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A L Demain

Publications and source records attributed to A L Demain.

At least 145 records · Page 8Linked to original sources
PubMed1979

Nutritional Studies on Xanthan Production by Xanthomonas campestris NRRL B1459.

The nutritional requirements of Xanthomonas campestris NRRL B1459 for optimal xanthan production were studied in a chemically defined medium. Of the carbon sources tested, a 4% sucrose or glucose medium yielded the highest xanthan titers. The further addition of certain organic acids, such as succinate, pyruvate, and alpha-ketoglutarate, stimulated xanthan production; excess concentrations of these organic acids inhibited xanthan formation. Certain amino acids (e.g., glutamate) and nitrate salts were superior to ammonium salts for xanthan production. Concentrations of these nitrogen sources higher than the optimal levels inhibited xanthan production while stimulating growth. Xanthan production was also sensitive to high concentrations of inorganic phosphate. High xanthan potencies, up to 30 g/kg of broth, were achieved in these shake-flask studies, in which completely defined media were used.

Journal Article↗
PubMed1979

Nitrogen nutrition and regulation of cephalosporin production in Streptomyces clavuligerus.

When used as sole nitrogen source, certain amino acids (e.g., proline, asparagine) supported both growth and sporulation by Streptomyces clavuligerus streaked onto solid defined medium. Ammonium supported growth but suppressed sporulation. Amino nitrogen was best for cephalosporin production in liquid defined medium, although urea was almost as useful. A comparison of amino acids showed asparagine and glutamine to be the best nitrogen sources and arginine to be almost as good. Ammonium salts supported a somewhat lower growth rate than asparagine, but antibiotic production was very poor on these inorganic nitrogen sources. Addition of ammonium to asparagine did not affect growth rate but increased mycelial mass; cephalosporin production was reduced by about 75%. Antibiotic production was more closely associated with growth in the absence of ammonium than in its presence, indicating a strong inhibitory and (or) repressive effect of NH4+ on antibiotic production. Ammonium exerted its negative effect when added at 24h or earlier, i.e. before antibiotic formation began.

Amino Acids↗
PubMed1979

Further studies on microbiological ring-expansion of penicillin N.

The rate of microbiological ring-expansion of penicillin N to deacetoxycephalosporin C using protoplast lysates of the antibiotic-negative mutant Cephalosporium acremonium M-0198 has been increased some 70-fold over that of our earlier system. We confirmed the stimulatory effects of FeSO4 and ascorbate described by Hook et al. (Biochem. Biophys. Res. Commun. 87: 258, 1979); the optimum concentrations found were 0.04 mM FeSO4 and 0.67 mM ascorbate. Adenosine triphosphate concentration was lowered to 0.83 mM; phosphoenolpyruvate and pyruvate kinase were eliminated. The optimum pH and temperature for the reaction were 7.2 and 25 degrees C, respectively. Alpha-ketoglutarate and MnCl2 showed no marked effect on the reactions, MgSO4 and KCl were mildly stimulatory, and CuSO4 and ZnSO4 were very inhibitory. Penicillin N was optimal at a concentration of 0.07 mM. Specific ring-expansion activity reached its peak 13 hours after growth ceased and then disappeared rapidly.

Acremonium↗
PubMed1979

Aminoglycosides, genes and regulation.

A major role has been played by aminoglycoside research in the development of fermentation science especially involving genetics and regulation. The first report of the use of an antibiotic to select high producers of that antibiotic was done with the streptomycin producer. Mutational biosynthesis of new antibiotics originated with studies on the neomycin producer. The first demonstration of the presence of genes coding for antibiotic inactivation in antibiotic producers was made with Streptomyces griseus, the producer of streptomycin. Induction of an enzyme involved in secondary metabolism was found first with mannosidostreptomycinase. The first example of a nonprecursor molecule which could induce an entire antibiotic biosynthetic pathway was A-Factor involved in streptomycin production. Glucose repression and amino acid repression of mannosidostreptomycinase were the first examples of carbon catabolite repression and nitrogen metabolite repression respectively of an enzyme involved in secondary metabolism. Data supporting the occurrence of nitrogen metabolite regulation of antibiotic biosynthesis were first gathered in the early days of development of the streptomycin fermentation when it was found that the slowly used soybean meal and proline were the best nitrogen sources for antibiotic production. Aminoglycoside research also provided the first explanation of a mechanism of phosphate control of antibiotic biosynthesis. The first indication that antibiotic formation is not obligatory for spore formation was provided by data on streptomycin production.

