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  • 1
    Electronic Resource
    Electronic Resource
    Dilution rate as a determinant of mycelial morphology in continuous culture (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 38 (1991), S. 75-81 
    Details
    ISSN: 0006-3592
    Keywords: mycelial morphology ; Fusarium graminearum ; mycoprtein ; continuous culture ; chemostat ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The morphology of mycelial fungi in liquid culture effects culture rheology and this in turn may affect product yield. It is therefore important to understand how environmental factors influence mycelial morphology and this paper describes the effect of dilution rate on two strains of Fusarium graminearum, the relatively sparsely branched parental strain (A3/5) and a relatively highly branched “colonial” variant (C106). At any given dilution rate, the concentration of mycelial fragments present at steady state of both strains remained approximately constant with time, suggesting that mycelial fragmentation occurred in a regular manner. However, for both strains fragment concentration decreased with increasing dilution rate. The strains had a similar morphology at a dilution rate of 0.07 h-1. The length of the hyphal growth unit of A3/5 increased with increase in dilution rate, while that of C106 decreased with increase in dilution rate. At all dilution rates, C106 produced up to ten times more macroconidia than A3/5.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260380110
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  • 2
    Electronic Resource
    Electronic Resource
    Nutrient-dependent selection of morphological mutants of Fusarium graminearum A3/5 isolated from long-term continuous flow cultures (1992)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 40 (1992), S. 1181-1189 
    Details
    ISSN: 0006-3592
    Keywords: Fusarium graminearum ; continuous culture ; chemostat ; morphological mutants ; selection coefficient ; Ks value ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Highly branched (colonial) mutants (MC1-1-, CC1-1, and C106) of Fusarium graminearum A3/5 were each grown with the parental strain (A3/5) in continuous flow cultures at high and low dilution rates using a variety of nutrient limitations. MC1-1 replaced A3/5 in all nutrient-limited cultures tested (glucose-, Mg2+-, ammonium-, and sulphate-limited cultures), suggesting that it has a higher maximum specific growh rate than A3/5. Compared with A3/5, C106 was positively selected for in Mg2+-limited cultures and its selection coefficient was higher at low than at high dilution rates, suggesting that, compared with A3/5, it has a reduced saturation constant (Ks) for Mg2+. However, in batch culture, C106 and A3/5 had the same (15 μM) appaent Ks value for Mg2+. C106 was replaced (negative selection coefficient) by A3/5 in gluose-, ammonium-, and phsophate-limited continuous flow cultures, but was neither at an advantage nor a disadvantage (i.e., it behaved as a neutral mutation) in sulphate-limited cultures. CC1-1 replaced A3/5 when they were grown together in glucose-, maltose-, or ribose-limited continuous flow cultures, but not in fructose-, xylose-, ammonium-, or phsophate-limited cultures. Because A3/5 and CC1-1 had similar Km values (30 μM) for glucose, and because the selective advantage of CC1-1 was maintained in maltose-limited cultures (maltose was not hydrolyzed extracellularly), it was concluded that the selective advantage of CC1-1 did not result from it having a lower Ks for glucose than the parental strain. Rather, the data suggested that the activity of phosphoketopentoepimerase may be altered by the CC1-1 mutation. © 1992 John Wiley & Sons, Inc.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260401007
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  • 3
    Electronic Resource
    Electronic Resource
    pH oscillations and constant low pH delay the appearance of highly branched (colonial) mutants in chemostat cultures of the quorn® myco-protein fungus, Fusarium graminearum A3/5 (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 51 (1996), S. 61-68 
    Details
    ISSN: 0006-3592
    Keywords: chemostat culture ; mutants, colonial ; Fusarium graminearum A3/5 ; periodic selection ; mycoprotein ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: At pH 5.8, highly branched (colonial) mutants appear in glucose-limited chemostat cultures of Fusarium graminearum A3/5 after ca. 400 h (ca. 107 generations) of growth. The appearance of these mutants was delayed by up to 144 h (45 generations) when the culture was switched at intervals of 120 h between pH 4.8 and 6.6. The concentration of cycloheximide-resistant macroconidia in the culture was used as an indicator of the periodic selection of advantageous mutants and it was found that, in chemostat populations subjected to pH oscillations, the interval (210 ± 20 h) between peaks was nearly double that observed in chemostat populations cultured at constant pH (124 ± 12 h at constant pH 5.8 and 120 h ± 17 h at constant pH 4.5), indicating that the population evolved more slowly under oscillating pH than under constant pH. When grown in mixed culture with the parental strain (A3/5), the selective advantage of two colonial mutants isolated from chemostat cultures grown under conditions of oscillating pH was found to be pH dependent. Compared to cultures grown at constant pH 5.8, a delay of ca. 312 h (87 generations) in the appearance of colonial mutants was observed when F. graminearum A3/5 was grown in glucose-limited chemostat culture at constant pH 4.5. © 1996 John Wiley & Sons, Inc.
