Thraustochytrids, marine protists whose dominant genera are Thraustochytrium and Schizochytrium, belong to the kingdom Chromista and are known as an industrial source of DHA. We describe here that thraustochytrid strain KH105, isolated as a DHA producer, also accumulates significant levels of β-carotene and xanthophylls including canthaxanthin and astaxanthin. A 4-d cultivation using a medium composed of 10% glucose and less than 0.3% of nitrogen sources in a half-concentration of seawater gave an astaxanthin production up to 6.1 mg/L, and canthaxanthin content reached more than 10 mg/L under conditions where a higher concentration of nitrogen sources (6%) was employed. It might be advantageous in mass production systems for these carotenoids to be extracted readily by simply suspending the cells with organic solvents such as acetone and chloroform. Analyses on the morphological and life history features of the KH105 strain revealed that it belongs to the genus Schizochytrium. This particular species of thraustochytrids is thus considered to be a promising source of xanthophylls as well as DHA for use in the food industry.Paper no. J10395 in JAOCS 80, 789-794 (August 2003).
More than 300 strains of microorganisms producing polyunsaturated fatty acids (PUFA) were newly isolated from coastal seawater in the Seto Inland Sea and around Iriomote Island, Japan, by the baiting method. The profiles of PUFA from docosahexaenoic acid (DHA)-producing strains could be classified into four types. A strain, named KK17-3, was chosen for further study owing to its high DHA content (52.1% of total fatty acid) and wide range of PUFA (76.1%) including arachidonic, eicosapentaenoic, and docosapentaenoic acids as well as DHA. Glucose and tryptone were the optimal carbon and nitrogen sources, respectively, in a medium with salinity at 75% that of seawater. The PUFA contents in polar lipids (22.1% of total lipid), in which the DHA content was 39.3%, were higher than those in neutral lipids and glycolipids. Molecular phylogenetic analysis of 18S rRNA gene sequences showed KK17-3 to be a thraustochytrid. It also was observed to possess a life cycle composed of vegetative cells without successive bipartition, zoosporangium, and zoospore stage. Classification by the chemotaxonomic criterion based on PUFA compositions also supported this assignment.Paper no. J9874 in JAOCS 78, 605-610 (June 2001).KEY WORDS: 18S rRNA gene, docosahexaenoic acid, molecular phylogenetic analysis, polyunsaturated fatty acid, Thraustochytrium.Polyunsaturated fatty acids (PUFA) with unique structural characteristics are distinguished by their functions not only in regulating cell physiology such as phase transition, membrane permeability and the behavior of membrane-bound proteins (1) but also in modulating the expression of certain genes (2). Therefore, it is not surprising that PUFA deficiencies lead to abnormalities in the skin, kidney, nervous network, immune and inflammatory reactions, cardiovascular system, endocrine control, and respiratory and reproductive systems (3,4). In particular, docosahexaenoic acid (DHA, C22:6n-3) is absolutely essential to humans owing to its functions in the brain and retina (5).The traditional commercial sources of PUFAs are fish oils. The relatively low proportion of PUFA in fish oils makes it difficult to produce DHA and other PUFA on a large scale. On that account, exploration of other sources of DHA as well as of other PUFA has drawn much research attention. To date, marine microorganisms belonging to achromatic stramenopiles such as thraustochytrids and labyrinthulids have been reported to produce significant quantities of DHA (3,6-14). Their different profiles of PUFA reflect taxonomic relationships. Molecular phylogenetic analysis (15,16) suggests that several regulatory mechanisms for PUFA biosynthesis exist in distinctive DHA-producing microbes. DHA can be synthesized by the conversion of arachidonic acid (AA, C20:4n-6), eicosapentaenoic acid (EPA, C20:5n-3), or docosapentaenoic acid (DPA, C22:5n-6) through their desaturation and elongation, catalyzed by fatty acid desaturases and elongases (3). It is desirable to obtain PUFA producers that accumulate not only DHA but also the intermediate...
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