Investigating enzyme systems from deep-sea fungal secretomes for biological pre-treatment of cattle paunch contents and bioenergy production

Cattle paunch contents are the recalcitrant, lignocellulose-rich feed found in the rumen of cattle. To improve the microbial degradation of paunch solids during AD, pre-treatments can be effective. While physicochemical treatments can increase biomethane production from cattle paunch contents, biological pre-treatments e.g. enzymatic can require less energy, uncomplicated equipment and operating conditions, can be more targeted and controllable, recycling of chemicals after the treatment is unnecessary, downstream processing is low-cost, and there is very little, or no, inhibitor formation. Despite this, paunch contents have not been pre-treated biologically to-date outside of the rumen. Therefore, this thesis focused on developing a novel biological pre-treatment for cattle paunch contents, to improve their biodegradability during AD and thereby increase biomethane production. Lignocellulolytic fungal secretomes were characterised and applied in the saccharification of paunch contents, and were from strains of Emericellopsis maritima, Penicillium chrysogenum, P. antarcticum and Talaromyces stollii isolated from deep-sea sediments, an extreme environment, in the North Atlantic. Extremophiles can produce more robust proteins than those produced by their terrestrial counterparts, as a direct result of their inhospitable natural environment. The T. stollii SFI-F17 secretome demonstrated remarkable levels of exo-glycoside hydrolase activity, and was superior to the others in its ability to saccharify paunch contents. Therefore, the pre-treatment of three compositionally different lots of paunch contents was investigated using the T. stollii SFI-F17 secretome and/or rumen fluid, which is rich in lignocellulolytic microbes, to determine if they could improve the biomethane potential (BMP) of the paunch contents. A BMP test carried out over 50 days revealed that, when both rumen fluid and the T. stollii SFI-F17 secretome were used, the BMP increased by 104.68%, 104.84% and 83.24% compared to the controls. When pre-treated with just the T. stollii SFI-F17 secretome, the BMP increased by 44.58%, 74.47% and 101.35% compared to the controls. Finally, whole de novo shotgun sequencing of T. stollii SFI-F17 and characterisation of its Carbohydrate Active Enzyme (CAZy) repertoire showed that it encodes 605 CAZymes out of 11,458 genes, of which over 200 were predicted to be involved in lignocellulose degradation. These included 366 glycoside hydrolases (GHs), 115 glycosyl transferases (GTs), 28 carbohydrate esterases (CEs), 7 polysaccharide lyases (PLs), 78 auxiliary activities (AAs) and 84 carbohydrate-binding modules (CBMs).

Publisher

University of Galway

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CC BY-NC-ND

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University of Galway Theses (PhD Theses)