METABOLIC CONTROL OF β-GLUCOSIDASE SYNTHESIS IN YEAST

BETA-GLUCOSIDASE SYSTEM OF NEUROSPORA CRASSA. I. BETA-GLUCOSIDASE AND CELLULASE ACTIVITIES OF MUTANT AND WILD-TYPE STRAINS

Eberhart, Bruce (University of North Carolina, Greensboro), David F. Cross, and Lewis R. Chase. beta-Glucosidase system of Neuspora crassa. I. beta-Glucosidase and cellulose activities of mutant and wild-type strains. J. Bacteriol. 87:761-770. 1964.-A mutant strain, gluc-1, of Neurospora crassa was isolated and characterized by its low level of beta-glucosidase activity. The mutant was selected by testing irradiated colonies for extracellular beta-glucosidase activity. Strains containing the gluc-1 gene were also visibly detected by their reduced ability to destroy esculin in their growth media. The mutant strain grew at wild-type rates with cellobiose or carboxymethylcellulose as carbon sources. This auxotrophic similarity with wild type is explained by the presence of at least two beta-glucosidases (and possibly two cellulases) in Neurospora that act complementarily. The thermolabile beta-glucosidase was destroyed after 1 min of incubation at 60 C. This enzyme was present in mycelia but absent in conidial extracts. A second beta-glucosidase that is comparatively stable at 60 C was present in both mycelia and conidia. A partial separation of these enzymes was achieved with ammonium fractionation of mycelial extracts of gluc-1 and wild-type strains. Thermolabile beta-glucosidase and cellulase activity appear not to be affected by the gluc-1 mutation, whereas the thermostable glucosidase is greatly reduced in gluc-1 strains.

METABOLIC REGULATION OF ADENOSINE TRIPHOSPHATE SULFURYLASE IN YEAST

de Vito, Peter C. (Princeton University, Princeton, N.J.), and Jacques Dreyfuss. Metabolic regulation of adenosine triphosphate sulfurylase in yeast. J. Bacteriol. 88:1341-1348. 1964.-The metabolic regulation of adenosine triphosphate sulfurylase (ATP-sulfurylase) from baker's yeast was studied. The enzyme was strongly inhibited by low concentrations of adenosine-5'-phosphosulfate, 3'-phosphoadenosine-5'-phosphosulfate, and sulfide. Sulfide ion was a competitive inhibitor of ATP-sulfurylase. Cysteine, methionine, sulfite, and thiosulfate were not inhibitors of the enzyme. ATP-sulfurylase was repressed when yeast was grown in the presence of methionine, and derepressed when yeast was grown in the presence of cysteine. In contrast to these results, the enzyme sulfite reductase was repressed in cysteine-grown cells. Thus, the sulfate-reducing pathway in yeast appears to be regulated at its first step both by feedback inhibition (by sulfide) and by repression (by methionine). Other known controls in the cysteine biosynthetic pathway are discussed.

Production of beta-glucosidase and diauxic usage of sugar mixtures by Candida molischiana

The fermentation of cellobiose is a rare trait among yeasts. Of the 308 yeast species that utilize cellobiose aerobically, only 12 species ferment it, and only 2 species, Candida molischiana and Candida wickerhamii, also ferment cellodextrins. Candida molischiana produced beta-glucosidase activity on all carbon sources tested, except glucose, mannose, and fructose. When these sugars were added to cultures growing on cellobiose, the synthesis of beta-glucosidase ceased. However, the total amount of enzyme activity remained constant, indicating that the C. molischiana beta-glucosidase is catabolite repressed and not catabolite inactivated. When grown in medium initially containing glucose plus xylose, cellobiose, maltose, mannitol, or glucitol, C. molischiana preferentially utilized glucose and produced little beta-glucosidase activity until glucose was nearly depleted from the medium. When grown in medium containing cellobiose plus either fructose or mannose, the yeast preferentially utilized the monosaccharides and produced little beta-glucosidase activity. Candida molischiana produced beta-glucosidase and co-utilized cellobiose and xylose, maltose, or trehalose. Glucose and fructose, mannose, or trehalose were co-utilized; however, no beta-glucosidase activity was detected. Thus, the order of substrate preference groups appeared to be (glucose, trehalose, fructose, mannose) > (cellobiose, maltose, xylose) > (mannitol, glucitol).

