Impact of low-intensity pulsed ultrasound on the growth of Schizochytrium sp. for omega-3 production.

Schizochytrium sp. is a microalga that is known for its high content of oils or lipids. It has a high percentage of polyunsaturated fatty acids in the accumulated oil, especially docosahexaenoic acid (DHA). DHA is an important additive for the human diet. Large-scale production of Schizochytrium sp. can serve as an alternative source of DHA for humans as well as for fish feed, decreasing the burden on aqua systems. Therefore, research on improving the productivity of Schizochytrium attracts a lot of attention. We studied the potential of using low-intensity pulsed ultrasound (LIPUS) in the growth cycle of Schizochytrium sp. in shake flasks. Different intensities and treatment durations were tested. A positive effect of LIPUS on biomass accumulation was observed in the Schizochytrium sp. culture. Specifically, LIPUS stimulation at the ultrasound intensity of 400 mW/cm2 with 20 min per treatment 10 times a day with equal intervals of 2.4 h between the treatments was found to enhance the growth of Schizochytrium biomass most effectively (by up to 20%). Due to the nature of cell division in Schizochytrium sp. which occurs via zoospore formation, LIPUS stimulation was inefficient if applied continuously during all 5 days of the growth cycle. Using microscopy, we studied the interval between zoospore formation in the culture and selected the optimal LIPUS application days (Days 0-1 and Days 4-5 of the 5-day growth cycle). Microscopic images have also shown that LIPUS stimulation enhances zoospore formation in Schizochytrium sp., leading to more active cell division in the culture. This study shows that LIPUS can serve as an additional tool for cost-efficiency improvement in the large-scale production of Schizochytrium as a sustainable and environmentally friendly source of omega-3 (DHA).

Strategic Development of Aurantiochytrium sp. Mutants With Superior Oxidative Stress Tolerance and Glucose-6-Phosphate Dehydrogenase Activity for Enhanced DHA Production Through Plasma Mutagenesis Coupled With Chemical Screening.

Thraustochytrids, such as Aurantiochytrium and Schizochytrium, have been shown as a promising sustainable alternative to fish oil due to its ability to accumulate a high level of docosahexaenoic acid (DHA) from its total fatty acids. However, the low DHA volumetric yield by most of the wild type (WT) strain of thraustochytrids which probably be caused by the low oxidative stress tolerance as well as a limited supply of key precursors for DHA biosynthesis has restricted its application for industrial application. Thus, to enhance the DHA production, we aimed to generate Aurantiochytrium SW1 mutant with high tolerance toward oxidative stress and high glucose-6 phosphate dehydrogenase (G6PDH) activities through strategic plasma mutagenesis coupled with chemical screening. The WT strain (Aurantiochytrium sp. SW1) was initially exposed to plasma radiation and was further challenged with zeocin and polydatin, generating a mutant (YHPM1) with a 30, 65, and 80% higher overall biomass, lipid, and DHA production in comparison with the parental strains, respectively. Further analysis showed that the superior growth, lipid, and DHA biosynthesis of the YHMP1 were attributed not only to the higher G6PDH and enzymes involved in the oxidative defense such as superoxide dismutase (SOD) and catalase (CAT) but also to other key metabolic enzymes involved in lipid biosynthesis. This study provides an effective approach in developing the Aurantiochytrium sp. mutant with superior DHA production capacity that has the potential for industrial applications.