Aminoglycosides↗
PubMed1978

Uptake and metabolism of alpha-aminoadipic acid by Penicillium chrysogenum Wis 54-1255.

The uptake of 1-14C-DL-alpha-aminoadipate in resting mycelium of Penicillium chrysogenum Wis 54-1255 and its metabolism during benzylpenicillin formation were studied. The pH optimum for uptake at 25 degrees C was 6.4. Over a range of concentrations from 0.01--1.0 mM, approximately 45% of 1-14C-DL-alpha-aminoadipate was taken up by carbon-starved mycelium. 14CO2 was formed at a low rate, and the total formed amounted to only 1--3% of the 1-14C-DL-alpha-aminoadipate supplied. The intracellular pool of alpha-aminoadipate appears to be expandable, depending on the concentration of alpha-aminoadipate in the medium. The rate of penicillin synthesis depended on the intracellular concentration of alpha-aminoadipate. Penicillin biosynthesis achieved half of the maximum rate at an intracellular concentration of 0.06 nmol alpha-aminoadipate/mg dry cell weight. This low concentration, the result of adding 0.01 mM DL-alpha-aminoadipate to the medium, was sufficient to reverse the inhibition of penicillin biosynthesis caused by 10 mM extracellular L-lysine. Aminoadipate appears to be recycled during penicillin formation. Labeled alpha-ketoadipate was formed from alpha-aminoadipate to the extent of about 25%.

2-Aminoadipic Acid↗
PubMed1978

Cell-free ring expansion of penicillin N to deacetoxycephalosporin C by Cephalosporium acremonium CW-19 and its mutants.

To examine microbiological ring expansion of penicillin N to a cephalosporin, we obtained five mutants of Cephalosporium acremonium blocked in beta-lactam antibiotic biosynthesis from 2500 survivors of mutagenesis. In submerged fermentation, mutants M-0198, M-0199, and M-2351 produced no beta-lactam antibiotic (type A), whereas mutants M-1443 and M-1836 formed penicillin N but not cephalosporin C (type B). Cell-free extracts of type A mutants converted penicillin N to a cephalosporin; those of type B mutants did not. The product of the cell-free reaction was identified as deacetoxycephalosporin C by thin-layer chromatography, paper chromatography, paper electrophoresis, and enzyme tests. These data strongly support our hypothesis that penicillin N is an intermediate of cephalosporin biosynthesis.

Acremonium↗
PubMed1978

Carbon catabolite regulation of cephalosporin production in Streptomyces clavuligerus.

Cephalosporin production by Streptomyces clavuligerus is regulated by some type of carbon catabolite control. Increasing concentrations of preferred carbon sources, such as glycerol and maltose, decreased production of the antibiotics. Poorer carbon sources, such as alpha-ketoglutarate and succinate, led to high specific production of cephalosporins and shifted the dynamics of fermentation to a greater degree of association with growth. The results support the concept that the phase in which a product is made by a microorganism is not a function of the particular molecule produced, but rather of the nutritional environment presented to the organism.

Amino Acids↗
PubMed1978

Tryptophan excretion by a bradytroph of Hansenula polymorpha growing in methanol.

The growth of a bradytrophic mutant isolated from the methanol-utilizing yeast Hansenula polymorpha was found to be stimulated by both tyrosine and phenylalanine. The mutant contained about half as much chorismate mutase activity as the wild-type strain. When grown in a medium containing 2% mehtanol as the major carbon and energy source, the bradytroph excreted a low but significant level (28 mg/liter) of L-tryptophan.

Ascomycota↗
PubMed1978

Production of luteoskyrin and isolation of a new metabolite, pibasterol, from Penicillium islandicum Sopp.

