Differential sensitivities to glucose and galactose repression of gluconeogenic and respiratory enzymes from Saccharomyces cerevisiae

The synthesis of isocitrate lyase was induced by the presence of ethanol in the chemostat reaching a specific activity of 200 mU·mg^-1 at this induced state. In glucoselimited, derepressed cells, 20 mU·mg^-1 were detected and under repressed conditions isocitrate lyase activity was not detected.The sensitivity of gluconeogenic enzymes: cytoplasmic malate dehydrogenase; fructose 1,6-bisphosphatase and isocitrate lyase as well as the mitochondrial enzymes NADH dehydrogenase and succinate cytochrome c oxidase to glucose and galactose repression were studied in chemostat cultures. Our results show that galactose was less effective as a repressor than glucose. Malate dehydrogenase was completely inactivated by glucose, whereas galactose only produced a 78% decrease of specific activity. Fructose 1,6-bisphosphatase and isocitrate lyase were completely inactivated by both sugars but at different rate. Glucose produced an 85% decrease of specific activity of the mitochondrial enzymes whereas galactose only decrease an 67%.     

The influence of the culture pH value on the direct glucose oxidative pathway in Klebsiella pneumoniae NCTC 418

Klebsiella pneumoniae NCTC 418 was cultured aerobically in chemostat cultures (D=0.3 h^-1; 35°C) under respectively carbon-, phosphate-, potassium-, sulphate-, and ammonia-limited conditions with glucose as the sole carbon and energy source. The effect of the external pH value on glucose metabolism and on the enzymes of the direct glucose oxidative pathway was examined. The pH value of the medium had a profound influence on both the activity and the synthesis of the glucose dehydrogenase and the gluconate dehydrogenase. At pH values ranging from pH 5.5 to pH 6.0 maximal activity and synthesis of these enzymes resulted in a more than 80% conversion of the glucose consumed into gluconate and 2-ketogluconate under potassium-or phosphate-limited conditions. On the other hand, no gluconate and/or 2-ketogluconate production could be detected when K. pneumoniae was cultured at pH 8.0. Whereas the synthesis of gluconate dehydrogenase seemingly was completely repressed, still some glucose dehydrogenase was present. The lack of glucose dehydrogenase activity at pH 8.0 was shown not to be due to the dissociation of the cofactor PQQ from the enzyme.Abbreviations DCIP dichlorophenol indophenol - PQQ pyrroloquinoline quinone [2,7,9-tricarboxy-1H-pyrrolo (2,3-f) quinoline-4,5-dione] - WB Wurster's Blue [1,4-bis-(dimethylamino)-benzene perchlorate]     

Isolation and characterization of yeast mutants defective in intermediary carbon metabolism and in carbon catabolite derepression

Summary Yeast mutants deficient in the constitutive ADHI (adc1) were used for the isolation of mutants with deficiencies of the intermediary carbon metabolism, and of mutants defective in carbon catabolite derepression. Mutants were recognized by their inability to grow on YEP-glycerol and/or on ethanol synthetic complete medium. They were either defective in isocitrate lyase (icl1), succinate dehydrogenase (sdh1), or malate dehydrogenase (mdh1, mdh2), mdh-mutants could not uniformely be appointed to one of the known MDH isozymes. Homozygous mdh and sdh1 diploids are unable to sporulate.Three gene loci could be identified by mutants pleiotropically defective in many or all of the enzymes tested. In ccr1 mutants, derepression of isocitrate lyase, fructose-1,6-diphosphatase, ADHII and possibly of the cytoplasmic MDH is prevented, whereas the mitochondrial TCA-cycle enzymes, succinate dehydrogenase and malate dehydrogenase, are not significantly affected. CCR2 and CCR3 have quite similar action spectra. Both genes are obviously necessary for derepression of all enzymes tested. It could be shown that ccr1, ccr2 and ccr3 mutants are not respiratory deficient.     

