A novel genus of Scottish thraustochytrids and investigation of their capacity for the production of docosahexaenoic acid

Abstract

Omega-3 fatty acids, in particular docosahexaenoic acid (DHA), have been extensively studied for many decades for their health benefitting properties in pre-natal development, cardiovascular and Alzheimer diseases and enhancing the inflammatory immune response system. DHA has also been shown to be essential for the optimal development of fish, and therefore is an important ingredient in fish feed. However, due to fish oil and fish meal supplies currently facing many challenges (e.g. heavy metal contamination, environmental impacts, etc.), the demand for alternative sources of omega-3 fatty acids (FA) is predicted to rise in the near future. To meet these challenges, oleaginous microorganisms that produce omega-3 FAs have been explored as a potential new resource, with a particular emphasis on the thraustochytrid group. In this study, ten new strains of thraustochytrids, that were originally isolated from Scottish marine waters, were investigated for their biotechnological potential. The first phase of the project identified the new strains as a novel genus of thraustochytrid, for which the name Caledonichytrium matryoshkum gen. nov., sp. nov., is proposed. The description was based on a polyphasic analysis that employed phylogenetic analysis, biochemical signatures (PUFA and carotenoid profiles) and morphological and life cycle assessment studies. After identification, the strains were screened for their potential as DHA single-cell oil producers. The strains were assessed in two media types and at two time points of growth phase. With a view to their industrial application, a mathematical study was also included to seek opportunity for recycling by-product oil as biodiesel. The results showed that one of the strains, OL5TA, produced the highest relative level of DHA (63% of total FA) than any other strain reported to date in a screening study. However, the low final biomass concentrations reached (< 1 g L-1), and the low total lipid content measured (< 7% of dry cell weight, DCW), were considered major hurdles to overcome for industrial application. To address these issues, the optimisation of the culture conditions was carried out in the following stage. The results showed no consumption of glucose at 0.1% or 2% concentration, suggesting the inability of the strain to assimilate glucose. This may have hindered competitive biomass concentrations compared to that by other strains reported in the literature. To remediate this inability, a preliminary study was conducted to determine carbon source utilisation and carotenoid production to seek other routes for medium optimisation and biotechnological potential. The study concluded by identifying a potential route of exploitation for galactose and long carbon chain as sole carbon sources.