Aurantiochytrium limacinum BUCHAXM 122, a strain of thraustochytrid microorganism is potentially an alternative source of essential nutrients for commercial products. In this study, the strain was screened for its characterization and determination of polyunsaturated fatty acid (PUFA) production. Cells were isolated from fallen mangrove leaves, and grown in a glucose-yeast extract-peptone (GYP) medium. Their morphology, life cycle, biomass, fatty acid, extracellular enzymes and major elements were also investigated. Colonies occurred prominently on the fourth day of cultivation, appearing opaque white in color and containing large numbers of amoeboid cells. These thraustochytrids were observed to have a multi-stage life cycle, developing through zoospore, vegetative and zoosporangium stages with a life span of approximately 24 h. Zoospores developed into vegetative cells within 10-12 h and vegetative cells developed into zoosporangia, releasing zoospores, within approximately 10-15 h. Results showed that A. limacinum BUCHAXM 122 produced highest biomass at 108 h, with 23.85 ± 1.02 g/l dry weight. The isolates had high content of docosahexaenoic acid (DHA; 30.31 ± 5.88% of total fatty acids), indicating that they could serve as a fatty acid source for human consumption and aquaculture feeds. Major elemental analysis showed that cells contained 57% carbon, 29% oxygen, 9% hydrogen, 4% nitrogen and 1% sulfur. Extracellular degradative enzymes including protease, lipase, urease, α-glucosidase and phosphatase activities were also detected.

This study aimed to develop bioreactors for cultivation of thraustochytrid, Aurantiochytrium limacinum BUCHAXM 122, that are low in cost and simple to operate. Obtaining maximum biomass and fatty acid production was a prerequisite. Three bioreactor designs were used: stirred tank bioreactor (STB), bubble bioreactor (BB) and internal loop airlift bioreactor (ILAB). The bioreactors were evaluated for their influence on oxygen mass transfer coefficient (kLa), using various spargers, mixing speed, and aeration rates. Biomass and DHA production from STB, BB, ILAB were then compared with an incubator shaker, using batch culture experiments. Results showed that a bundle of eight super-fine pore air stones was the best type of aeration sparger for all three bioreactors. Optimal culture conditions in STB were 600 rpm agitation speed and 2 vvm aeration rate, while 2 vvm and 1.5 vvm aeration provided highest biomass productivity in BB and ILAB, respectively. Antifoam agent was needed for all reactor types in order to reduce excessive foaming. Results indicated that with optimized conditions, these bioreactors are capable of thraustochytrid cultivation with a similar efficiency as cultivation using a rotary shaker. STB had the highest kLa and provided the highest biomass of 43.05 ± 0.35 g/L at 48 h. BB was simple in design, had low operating costs and was easy to build, but yielded the lowest biomass (27.50 ± 1.56 g/L). ILAB, on the other hand, had lower kLa than STB, but provided highest fatty acid productivity, of 35.36 ± 2.51% TFA.