    Additional Material: 3 Ill.
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  • 4
    Electronic Resource
    Electronic Resource
    Optimization and stability of glucoamylase production by recombinant strains of Aspergillus niger in chemostat culture (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 59 (1998), S. 407-418 
    Details
    ISSN: 0006-3592
    Keywords: Aspergillus niger ; chemostat culture ; glucoamylase (GAM) ; protein secretion ; recombinant protein ; strain stability ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: When grown on a medium containing 5 g maltodextrin L-1, Aspergillus niger transformant N402[pAB6-10]B1, which has an additional 20 copies of the glucoamylase (glaA) gene, produced 320 ± 8 mg (mean ± S.E.) glucoamylase (GAM) L-1 in batch culture and 373 ± 9 mg GAM L-1 in maltodextrin-limited chemostat culture at a dilution rate of 0.13 h-1. These values correspond to specific production rates (qp) of 5.6 and 16.0 mg GAM [g biomass]-1 h-1, respectively. In maltodextrin-limited chemostat cultures grown at dilution rates from 0.06 to 0.14 h-1, GAM was produced by B1 in a growth-correlated manner, demonstrating that a continuous flow culture system operated at a high dilution rate is an efficient way of producing this enzyme. In chemostat cultures grown at high dilution rates, GAM production in chemostat cultures was repressed when the limiting nutrient was fructose or xylose, but derepressed when the limiting nutrient was glucose (qp, 12.0), potassium (6.2), ammonium (4.1), phosphate (2.0), magnesium (1.5) or sulphate (0.9). For chemostat cultures grown at a dilution rate of 0.13 h-1, the addition of 5 g mycopeptone L-1 to a glucose-mineral salts medium resulted in a 64% increase in GAM concentration (from 303 ± 12 to 496 ± 10 mg GAM L-1) and a 37% increase in specific production rate (from 12.0 ± 0.4 to 16.4 ± 1.6 mg GAM [g biomass]-1 h-1). However, although recombinant protein production was stable for at least 948 h (191 generations) when A. niger B1 was grown in chemostat culture on glucose-mineral salts medium, it was stable for less than 136 h (27 generations) on medium containing mycopeptone. The predominant morphological mutants occurring after prolonged chemostat culture were shown to have selective advantage in the chemostat over the parental strain. Compared to their parental strains, two morphological mutants had similar GAM production levels, while a third had a reduced production level. Growth tests and molecular analysis revealed that the number of glaA gene copies in this latter strain (B1-M) was reduced, which could explain its reduced GAM production. Shake-flask cultures carried out with the various morphological mutants revealed that in batch culture all three strains produced considerably less GAM than their parent strains and even less than N402. We show that physiological changes in these morphological mutants contribute to this decreased level of GAM production. © 1998 John Wiley & Sons, Inc. Biotechnol Bioeng 59:407-418, 1998.
    Additional Material: 6 Ill.
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