Enhanced enzyme production with the pelleted form of <Emphasis Type="Italic">D. squalens</Emphasis> in laboratory bioreactors using added natural lignin inducer |
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Authors: | Janja Babi? Aleksander Pavko |
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Institution: | (1) Faculty of Chemistry and Chemical Technology, University of Ljubljana, Aškerčeva 5, 1000 Ljubljana, Slovenia; |
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Abstract: | White-rot fungi are extensively used in various submerged biotechnology processes to produce ligninolytic enzymes. Transfer
of the process from the laboratory to the industrial level requires optimization of the cultivation conditions on the laboratory
scale. An interesting area of optimization is pellet growth since this morphological form solves problems such as the decreased
oxygen concentration, limited heat, and nutrient transport, which usually occur in dispersed mycelium cultures. Many submerged
fermentations with basidiomycetes in pellet form were done with Phanerochaete, Trametes, and Bjerkandera species, among others. In our study, another promising basidiomycete, D. squalens, was used for ligninolytic enzyme production. With the addition of wood particles (sawdust) as a natural inducer and optimization
of mixing and aeration conditions in laboratory stirred tank (STR) and bubble column (BCR) reactors on pellet growth and morphology,
the secretion of laccase and the manganese-dependent peroxidase into the medium was substantially enhanced. The maximum mean
pellet radius was achieved after 10 days in the BCR (5.1 mm) where pellets were fluffy and 5 days in the STR (3.5 mm) where
they were round and smooth. The maximum Lac activity (1,882 U l−1) was obtained after 12 days in the STR, while maximum MnP activity (449.8 U l−1) occurred after 18 days in the BCR. The pellet size and morphology depended on the agitation and aeration conditions and
consequently influenced a particular enzyme synthesis. The enzyme activities were high and comparable with the activities
found for other investigations in reactors with basidiomycetes in the form of pellets. |
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