Utilization of glucose and cellobiose byCandida molischiana

Some of the factors that influence the biosynthesis of the Candida molischiana β-glucosidase were investigated. The yeast produced maximal enzyme activity when grown at 28 °C in a carbohydrate-containing complex medium (YM) in which the initial pH was adjusted to 6.0. The enzyme appeared to be produced constitutively, as activity was detected when either ethanol, glycerol, xylose, glucitol, mannitol, maltose, trehalose, cellobiose, cellodextrins, or soluble starch was used as the carbohydrate source. The presence of either glucose, mannose, or fructose (> 25 g/L) repressed β-glucosidase expression; however, C. molischiana did produce β-glucosidase when the initial glucose concentration was <25 g/L. When the yeast was grown in YM medium containing glucose plus cellobiose, diauxic utilization of the carbon sources was observed, and β-glucosidase activity was not detected until the glucose was depleted from the medium.Key words: β-glucosidase, glucose repression, fermentation, yeast.

Regulation of β-1, 4-Glucosidase Expression by Candida wickerhamii

Candida wickerhamii NRRL Y-2563 expressed β-glucosidase activity (3 to 8 U/ml) constitutively when grown aerobically in complex medium containing either glycerol, succinate, xylose, galactose, or cellobiose as the carbon source. The addition of a high concentration of glucose (>75 g/liter) repressed β-glucosidase expression (<0.3 U/ml); however, this yeast did produce β-glucosidase when the initial glucose concentration was ≤50 g/liter. When grown aerobically in medium containing glucose plus the above-listed carbon sources, diauxic utilization of the carbon source was observed and the expression of β-glucosidase was glucose repressed. Surprisingly, glucose repression did not occur when the cells were grown anaerobically. When grown anaerobically in medium containing 100 g of glucose per liter, C. wickerhamii produced 6 to 9 U of enzyme per ml and did not demonstrate diauxic utilization of glucose-cellobiose mixtures. To our knowledge, this is the first report of apparent derepression of a glucose-repressed enzyme by anaerobiosis.

Cloning and expression of the structural gene for beta-glucosidase of Kluyveromyces fragilis in Escherichia coli and Saccharomyces cerevisiae

Cellobiose, the last product in cellulose degradation, is converted into two molecules of glucose by a beta-glucosidase. S. cerevisiae does posses the structural gene for a beta-glucosidase, but it is very poorly expressed; we thus decided to isolate and characterize that of Kluyveromyces fragilis. We constructed in E. coli HB101 strain a genomic library of the Kluyveromyces fragilis Y610 strain (ATCC 12424), a yeast able to grow on cellobiose and which constitutively produces the beta-glucosidase. The structural gene for beta-glucosidase was identified by its expression in E. coli. The initial isolated cosmid KF1 contained an insert of 35 Kb and by successive subcloning the insert size was reduced to 3.5 Kb (KF4). This cloned beta-glucosidase gene introduced in S. cerevisiae by transformation is expressed at a level of about 500 times that of K. fragilis. We checked by Southern hybridization that the high expression level was not due to a rearrangement of K. fragilis DNA during the cloning experiments. Nevertheless to obtain yeast transformants able to grow on cellobiose a yeast strain whose permeability to sugar is increased must be used and this last point is discussed.