A further characterization of the cinnamon gene in Drosophila melanogaster

Summary Two mutants of Saccharomyces cerevisiae lacking pyruvate kinase (EC.2.7.1.40) are described. The mutations are recessive, segregate 2⁺:2^- in tetrads and do not complement each other. Single-step spontaneous revertants, isolated on glucose plates, get back pyruvate kinase activity. The enzymes from various revertants display a wide spectrum of specific activity, thermolability and altered affinity for ligands such as P-enol pyruvate, ADP and fructose 1,6-diphosphate. The mutants produce materials crossreacting to the rabbit antibody raised against purified pyruvate kinase from the wild type yeast. These mutations thus define the structural gene of pyruvate kinase.The mutations map on the leaft arm of chromosome I and form a single complementation group with five other pyruvate kinase mutations in the pyk1 gene that was earlier suggested to be a regulatory locus controlling the synthesis of this enzyme. A comparative study of these mutants has been made with the structural mutants described here.     

Nitrogen metabolite repression in Aspergillus nidulans

Summary In Aspergillus nidulans, mutations, designated areA^r, can result in the inability to utilise a wide variety of nitrogen sources including amino acids, purines, amides, nitrate, and nitrite, whilst not affecting growth on ammonium. Other allelic areA mutations, designated areA^d, lead to derepression of one or more activities which are ammonium repressible in wild type (areA⁺) strains, whilst not affecting their inducibility. Various areA mutations exhibit a wide variety of phenotypes: areA^r alleles can be temperature sensitive on some nitrogen sources while not on others, and different alleles can be temperature sensitive for utilisation of different nitrogen sources. areA^d alleles can be derepressed for one ammonium-repressible activity, be normally repressible for another, and lead to abnormally low levels for a third. Once again each areA^d allele has its own highly specific phenotype. The inability of areA^r strains to utilise most nitrogen sources is paralleled by low activities of certain ammonium-repressible enzymes. areA^r mutations appear to be epistatic to some but not all regulatory mutations leading to constitutive synthesis of inducible enzymes and also epistatic to gdhA mutations which lead both to loss of NADP-linked glutamate dehydrogenase and to derepression of ammonium-repressible activities. areA^r mutations do not interfere with repair of a large number of auxotrophies in double mutants. Furthermore, although areA^r mutations prevent utilisation of L-arginine, L-ornithine, and L--amino-n-butyrate as nitrogen sources, they do not prevent the metabolism of these compounds necessary for repairing auxotrophies for proline and isoleucine in the appropriate double mutants. Utilisation of acetamide and most amino acids as carbon or carbon and nitrogen sources is unaffected by areA^r mutations, and areA^r strains are able to utilise acetamide and L-proline (but not other amino acids) as nitrogen sources in the presence of non-catabolite-repressing carbon sources such as L-arabinose, glycerol, melibiose, and lactose. Suppressor mutations, designated creA^d, probably leading to loss of carbon catabolite repression, allow utilisation of acetamide and proline as nitrogen sources in areA^r double mutants in the presence of carbon catabolite-repressing carbon sources. creA^d mutations allow ethanol to serve as a source of acetate for pyruvate dehydrogenaseless (pdhA) strains in the presence of carbon catabolite-repressing carbon sources, whereas pdhA single mutants respond to ethanol as sole carbon source only in the presence of non-carbon catabolite-repressing carbon sources. Specific suppressor mutations, designated amd ^d and prn ^d, allow utilisation of acetamide or proline, respectively, in areA^r double mutants.The areA locus can be interpreted as specifying a protein which is capable of (and in most cases essential for) allowing the synthesis of a number of enzymes of nitrogen metabolism but which cannot function in the presence of ammonium (i.e., as specifying a positive regulatory element which mediates ammonium repression) although the possibility that the areA product also plays a negative regulatory role cannot at present be ruled out.     

