Assessment of different nitrogen sources and bioreactor cultivation strategies during growth of Aurantiochytrium limacinum on spruce sugars

Heterotrophic microbial production of omega-3 fatty acids for feed and food applications is an attractive alternative to the use of fish oils. In this study we have converted enzymatic hydrolysates of wood to oils rich in DHA by applying Aurantiochytrium limacinum SR21 in controlled bioreactor fermentation processes. FTIR was used as a rapid method to evaluate the effects of dissolved oxygen (DO), C/N ratios, and nitrogen sources on protein-to-lipid ratios in the produced microbial biomass. A biomass concentration of 21.7 g/L containing 29.1 % total fatty acid (TFA), out of which 35.1 % was docosahexaenoic acid (DHA), was obtained in batch cultivations using 20 % DO, a medium C/N ratio of 10gC/gN and a 50: 50 blend of complex organic nitrogen, in the form of yeast extract and peptone, and NaNO3. A continuous cultivation strategy (D = 0.3 day-1) led to much lower biomass and lipid titers compared to a batch process, indicating that a single vessel chemostat set-up may not be suitable for lipid production by A. limacinum SR21.