New Australian thraustochytrids: A renewable source of Biofuels, Omega-¬¨‚â†‚ÄövÑv™3 oils and other bioproducts
thesisposted on 2023-05-27, 08:42 authored by Chang, KJL
The potential of biofuel production from microalgae is of intense interest globally owing to growing concern with rising crude oil prices and future availability. In addition to producing lipids for potential biofuel application, thraustochytrids are capable of forming other high-¬¨‚â†‚ÄövÑv™value bioproducts, such as proteins, enzymes, omega-¬¨‚â†‚ÄövÑv™3 polyunsaturated fatty acids (PUFA), carotenoid pigments and exopolysaccharides (EPS). The co-¬¨‚â†‚ÄövÑv™production of high-¬¨‚â†‚ÄövÑv™value bioproducts during biofuel production is desirable when it adds greater value to the production process and improves process economics. Thirty-¬¨‚â†‚ÄövÑv™six new thraustochytrids have been isolated from the southeast coast of Tasmania and far north Queensland. They were separated into eight chemotaxonomic groups (A ‚Äö- H) based on fatty acid and sterol composition, with the groups clustered closely with four different genera (Aurantiochytrium, Schizochytrium, Thraustochytrium and Ulkenia) based on 18S rDNA molecular identification. In an initial screening study, some strains produced > 60 % docosahexaenoic acid (DHA) under unoptimized culture conditions. Aurantiochytrium sp. strains (groups G and H) contained 15:0 (pentadecanoic acid) at between 20 ‚Äö- 30 % of the total fatty acids (TFA) and 16:0 (palmitic acid) in the range of 7 ‚Äö- 15 % TFA, suggesting these strains could be potential candidates for biodiesel production. ˜í‚â§,˜í‚â§-¬¨‚â†‚ÄövÑv™Carotene, canthaxanthin and astaxanthin were identified in pigmented strains. Part of the process to scale up is to select the best performing strain based on growth and biochemical characteristics. In the subsequent trials, eight thraustochytrid strains from the different chemotaxonomic groups (A ‚Äö- H) were compared in 1 L scale baffled shake flasks for the synthesis of EPS, in addition to biomass yield and fatty acid profiles. The crude chemical characterization of the EPS, which were released into the culture media by these strains, was performed as an initial step in determining the potential for biotechnological application of these biomaterials. Aurantiochytrium sp. strain TC 20 had the highest biomass production (18.5 g/L) and oil yield (7.5 g/L) after 9 days of growth in 4 % w/v glucose basal media at 20 ¬¨‚àûC, with 0.18 g/L EPS extracted from the supernatant. The maximum yield of EPS was observed in Schizochytrium sp. strain TC 02 (0.3 g/L). High biomass producing strains that also had high lipid and high EPS yield may be better candidates for commercial production of biofuels and other bioproducts. The next phase was to optimize biomass in 2 L bioreactors. The growth of Aurantiochytrium sp. TC 20 was also investigated using glycerol as a carbon source. Glycerol is becoming increasingly available, because it is a by-¬¨‚â†‚ÄövÑv™product of biofuel production from vegetable oil and animal fats. Fortification of the feed with additional nutrients improved the biomass yield from 56 g/L (34 % total fatty acids) to 71 g/L (52 % total fatty acids, cell dry weight) at 69 h. A life-¬¨‚â†‚ÄövÑv™cycle assessment, from the upstream biomass production to the direct emission of biodiesel combustion, was applied to assess the energy balance and the potential environmental impacts of this heterotrophic microalgal-¬¨‚â†‚ÄövÑv™derived biodiesel. The scenario analysis of a virtual production facility, modeled on experimental yield data, demonstrated that cultivation of heterotrophic microalgae for the production of biodiesel is comparable in terms of greenhouse gas emissions and energy usage to production of petroleum diesel. The LCA identified that improvements in cultivation conditions, in particular the bioreactor energy inputs and microalgae yield, will be critical in developing a sustainable production system. This study demonstrates the potential of heterotrophic cultivation of newly isolated endemic thraustochytrids to provide Australia's transportation fleet with a secure, environmentally sustainable alternative fuel feedstock, and co-¬¨‚â†‚ÄövÑv™production of high value bioproducts that can provide additional revenue to benefit the economics of biofuel production.
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