Utilization of glucose and celloboise by the microflora of soil enriched with cellulose

The ability of soil microflora to utilize glucose or celloboise was found to depend on previous incubation of the soil with glucose, celloboise or cellulose. Glucose was utilized more rapidly than cellobiose in soil preincubated with glucose or cellobiose. The opposite situation was observed in soil preincubated with cellulose. In the presence of a mixture of both sugars the rate of utilization of one of them was decreased by the second and this decrease could be characterized as competitive inhibition. Glucose accumulated in the medium during utilization of cellobiose alone in soil preincubated with cellulose. This phenomenon was not observed during the utilization of cellobiose in soil preincubated with glucose or cellobiose.

Induction and catabolite repression of L-rhamnose dehydrogenase in Pullularia pullulans

The growth of Pullularia pullulans on L-rhamnose (6-deoxy-L-mannose) as the sole carbon source induces the synthesis of L-rhamnose dehydrogenase, a nicotinamide adenine dinucleotide-dependent enzyme that catalyzes the oxidation of the deoxy sugar to L-rhamnonolactone. The enzyme induction is inhibited by cycloheximide, suggesting de novo synthesis. The presence of d-glucose (0.2%) or D-galactose (0.2%) simultaneously with the inducer in the induction medium produced 50% repression of dehydrogenase synthesis, but no effect was detected with D-fructose and D-mannose at the same concentration. High levels of D-glucose (2%), under maximal catabolite repression conditions, produced a complete inhibition of enzyme synthesis.

Biochemical and genetic characterization of -glucosidase mutants in Saccharomyces lactis

Mutants with reduced activity for beta-glucosidase (beta-d-glucoside glucohydrolase EC 3.2.1.21) were isolated from the haploid yeast Saccharomyces lactis. Tetrad analysis indicated that in each mutant a single genetic factor, closely linked or allelic to the structural gene for beta-glucosidase (B locus), is responsible for the decreased activity. beta-Glucosidases produced by wild-type and mutant strains are similar in molecular size and charge but differ in catalytic properties, thermal stability, and serological specificity, indicating that mutants are in the structural gene. All mutants retained their capacity to be induced by either methyl-beta-d-glucoside or glucose. In all cases, the mutant phenotype was dominant in heterozygous diploids.

Mutants in Saccharomyces lactis controlling both -glucosidase and -galactosidase activities

InSaccharomyces lactis, a class of mutants isolated for low β-glucosidase activity are reduced in activity for β-galactosidase as well. Genetic studies indicate that their properties are the result of a single mutation in a nuclear gene. In diploide containing a wild-type and mutant β-galactosidase allele, the mutant phenotype is partially dominant. The two enzymes can be separated physically and under appropriate conditions are induced independently in wild-type strains.

Synthesis of Protocatechuate Oxygenase by Pseudomonas fluorescens in the Presence of Exogenous Carbon Sources

Kirkland, Jerry J. (Oklahoma State University, Stillwater), and Norman N. Durham . Synthesis of protocatechuate oxygenase by Pseudomonas fluorescens in the presence of exogenous carbon sources. J. Bacteriol. 90: 15–22. 1965.—The addition of glucose, ribose, or fructose (0.45 or 45.0 μmoles/ml) simultaneously with protocatechuic acid shortens the lag period required for synthesis of protocatechuate oxygenase by a washed-cell suspension of Pseudomonas fluorescens . Glucose is readily oxidized and supports growth of P. fluorescens , whereas neither ribose nor fructose readily supports growth. High glucose concentrations (45.0 μmoles/ml) shorten the lag period but lower the total enzyme synthesis. The p H drops during glucose oxidation, and this is accompanied by a decrease in the rate of enzyme synthesis. High glucose concentrations, with adequate buffering, permitted “normal” enzyme synthesis. A decrease in the total enzyme synthesis was not observed in the presence of high concentrations of ribose or fructose. Succinate, pyruvate, acetate, or formate (0.45 μmole/ml) were readily oxidized, but did not shorten the lag period required for synthesis of the enzyme. The data suggest that glucose, ribose, or fructose may serve as a “specific” carbon source (such as ribose-5-phosphate or a similar precursor important in ribonucleic acid synthesis) functional in the synthesis of protocatechuate oxygenase.