Riboflavin Overproduction in 4-Aminopyrazolo[3,4-d]pyrimidine-Resistant Mutants of Yeast Pichia guilliermondii

More than 90 mutants resistant to the adenine analogue 4-amino-pyrazolo[3,4-d]pyrimidine (4-APP), were isolated from a wild-type strain of yeast Pichia guilliermondii. Some of the App ^rmutants accumulated noticeable amounts of products absorbing at 260 nm in the culture medium, probably nucleotides and their derivatives. In comparison to the parent strain, the mutant App ^r-27 synthesized greater amounts of xanthine and uracil suggesting the presence of defects in the regulation of de novo biosynthesis of purines and pyrimidines. The regulatory mutations rib80 and rib81 are known to cause riboflavin (RF) overproduction and derepression of synthesis of corresponding enzymes in P. guilliermondii. The mutant App ^r-27 was crossed to the rib81 strain. The yield of RF biosynthesis in some meiotic segregants was significantly higher than that in segregants from the diploid rib81/RIB81. Apparently,rib81 and app ^r mutations were combined in a single genome on the favorable genetic background. An increase in RF production was also found in strains with app ^r mutations induced directly in the genome of the RF oversynthesizing strain rib80 rib81. These results indicate that introduction of app ^r mutations into the genome of P. guilliermondii can intensify their RF overproduction.     

Hyperproduction of dihydrofolate reductase in Diplococcus pneumoniae by mutation in the structural gene: The absence of an effect on other enzymes of folate coenzyme biosynthesis

A unique group of mutations (ame^r) in the dihydrofolate reductase (5,6,7,8-tetrahydrofolate:NADP⁺ oxidoreductase, EC 1.5.1.3.) structural gene of Diplococcus pneumoniae determine a marked overproduction of the corresponding enzyme protein. Since findings with these mutations relate to a key metabolic function and may be important to the regulation of folate coenzyme synthesis in general, the same group of multations were also examined for their effects on a number of related enzymic activities. Mutant and wild-type cell-free extracts, in addition to dihydrofolate reductase activity, exhibited both dihydropteroate and dihydrofolate synthetic activities under the conditions employed. Four folate coenzyme-related enzyme activities could also be demonstrated with the same preparations. These are mediated by the following enzymes, serine hydroxymethyl transferase (l-serine: tetrahydrofolate 10-hydroxymethyl tranferase, EC 2.1.2.1), 5, 10-methylenetetrahydrofolate dehydrogenase (5,10-methylenetetrahydrofolate: NADP⁺ oxidoreductase, EC 1.5.1.5), 10-formyltetrahydrofolate synthetase (formate: tetrahydrofolate ligase (ADP-forming), EC 6.3.4.3) and glutamate formiminotransferase (N-formimino-l-glutamate: tetrahydrofolate 5-formiminotransferase, EC 2.1.2.5). The ame^r mutations examined in the current study determined 3–80-fold increases in dihydrofolate reductase in comparison to the wild type. However, none of the other folate-related enzyme activities were altered. The possible significance of these findings in light of previous results is discussed.     

Carbohydrate metabolism during submerged production of ergot alkaloids

Summary The mycelial sugar composition and changes in specific activities of phosphofructokinase (PFK) and glucose-6-phosphate dehydrogenase, the key enzymes of the glycolytic and pentose-phosphate pathway of glucose catabolism, were followed throughout submerged fermentation of a high-yielding Claviceps purpurea L17 strain. Experimental data indicate that the pentose-phosphate pathway in glucose breakdown prevails during the vegetative phase of fermentation, the share of the glycolytic pathway becoming more pronounced during alkaloid synthesis. Both enzymes exhibit hyperbolic saturation kinetics, which is not usual for the PFK of eukaryotes. Offprint requests to: V. Gaberc-Porekar     

Tn916-induced mutants of Clostridium acetobutylicum defective in regulation of solvent formation