Production of luteoskyrin, a hepatotoxin synthesized by Penicillium islandicum Sopp., was studied with various fermentation methods. Best results were obtained in static fermentations on glutinous rice at 30 degrees C. The isolated yield of pure luteoskyrin was approximately 400 mg per kg of rice. Also produced were skyrin, islandicin, iridoskyrin, rubroskyrin, chrysophanol, mannitol, and erythritol. A new metabolite, which we call pibasterol, was also isolated.

Anthraquinones↗
PubMed1978

Production of cyclochlorotine and a new metabolite, simatoxin, by Penicillium islandicum Sopp.

Production of the hepatotoxin cyclochlorotine by Penicillium islandicum was studied under a variety of fermentation conditions. The best system for production was agitated red wheat. A thin-layer chromatographic method was developed for the detection of this cyclic polypeptide. These experiments have resulted in the isolation of a new toxic metabolite, which we call simatoxin.

Animals↗
PubMed1978

Mollicellins: mutagenic and antibacterial mycotoxins.

Eight mollicellins (depsidones) were assayed for mutagenicity and antibacterial activity in Salmonella/microsome tests involving histidine reversion and forward mutation to 8-azaguanine resistance. Two of them, mollicellins C and E, which contain a 3-methylbutenoic acid moiety, were mutagenic and bactericidal for Salmonella typhimurium in the absence of microsomes. Mollicellins D and F, each containing a chlorine atom, were bactericidal but not mutagenic. The mutagenic activity was completely abolished and the antibiotic activity was greatly reduced by coincubation with rat liver microsomes.

Animals↗
PubMed1977

Influence of inorganic phosphate and organic buffers on cephalosporin production by Streptomyces clavuligerus.

A high concentration of potassium phosphate (75--100 mM) stabilized pH and supported extensive growth of Streptomyces clavuligerus in a chemically defined medium; such a concentration also inhibited cephalosporin production. Although Tris buffer was found to have detrimental effects on growth and antibiotic production, 3-(N-morpholine)-propane sulfonate (MOPS) or 2-(NP-morpholine)-ethane sulfonate (MES) buffer provided a nontoxic buffering system. In the presence of MOPS buffer, cephalosporin production was optimal at 25 mM phosphate, whereas higher concentrations of phosphate progressively inhibited antibiotic production up to 85% without modifying the pH pattern. MOPS buffer can be used to conduct fermentations at a relatively constant pH value in shake flasks.

Alkanesulfonates↗
PubMed1977

Regulation of extracellular protease production in Candida lipolytica.

Production of extracellular protease by Candida lipolytica NRRL Y-1094 was derepressed upon transfer to carbon-, nitrogen- or sulphur-free medium but not upon transfer to phosphorus-free medium. The protease activities produced under the three nutrient limitations had alkaline pH optima and similar substrate and inhibitor specificities. Any one of the following three conditions was found to be sufficient for derepression of extracellular protease: (a) "poor" carbon source, (b) cysteine intracellular pool below 0.5 micronmol/g dry weight cells and (c) ammonia intracellular pool below 10 micronmol/g dry weight cells. Thus, extracellular protease production in C. lipolytica was subject to at least three different regulatory controls, carbon, sulphur and nitrogen repression. Intracellular cysteine and ammonia appeared to be the metabolic signals for sulphur and nitrogen repression, respectively. Anabolic glutamate dehydrogenase did not act as a regulatory protein mediating nitrogen repression. Exogenous protein had an inductive effect on extracellular protease production.

Ammonia↗
PubMed1977

Studies on the cell-free biosynthesis of beta-lactam antibiotics.

Cell walls of Cephalosporium acremonium mycelia were lysed by enzyme preparations from either Helix pomatia (snail) digestive juice or Cytophaga. The yield of protoplasts depended on the lytic-enzyme preparation and the age of the culture, and it increased after the mycelia were pretreated with dithiothreitol. A cell-free preparation, obtained by osmotic lysis of protoplasts, synthesized labelled penicillin N from L-[14C]valine. Approx. 0.03-0.06% of the amino acid was incorporated into penicillin N. Under conditions of penicillin N synthesis, the broken-protoplast preparation failed to produce significant amounts of cephalosporin C or its precursors, deacetylcephalosporin C and deacetoxycephalosporin C.

Acremonium↗