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.

The use of chitosan as a flocculant has become a topic of interest over the years due to its positively charged polymer and biodegradable and non-toxic properties. However, most studies only focus on microalgae and wastewater treatment. This study provides crucial insight into the potential of using chitosan as an organic flocculant to harvest lipids and docosahexaenoic acid (DHA-rich Aurantiochytrium sp. SW1 cells by examining the correlation of flocculation parameters (chitosan concentration, molecular weight, medium pH, culture age, and cell density) toward the flocculation efficiency and zeta potential of the cells. A strong correlation between the pH and harvesting efficiency was observed as the pH increased from 3, with the optimal flocculation efficiency of >95% achieved at a chitosan concentration of 0.5 g/L at pH 6 where the zeta potential was almost zero (3.26 mV). The culture age and chitosan molecular weight have no effect on the flocculation efficiency but increasing the cell density decreases the flocculation efficiency. This is the first study to reveal the potential of chitosan to be used as a harvesting alternative for thraustochytrid cells.

Thraustochytrids are well-known for their ability to produce a variety of fatty acids, including polyunsaturated fatty acids (PUFAs), saturated fatty acids (SFA), odd-chain fatty acids (OCFA), as well as terpenoids such as squalene and carotenoids. However, despite Malaysia's extensive mangrove ecosystems, there have been limited studies on the diversity and potential of these microorganisms to produce fatty acids and terpenoids. In this study, we have isolated and screened oleaginous thraustochytrids capable of producing PUFAs and terpenoids from the mangrove ecosystem at Kelanang, Selangor, Malaysia. Nine dominant thraustochytrid strains with distinct macroscopic and microscopic characteristics were further cultivated in three different types of medium: YEP, GY, and BURJA and the impact of these media on the production of fatty acids, squalene, and carotenoids were evaluated. All isolates exhibited significant production of docosahexaenoic acid (DHA) and palmitic acid (C16:0). The highest DHA and C16:0 yields were observed in isolate S1 grown in YEP medium (50.89%) and in isolate S10 grown in GY medium (69.03%), respectively. Additionally, isolate S13 demonstrated a remarkable capacity for pentadecanoic acid (C15:0) production, reaching nearly 15% of total fatty acids (w/w) when cultivated in GY medium. Squalene production reached up to 652.38 mg L^-1 in isolate S5, while isolate S10 emerged as the highest carotenoid producer, yielding 1.77 mg L^-1 in GY medium. Isolates S5 (Thraustochytrium striatum strain S5), S1 (Aurantiochytrium limacinum strain S1), and S10 (Thraustochytrium kinnei strain S10) show promising potential for further optimisation and industrial applications in the sustainable production of high value bioproducts such as lipids, DHA, squalene, and carotenoids.

Thraustokaitrid seperti Aurantiochytrium sp. telah menarik perhatian penyelidik dan industri disebabkan kebolehannya untuk menghasilkan asid lemak politaktepu (PUFA) bernilai tinggi terutamanya asid dokosaheksaenoik (DHA, C22:6 ω-3). Namun begitu, keperluan penggunaan substrat yang mahal khususnya sumber karbon tulen semasa proses pengkulturan telah menyumbang kepada peningkatan kos pengkomersialan DHA daripada thraustokaitrid. Oleh itu, dalam kajian ini, potensi penggunaan sisa kulit nanas (SKN) yang merupakan antara sisa utama industri pertanian di Malaysia sebagai sumber karbon alternatif yang lebih murah untuk penghasilan DHA daripada Aurantiochytrium sp. SW1 telah dikaji. Memandangkan SKN mengandungi lignin, selulosa dan hemiselulosa yang agak kompleks, kaedah perawatan autoklaf, berasid dan beralkali pada kepekatan berbeza telah ditentukan bagi mendapatkan gula jumlah yang optimum daripada SKN. Hasil menunjukkan perawatan autoklaf secara signifikan (p<0.05) menghasilkan hidrolisat dengan kepekatan gula tertinggi (39.6 ± 1.98 g/L) berbanding dengan perawatan berasid dan alkali yang masing-masing dapat mengekstrak dalam julat 31-38 g/L gula jumlah. Kemudian, kebolehan Aurantiochytrium sp. SW1 untuk menggunakan kesemua hidrolisat SKN sebagai sumber karbon alternatif dibandingkan. Didapati, penggunaan hidrolisat SKN dengan rawatan 100 mM H2SO4 bersama nutrien tambahan secara signifikan (p<0.05) menghasilkan biojisim tertinggi (7.74 g/L ± 0.39) manakala kandungan lipid terbaik (60.7% ± 3.04) terhasil apabila SW1 dikulturkan menggunakan hidrolisat SKN dengan rawatan autoklaf tanpa penambahan nutrien. Penghasilan DHA yang maksimum (0.68 ± 0.034 g/L) dicapai apabila Aurantiochytrium sp. SW1 dikultur menggunakan hidrolisat SKN dengan rawatan 100 mM H2SO4 bersama nutrien tambahan yang mana 10-35% lebih tinggi jika dibandingkan dengan penghasilan menggunakan hidrolisat SKN yang lain. Kajian ini dapat menjadi asas ke arah penghasilan DHA yang lebih murah daripada thraustokaitrid dengan menggunakan SKN sebagai sumber karbon alternatif.