Sixteen Tn916-induced mutants of Clostridium acetobutylicum were selected that were defective in the production of acetone and butanol. Formation of ethanol, however, was only partially affected. The strains differed with respect to the degree of solvent formation ability and could be assigned to three different groups. Type I mutants (2 strains) were completely defective in acetone and butanol production and contained one or three copies of Tn916 in the chromosome. Analysis of the mutants for enzymes responsible for solvent production revealed the presence of a formerly unknown, specific acetaldehyde dehydrogenase. The data obtained also strongly indicate that the NADP⁺-dependent alcohol dehydrogenase is in vivo reponsible for ethanol formation, whereas the NAD⁺-dependent alcohol dehydrogenase is probably involved in butanol production. No activity of this enzyme together with all other enzymes in the acetone and butanol pathway could be found in type I strains. All tetracycline-resistant mutants obtained did no longer sporulate.Non-standard abbreviations AADC acetoacetate decarboxylase - AcaDH acetaldehyde dehydrogenase - BuaDH butyraldehyde dehydrogenase - CoA-TF acetoacetyl coenzyme A: acetate/butyrate: coenzyme A transferase - NAD-ADH, NAD⁺ dependent alcohol dehydrogenase - NADP-ADH, NADP⁺ dependent alcohol dehydrogenase     

THE BIOGENESIS OF MITOCHONDRIA IN SACCHAROMYCES CEREVISIAE : A Comparison between Cytoplasmic Respiratory-Deficient Mutant Yeast and Chloramphenicol-Inhibited Wild Type Cells

The effects of chloramphenicol on S. cerevisiae and on a cytoplasmic respiratory-deficient mutant derived from the same strain are compared. In the normal yeast, high concentrations of chloramphenicol in the growth medium completely inhibit the formation of cytochromes a, a₃, b, and c₁ and partially inhibit succinate dehydrogenase formation, whereas they do not affect cytochrome c synthesis. This has been correlated with the marked reduction of mitochondrial cristae formation in the presence of the drug. In glucose-repressed normal yeast, chloramphenicol has little effect on the formation of outer mitochondrial membrane, or on the synthesis of malate dehydrogenase and fumarase. However, both these enzymes, as well as the number of mitochondrial profiles, are markedly decreased when glucose de-repressed yeast is grown in the presence of chloramphenicol. The antibiotic did not appear to affect the cytoplasmic respiratory-deficient mutant. The results have been interpreted to indicate that chloramphenicol inhibits the protein-synthesizing system characteristic of the mitochondria. Since the drug does not prevent the formation of cytochrome c, of several readily solubilized mitochondrial enzymes, or of outer mitochondrial membrane, it is suggested that these are synthesized by nonmitochondrial systems.     

Comparative studies on the glycolytic and hexose monophosphate pathways in Candida parapsilosis and Saccharomyces cerevisiae

Some enzymatic activities of the glycolytic and hexose monophosphate pathways of Candida parapsilosis, a yeast lacking alcohol dehydrogenase but able to grow on high glucose concentrations, were compared to those of Saccharomyces cerevisiae. Cells were grown either on 8% glucose or on 2% glycerol and activities measured under optimal conditions. Results were as follows: glycolytic enzymes of C. parapsilosis, except glyceraldehyde 3-phosphate dehydrogenase, exhibited an activity weaker than that of S. cerevisiae, especially when yeasts were grown on glycerol. Fructose-1,6 bisphosphatase, an enzyme implicated in gluconeogenesis and in the hexose monophosphate pathway, and known to be very sensitive to catabolite repression in S. cerevisiae, was always active in C. parapsilosis even when cells were grown on 8% glucose. However, the allosteric properties towards AMP and fructose-2,6-bisphosphate were the same in both strains. Glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase, two other enzymes of the hexose monophosphate pathway, exhibited a higher activity in C. parapsilosis than in S. cerevisiae. Regulation of two important control points of the glycolytic flux, phosphofructokinase and pyruvate kinase, was investigated. In C. parapsilosis phosphofructokinase was poorly sensitive to ATP but fructose-2,60bisphosphate completely relieved the light ATP inhibition. Pyruvate kinase did not require fructose-1,6-bisphosphate for its activity, and by this way, did not regulate the glycolytic flux. The high glyceraldehyde-3-P-dehydrogenase activity, together with the relative insensitivity of fructose-1,6-bisphosphatase to catabolite repression and the high glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase activities suggested that in C. parapsilosis, as in other Candida species and opposite to S. cerevisiae, the glucose degradation mainly occurred through the hexose monophosphate pathway, under both growth conditions used.Abbreviations C. parapsilosis Candida parapsilosis - S. cerevisiae Saccharomyces cerevisiae - C. utilis Candida utilis     