β-Glucosidase Activity in Phytopathogenic Bacteria

Most of 58 isolates of phytopathogenic and related bacteria comprising 24 species in the genera Agrobacterium, Erwinia, Corynebacterium, Pseudomonas , and Xanthomonas exhibited β-glucosidase activity, especially the gall-nonforming pathogenic pseudomonads and soft rot organisms. The gall-forming pseudomonads and P. fluorescens exhibited no β-glucosidase activity, with the exception of one isolate of P. savastanoi which showed slight activity on an inorganic nitrogen-arbutin medium. The best medium for demonstrating β-glucosidase activity contained peptone as the nitrogen source and arbutin. β-Glucosidase activity in this medium was indicated by either acid production or browning. P. syringae , in contrast to other bacteria tested, produced most β-glucosidase in a medium containing large amounts of glucose. Chromatographic analyses confirmed that splitting of the glucoside occurred at the glucosidic linkage. Reaction of sonically treated bacterial cells with indican or p -nitrophenyl-β-D-glucoside proved a rapid method for assaying relative amounts of β-glucosidase among bacterial species. Harda's paper-strip method of detecting β-glucosidase also was useful in revealing the distribution and relative amounts of β-glucosidase in most bacteria, but did not indicate the relatively greater amount of β-glucosidase in P. syringae .

METABOLIC CONTROL OF PENICILLINASE BIOSYNTHESIS IN BACILLUS CEREUS

Yip, Lily C. (University of Cincinnati, Cincinnati, Ohio), Ramesh Shah, and Richard A. Day . Metabolic control of penicillinase biosynthesis in Bacillus cereus . J. Bacteriol. 88: 297–308. 1964.—Penicillinase production in strains 5 and 5/B of Bacillus cereus in response to treatment by 6-aminopenicillanic acid (APA), penicillin G, (6- N -α-( p -benzyloxyphenoxy)-propionylamino-penicillanic acid, and cephalosporin C (CC) was found to be analogous to that seen in constitutive strains. Strain 5 did not release penicillinase into the medium to any great extent. Penicillinase production and the effect of the above penicillins on it were found to decline with increasing density of the culture. The penicillins were shown to accelerate or retard the production of penicillinase activity in strain 5 cells during pretreatment at 0 C and during incubation at 37 C. Strains 5 and 5/B gave qualitatively similar responses to penicillin treatment. At 0 C, the specific activity of penicillinase in strain 5 passes through a period of rapid increase at 0 hr and a period of little change at approximately 1 hr, followed by an increased rate of change towards 2 hr. The effect of APA or CC on specific activity of strain 5 cells during treatment at 0 C could not be reversed by one another, but Hg could reverse the increase caused by CC to some extent and the repression caused by APA. The production of penicillinase in the microconstitutive strain 5 of Bacillus cereus in response to treatment with CC was influenced by various inhibitors. 8-Azaguanine inhibited the production of the enzyme both during a pretreatment of the cells with CC at 0 C and during the subsequent incubation at 37 C. Actinomycin D, 6-azauracil, 6-thioguanine, and 2-thiocytosine inhibit the increase in penicillinase arising after the pretreatment at 0 C. 6-Azathymine has very little effect on the change of penicillinase activity. The CC-induced change occurring during the 0 C period was postulated to be a process at the level of protein biosynthesis itself; change at 37 C, constituting a delayed response, was considered a process at the level of messenger ribonucleic acid synthesis.

