 stirred tank reactor. Sucrose and lactose permeate were suitable carbon sources for oxalic acid production. In sucrose medium, A. niger produced high amounts of gluconic and oxalic acids, whereas in lactose permeate medium only oxalic acid was produced. Cultivation in green syrup and molasses media lead to high yields of biomass, but low oxalic acid production (<20 mmol 1⁻¹).     

Evidence for the Tf locus being associated with an early lethal factor in a strain of pigs

The frequencies of three co-dominant alleles Tf ^A, Tf ^B and Tf ^c controlling the serum transferrin locus in native and exotic breeds of pig in the United Kingdom are shown. Matings between different transferrin genotypes and segregation of the transferrin alleles in piglets from 131 litters are also recorded.
In eleven litters from matings within a closely related group of animals heterozygous for the Tf ^c allele, no offspring of the Tf ^c/ Tf ^c genotype were born. Matings between heterozygous related boars believed to be carrying a lethal factor linked to the Tf locus and heterozygous unrelated sows of the Saddleback breed, resulted in offspring of the Tf ^c/ Tf ^c genotype being born.
An excess of heterozygote genotypes was found in all litters from matings between animals heterozygous for the Tf ^c allele. In all these litters the average litter size was 0.5 piglets less per litter than the average for all other litters studied. For the eleven litters from matings involving closely related animals heterozygous for the Tf ^c allele, the average litter size was 1.4 piglets less per litter than the average for all other litters.
The possibility of an early lethal factor being linked to the Tf locus in this family of pigs is discussed.     

Effects of amiodarone on K+, internal pH and Ca2+ homeostasis in Saccharomyces cerevisiae

In this study, amiodarone, at very low concentrations, produced a clear efflux of K⁺. Increasing concentrations also produced an influx of protons, resulting in an increase of the external pH and a decrease of the internal pH. The K⁺ efflux resulted in an increased plasma membrane potential difference, responsible for the entrance of Ca²⁺ and H⁺, the efflux of anions and the subsequent changes resulting from the increased cytoplasmic Ca²⁺ concentration, as well as the decreased internal pH. The Δ tok1 and Δ nha1 mutations resulted in a smaller effect of amiodarone, and Δ trk1 and Δ trk2 showed a higher increase of the plasma membrane potential. Higher concentrations of amiodarone also produced full inhibition of respiration, insensitive to uncouplers and a partial inhibition of fermentation. This phenomenon appears to be common to a large series of cationic molecules that can produce the efflux of K⁺, through the reduction of the negative surface charge of the cell membrane, and the concentration of this cation directly available to the monovalent cation carriers, and/or producing a disorganization of the membrane and altering the functioning of the carriers, probably not only in yeast.     

pH homeostasis and bioenergetic work in alkalophiles

Abstract A Na⁺/H⁺ antiporter catalyses coupled Na⁺ extrusion and H⁺ uptake across the membranes of extremely alkalophilic bacilli. This exchange is electrogenic, with H⁺ translocated inward > Na⁺ extruded. It is energized by the Δψ ² component of the ΔμH⁺ that is established during primary proton pumping by the alkalophile respiratory chain complexes. These complexes abound in the membranes of extreme alkalophiles. Combined activity of the respiratory chain, the antiporter, and solute transport systems that are coupled to Na⁺ re-entry, allow the alkalophiles to maintain a cytoplasmic pH that is several pH units more acidic than optimal external pH values for growth. There is no compelling evidence for a specific and necessary role for any ion other than sodium in pH homeostasis, and although there is very high cytoplasmic buffering capacity in the alkaline range, active mechanisms for pH homeostasis are crucial. Energization of the antiporter as well as the proton translocating F ₁ F ₀-ATPase that catalyses ATP synthesis in the extreme alkalophiles must accommodate the problem of the low net ΔμH⁺ and the very low concentrations of protons, per se, in the external medium. This problem is by-passed by other bioenergetic work functions, such as solute uptake or motility, that utilize sodium ions for energy-coupling in the place of protons.     