Regulation of enzymes and isoenzymes of carbohydrate metabolism in the yeast Saccharomyces cerevisiae

An electrophoretic method has been devised to investigate the changes in the enzymes and isoenzymes of carbohydrate metabolism, upon adding glucose to derepressed yeast cells. (i) Of the glycolytic enzymes tested, enolase II, pyruvate kinase and pyruvate decarboxylase were markedly increased. This increase was accompanied by an overall increase in glycolytic activity and was prevented by cycloheximide, an inhibitor of protein synthesis. (ii) In contrast, respiratory activity decreased after adding glucose. This decrease was clearly shown to be the result of repression of respiratory enzymes. A rapid decrease within a few minutes of adding glucose, by analogy with the so-called ' Crabtree effect', was not observed in yeast. (iii) The gluconeogenic enzymes, fructose-1,6-bisphosphatase and malate dehydrogenase, which are inactivated after adding glucose, showed no significant changes in electrophoretic mobilities. Hence, there was no evidence of enzyme modifications, which were postulated as initiating degradation. However, it was possible to investigate cytoplasmic and mitochondrial malate dehydrogenase isoenzymes separately. Synthesis of the mitochondrial isoenzyme was repressed, whereas only cytoplasmic malate dehydrogenase was subject to glucose inactivation.     

Fructose-bisphosphatase-deficient mutants of the yeast Schizosaccharomyces pombe

We showed that in the yeast Schizosaccharomyces pombe, fructose-bisphosphatase is not subject to catabolite inactivation as it was observed in Saccharomyces cerevisiae. However, this enzyme activity is sensitive to catabolite repression in both yeasts. Two mutants lacking completely fructose-bisphosphatase activity were found. They were unable to grow on glycerol medium. They were still respiratory competent and exhibited the ability to derepress partially malate dehydrogenase activity. In glucose exponential phase culture, the parental strain lacks completely the fructosebisphosphatase activity due to catabolite repression. In these conditions, the growth is slowed down only in the mutants eventhough both mutants and their parental strain lack this enzyme activity. Normal sporulation and poor spore germination were observed for one mutant whereas, only in the presence of glucose, normal sporulation and normal spore germination were observed for the second mutant. Mendelian segregation of glycerol growth was found for the well germinating mutant. It is of nuclear heredity. The two mutations appeared to be closely linked.Abbreviations FBPase Fructose-1,6-bisphosphatase - fbp ^- genetic symbol for FBPase deficiency - glr ^- symbol for inability to grow on glycerol A. M. Colson is Research Associate au Fonds National de la Recherche Scientifique     