CONTROL OF ISOCITRATASE FORMATION IN RHIZOPUS NIGRICANS

Wegener, Warner S. (University of Cincinnati, Cincinnati, Ohio), and Antonio H. Romano . Control of isocitratase formation in Rhizopus nigricans . J. Bacteriol. 87: 156–161. 1964.—A fumaric acid-producing strain of Rhizopus nigricans was found to produce a fair level of isocitratase in a casein hydrolysate medium. Glucose repressed enzyme formation. When glucose was utilized during growth, there was a relief of repression, and enzyme synthesis was resumed at a rate equivalent to that found in nonrepressed cells. Zinc stimulated isocitratase formation in glucose-repressed cultures by stimulating growth and glucose utilization, thereby decreasing accumulation of repressor metabolites derived from glucose. The effectiveness of acetate as an inducer was greater on glucose-repressed cells than on nonrepressed cells; cells grown in the presence of glucose formed higher levels of isocitratase when subsequently replaced with an acetate-containing inductive medium than did cells grown without glucose. Moreover, addition of 2 ppm of Zn ++ during the inductive replacement phase resulted in a twofold increase in isocitratase formation. The hypothesis is submitted that Zn ++ exerts its action by stimulating ribonucleic acid (RNA) synthesis, thereby facilitating the formation of a specific RNA during induction. Preliminary evidence implicating Zn ++ in the stimulation of RNA synthesis in this organism is presented.

GENETIC CONTROL OF β-GLUCOSIDASE SYNTHESIS IN SACCHAROMYCES LACTIS

Herman, Alberta (University of Wisconsin, Madison) and Harlyn Halvorson . Genetic control of β-glucosidase synthesis in Saccharomyces lactis . J. Bacteriol. 85: 901–910. 1963.—Both methyl-β- d -glucoside (2 × 10 −2 m ) and glucose (10 −3 m ) induced β-glucosidase synthesis in selected strains of Saccharomyces lactis . Genetic studies indicated the existence of a single locus specifically affecting β-methyl glucoside inducibility. Glucose-induced β-glucosidase synthesis, on the other hand, was nonspecific (other carbohydrases were simultaneously induced) and appeared to be controlled by more than one genetic factor. In both cases, noninducibility was dominant in diploids. The independent expression of these two modes of induction implied that these loci regulated β-glucosidase induction in a nonsequential manner.

IDENTIFICATION OF THE STRUCTURAL GENE FOR β-GLUCOSIDASE IN SACCHAROMYCES LACTIS

Herman, Alberta (University of Wisconsin, Madison) and Harlyn Halvorson . Identification of the structural gene for β-glucosidase in Saccharomyces lactis . J. Bacteriol. 85: 895–900. 1963.—Three allelic forms (B h, m, l ) of the structural gene for β-glucosidase have been identified in the yeast Saccharomyces lactis . Evidence that these are structural gene alleles includes the independent expression of the alleles in homozygous and heterozygous diploids and differences in the specificity and in the physical properties of the enzyme produced in response to the various allelic mutations. Two factors, one controlling production of the pulcherrimin-like pigment, the other β-galactosidase activity, are linked to the B locus. The β-glucosidase in these strains hydrolyzes the chromogenic substrate, p -nitrophenyl-β- d -glucoside, arbutin, salicin, and esculin. Cellobiose, on the other hand, is hydrolyzed by another enzyme.

PHYSIOLOGICAL CHANGES OCCURRING IN YEAST UNDERGOING GLUCOSE REPRESSION

MacQuillan, Anthony M. (The University of Wisconsin, Madison) and Harlyn O. Halvorson . Physiological changes occuring in yeast undergoing glucose repression. J. Bacteriol. 84: 31–36. 1962.—Growth of the hybrid yeast Saccharomyces fragilis × S. dobzhanskii on glucose or lactate resulted in (i) the possible impairment of a permeation system for succinic acid, (ii) the repression of succinic and isocitric dehydrogenases and β-glucosidase, and (iii) the induction of isocitratase. The latter two changes were not observed in S. lactis Y14, in which β-glucosidase synthesis is resistant to glucose repression.