Demonstration of a K+/H+ exchange activity in a photodenitrifier, Rhodopseudomonas sphaeroides forma sp. denitrificans

Abstract Washed cells of Rhodopseudomonas sphaeroides forma sp. denitrificans , grown under photodenitrifying conditions, exhibited K⁺ uptake dependent on the transmembrane proton gradient (Δ pH). These cells also acidified the suspension medium in response to K⁺ pulses both aerobically and anaerobically in light and in the dark. The results indicate that the photodenitrifier has a reversible K⁺/H⁺ exchange activity which reflects its role in regulating the intracellular K⁺ concentration, as well as intracellular pH. The acidification of the external medium resulting from K⁺ pulses was inhibited by carbonyl cyanide- m -chlorophenylhydrazone (CCCP) indicating that the antiporter is energy-dependent. Addition of KCl to washed cells depolarized the membrane potential (Δψ) with a concomitant increase in ΔpH, indicating that the K⁺/H⁺ antiporter was electrogenic.     

Studies on the transferrins of goats. 3. Evidence for a third transferrin allele

A new allele Tf ^c in serum transferrin of goats is postulated. It was considered that serum transferrins in goats classified into six phenotypes are genetically controlled by three codominant alleles, Tf ^A, Tf ^B and Tf ^c. Frequencies of Tf ^c were low in native goats in Korea, Philipines and Thailand, and this allele is yet to be observed in other breeds of goats.     

Gas exchange and carbon isotope composition of Ananas comosus in response to elevated CO2 and temperature

Ananas comosus L. (Merr.) (pineapple) was grown at three day/night temperatures and 350 (ambient) and 700 (elevated) μ mol mol^–1 CO₂ to examine the interactive effects of these factors on leaf gas exchange and stable carbon isotope discrimination ( Δ ,‰). All data were collected on the youngest mature leaf for 24 h every 6 weeks. CO₂ uptake (mmol m^–2 d^–1) at ambient and elevated CO₂, respectively, were 306 and 352 at 30/20 °C, 175 and 346 at 30/25 °C and 187 and 343 at 35/25 °C. CO₂ enrichment enhanced CO₂ uptake substantially in the day in all environments. Uptake at night at elevated CO₂, relative to that at ambient CO₂, was unchanged at 30/20 °C, but was 80% higher at 30/25 °C and 44% higher at 35/25 °C suggesting that phosphoenolpyruvate carboxylase was not CO₂-saturated at ambient CO₂ levels and a 25 °C night temperature. Photosynthetic water use efficiency (WUE) was higher at elevated than at ambient CO₂. Leaf Δ -values were higher at elevated than at ambient CO₂ due to relatively higher assimilation in the light. Leaf Δ was significantly and linearly related to the fraction of total CO₂ assimilated at night. The data suggest that a simultaneous increase in CO₂ level and temperature associated with global warming would enhance carbon assimilation, increase WUE, and reduce the temperature dependence of CO₂ uptake by A. comosus .     

Effect of environmental factors and precursors on oxalic acid production,mycelial biomass and virulence of a potential bioherbicide isolate of Sclerotium rolfsii SC64 produced in liquid culture

The fungus Sclerotium rolfsii is presently under development as a bioherbicide for broadleaf weed species using fungus-infested substrates as application material in this laboratory. The effect of environmental factors and three precursors (citric acid, ascorbic acid, and sodium succinate) on mycelial growth, oxalic acid production, and virulence by SC64 in liquid culture were investigated. The results showed that for mycelia growth the optimum liquid medium was Modified Richard's solution (MRS) among the five tested media, but potato dextrose broth (PDB) produced the maximum oxalic acid production and virulence on detached Solidago canadensis leaves. When PDB was used as the basic medium, the oxalic acid/mycelial dry weight (mg g^–1) ratio reached the peak 4 days after inoculation. The optimum temperature for oxalic acid production was at 27°C, but increased mycelial dry weight and virulence were observed at 30°C. The optimum range of initial pH value for oxalic acid accumulation was 4.0–6.0, with the optimal pH 5.0; highest mycelial growth was with an initial pH 3.5–6.0 (optimum pH 5.0) and subsequently pH 3.5–5.5 (maximum at pH 3.5). Both mycelial dry weight and oxalic acid production showed a decreasing trend as a result of the precursor of oxalic acid being added to PDB. Among the three precursors, the greatest decrease in mycelial dry weight, and oxalic acid production was caused by sodium succinate. This clarification of optimal conditions for production of mycelial biomass while insuring high concentrations of oxalic acid and high virulence should be useful for further development of this fungus as biocontrol agent.