Enzymes related to galactose utilization inPseudomonas cepacia

Pseudomonas cepacia produced a characteristic green sheen on EMB-galactose plates owing to production of galactonic acid by the constitutive membrane-associated glucose dehydrogenase of this bacterium. Mutants isolated as glucose dehydrogenase deficient (Gcd^–) also were deficient in membrane-associated galactose dehydrogenase. A strain that formed glucose dehydrogenase at 30°C but not at 40°C was also temperature sensitive with respect to formation of galactose dehydrogenase. The Gcd^– strains still utilized galactose. A second, NAD-specific, galactose dehydrogenase (not membrane associated) along with a transport system for galactose were induced during growth on galactose and constituted an alternative pathway of conversion of galactose to galactonate. Enzymes of the De Ley-Doudoroff pathway of conversion of galactonate to pyruvate and glyceraldehyde-3-phosphate were induced during growth on galactose. Unexpectedly, growth on galactose also elicited formation of enzymes of the Entner-Doudoroff (ED) route. Furthermore, mutants blocked in the ED pathway grew poorly on galactose. One interpretation of these findings is that glyceraldehyde-3-phosphate formed from galactose via the De Ley-Doudoroff route (by cleavage of 2-keto-3-deoxy-6-phosphogalaconate) is reconverted to hexose phosphate and metabolized via the ED pathway.     

Regulation of enzymes and isoenzymes of carbohydrate metabolism in the yeast Saccharomyces cerevisiae

An electrophoretic method has been devised to investigate the changes in the enzymes and isoenzymes of carbohydrate metabolism, upon adding glucose to derepressed yeast cell. (i) Of the glycolytic enzymes tested, enolase II, pyruvate kinase and pyruvate decarboxylase were markedly increased. This increase was accompanied by an overall increase in glycolytic activity and was prevented by cycloheximide, an inhibitor of protein synthesis. (ii) In contrast, respiratory activity decreased after adding glucose. This decrease was clearly shown to be the result of repression of respiratory enzymes. A rapid decrease within a few minutes of adding glucose, by analogy with the so-called ‘Crabtree effect’, was not observed in yeast. (iii) The gluconeogenic enzymes, fructose-1,6-bisphosphatase and malate dehydrogenase, which are inactivated after adding glucose, showed no significant changes in electrophoretic mobilities. Hence, there was no evidence of enzyme modifications, which were postulated as initiating degradation. However, it was possible to investigate cytoplasmic and mitochondrial malate dehydrogenase isoenzymes separately. Synthesis of the mitochondrial isoenzyme was repressed, whereas only cytoplasmic malate hydrogenase was subject to glucose inactivation.     

A defect in carbon catabolite repression associated with uncontrollable and excessive maltose uptake

Summary The previously isolated recessive mutant allele hex2-3 of Saccharomyces cerevisiae caused a defect in carbon catabolite repression of maltase, invertase, malate dehydrogenase, and respiration but at the same time led to an extreme sensitivity to maltose (Zimmermann and Scheel, 1977; Entian and Zimmermann, 1980). Addition of maltose to a growing culture of a hex2-3 mutant resulted within 60 to 90 min in an inhibition of growth, glycolysis, and de novo protein synthesis. This was not accompanied by any abnormal levels of glycolysis metabolites or glycolytic enzyme activities. However, inhibitory effects coincided with a dramatic increase in intracellular glucose up to 150 mM relative to cell water as opposed to 2.5 mM in wild-type cells. This abnormal behavior is interpreted as a result of an uncontrolled maltose uptake in hex2 mutants, which in combination with increasing maltase activity results in an accumulation of intracellular glucose. Obviously the amount of available glucose surpassed glycolytic capacity in hex2 mutants.Properties of mutant alleles hex2 and hex1 (see Entian and Zimmermann, 1980) clearly show, that specific gene functions are involved in adapting the rate of sugar uptake into the cell to the actual glycolytic capacity.     

Synthesis of glycolytic and peroxisomal enzymes in Tetrahymena following a change in culture conditions

The specific activity of a peroxisomal enzyme, lactate oxidase, and of pyruvate kinase and lactate dehydrogenase, which are not peroxisomal, increased rapidly when shaken cultures of Tetrahymena were transferred to conditions of oxygen restriction and supplemented with glucose. Two other peroxisomal enzymes, catalase and TPN-linked isocitrate dehydrogenase, did not increase substantially, nor did succinate dehydrogenase. The increases were reduced if glucose was not added at the time of transfer, and were prevented by actinomycin D or cycloheximide, but not by chloramphenicol. The results suggest an involvement of peroxisomes in the metabolism of glycolytic endproducts when the availability of oxygen to the cell is limiting.     

