Browsing by Subject "mikrobiologia, Biotekniikka"

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  • Mattila, Hans (Helsingin yliopisto, 2020)
    White rot Basidiomycota can decompose all wood components in nature and are therefore essential in recycling carbon in our forests and ecosystems. These fungi are filamentous organisms that reside on top of trunks and elongate their hyphae inside wood particles which may be waterlogged or submerged by vegetation and debris. Therefore, it is likely these organisms are occasionally subjected to limited oxygen availability. This doctoral thesis elucidated how this atmospheric shift steers the metabolism of a white rot fungus and how this phenomenon can be used in bioethanol production. This thesis explored a group of white rot fungi for their capability to produce ethanol from wood and lignocellulose containing waste material. One isolate, Phlebia radiata 79 (FBCC0043) turned out to be efficient in producing ethanol from waste substrates in considerable quantities. This isolate was used to develop a single-step single-organism bioethanol production method. A wide range of substrates e.g. saw dust, straw, board and recycled wood waste were used as substrates for ethanol production. Up to 32 g/L of ethanol was obtained from solid-state cultivations with core board. Fungal wood decomposition is considered strictly aerobic; however, Phlebia radiata could convert lignocellulose into ethanol under fermentative and oxygen depleted conditions. Therefore, gene expression of P. radiata was studied after 14 days of cultivation under oxygen depletion or hypoxia. The research concentrated on the expression of both the extracellular carbohydrate active enzymes (CAZy) and the intracellular metabolism. CAZy genes are responsible of encoding enzymes responsible of wood decomposition and the intracellular metabolism is responsible for converting the released sugars into ethanol and other metabolites. Changes in the CAZy gene expression led into changes, for instance, in cellulase activity under hypoxia. In addition, the substantial effect of hypoxia was extended in various intracellular metabolic pathways that were manifested as extracellular accumulation of ethanol and acetate. To conclude, the white-rot fungus P. radiata can decompose untreated lignocellulose in low-oxygen conditions and turn the released sugars into ethanol. Production of ethanol was also achievable on a larger than laboratory scale indicating that a “single-step, single-organism consolidated bioprocess” could be used as a novel method for bioethanol production.