Isolation of mutants of Alcaligenes eutrophus unable to derepress the fermentative alcohol dehydrogenase |
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Authors: | A Steinbüchel C Fründ D Jendrossek H G Schlegel |
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Institution: | (1) Institut für Mikrobiologie der Universität Göttingen, Grisebachstrasse 8, D-3400 Göttingen, Federal Republic of Germany |
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Abstract: | Eight representative strains of Alcaligenes eutrophus, two strains of Alcaligenes hydrogenophilus and three strains of Paracoccus denitrificans were examined for their ability to use different alcohols and acetoin as a carbon source for growth. A. eutrophus strains N9A, H16 and derivative strains were unable to grow on ethanol or on 2,3-butanediol. Alcohol-utilizing mutants derived from these strains, isolated in this study, can be categorized into two major groups: Type I-mutants represented by strain AS1 occurred even spontaneously and were able to grow on 2,3-butanediol (t
d=2.7–6.4 h) and on ethanol (t
d=15–50 h). The fermentative alcohol dehydrogenase was present on all substrates tested, indicating that this enzyme in vivo is able to oxidize 2,3-butanediol to acetoin which is a good substrate for wild type strains. Type II-mutants represented by strain AS4 utilize ethanol as a carbon source for growth (t
d=3–9 h) but do not grow on butanediol. In these mutants the fermentative alcohol dehydrogenase is only present in cells cultivated under conditions of restricted oxygen supply, but a different NAD-dependent alcohol dehydrogenase is present in ethanol grown cells. Cells grown on ethanol, acetoin or 2,3-butanediol synthesized in addition two proteins exhibiting NAD-dependent acetaldehyde dehydrogenase activity and acetate thiokinase. An acylating acetaldehyde dehydrogenase (EC 1.2.1.10) was not detectable. Applying the colistin- and pin point-technique for mutant selection to strain AS1, mutants, which lack the fermentative alcohol dehydrogenase even if cultivated under conditions of restricted oxygen supply, were isolated; the growth pattern served as a readily identifiable phenotypic marker for the presence or absence of this enzyme. |
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Keywords: | Alcaligenes eutrophus Butanediol cycle Acetaldehyde dehydrogenase Acetate thiokinase Butanediol dehydrogenase Acetoin metabolism Alcohol dehydrogenase Constitutive mutants |
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