Alterations in the energy metabolism of the isolated perfused frog heart during calcium depletion and subsequent repletion

Summary The changes in myocardial energy metabolism of isolated perfused Rana ridibunda hearts subjected to prolonged calcium depletion and reperfusion with calcium-containing medium were studied. Calcium-free perfusion resulted in an increase in the concentrations of glucose, glucose-6-phosphate, a-ketoglutarate and malate. The myocardial contents of high-energy phosphates were maintained while concentrations of key amino acids were significantly altered. During the reperfusion period the tissue high-energy phosphate content fell abruptly. A marked increase in glycolytic flux and lactate production was observed. The tissue contents of citric acid cycle intermediates and key amino acids decreased. Examination of the activities of marker enzymes during the calcium-free and reperfusion periods showed that only cytoplasmic enzymes are lost during reperfusion, while the activities of other enzymes remained unchanged. The results suggest that the fluxes of both glycolysis and the citric acid cycle are significantly altered during calcium depletion and following repletion in the amphibian heart. The major characteristics of calcium paradox-induced damage in Rana ridibunda heart are the depletion of high-energy stores, the impairment of mitochondrial oxidative metabolism, and a significant increase in anaerobic metabolism.Abbreviations ADP Adenosine diphosphate - AMP Adenosine monophosphate - ATP Adenosine triphosphate - EDTA Ethylene-diamino-tetraacetic acid - NAD ⁺ Nicotinamide-adeninedinucleotide - NADH Nicotinamide-adenine-dinucleotide (reduced form) - TRA Triethanolamine     

Hexose phosphate metabolism and exopolysaccharide formation inPseudomonas cepacia

When grown on solid medium containing excess glucose, glucose dehydrogenase-deficient (Gcd^–) mutants ofPseudomonas cepacia 249 formed large amounts of an exopolysaccharide comprised of galactose, glucose, mannose, glucuronic acid, and rhamnose. The Gcd⁺ parent strain failed to accumulate comparable amounts of exopolymer from glucose because of its rapid conversion of glucose to gluconic and 2-ketogluconic acids and its lower content of enzymes related to glucose-1-phosphate synthesis. Both Gcd⁺ and Gcd^– strains ofP. cepacia accumulated exopolymer when substrates such as mannitol and glycerol were substituted for glucose. A survey of clinical isolates from patients with cystic fibrosis indicated that there was no correlation between ability ofP. cepacia to colonize the respiratory tracts of such individuals and increased capacity to form exopolymer related to glucose dehydrogenase deficiency.     

Pleiotropic mutants of Aspergillus nidulans altered in carbon metabolism.

Summary Mutants altered in carbon catabolite regulation have been isolated by selecting for mutants of theareA217 strain capable of using acetamide as the sole nitrogen source in the presence of sucrose. In addition tocreA mutants described previously by Arst and Cove, strains with mutations in two new genes,creB andcreC, have been found. ThecreB andcreC mutants grow poorly on some sole carbon sources and have low levels of some enzymes of carbon catabolism e.g. -galactosidase and D-quinate dehydrogenase. ThecreB andcreC mutants are hypersitive to fluoroacetate, fluoroacetamide and allyl alcohol in the presence of glucose or sucrose but not glycerol; and the enzymes, acetamidase, and alcohol dehydrogenase, are less sensitive to carbon catabolite repression than the wild-type strain. Extracellular protease and -glucosidase enzyme activities are elevated increB andcreC mutants, while L-proline and L-glutamate uptake capacities are lower in both the presence and absence of glucose. Interactions betweencreA, B and C mutations have been investigated in double mutants, and the dominance properties ofcreB andcreC mutants determined. The results indicate that thecreB andcreC genes may have a regulatory role in the control of carbon catabolism.