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Labyrinthulids and thraustochytrids are unicellular heterotrophs, formerly considered as fungi, but presently are recognized as members in the stramenopiles of the kingdom Protista sensu lato. We determined the 18S ribosomal RNA gene sequences of 14 strains from different species of the six genera and analyzed the molecular phylogenetic relationships. The results conflict with the current classification based on morphology, at the genus and species levels. These organisms are separated, based on signature sequences and unique inserted sequences, into two major groups, which were named the labyrinthulid phylogenetic group and the thraustochytrid phylogenetic group. Although these groupings are in disagreement with many conventional taxonomic characters, they correlated better with the sugar composition of the cell wall. Thus, the currently used taxonomic criteria need serious reconsideration.

The culture conditions for high‐yield production of docosahexaenoic acid (DHA) by Schizochytrium sp. strain SR21 were investigated in a fermenter. With increasing carbon (glucose) and nitrogen (corn steep liquor and ammonium sulfate) sources (up to 12% glucose) in the medium, DHA productivity increased without a decrease in growth rate, i.e., 2.0, 2.7, and 3.3 g DHA/L/d with 6, 10, and 12% glucose, respectively. Eventually, 48.1 g dry cells/L and 13.3 g DHA/L were produced in 4 d with 12% glucose. DHA productivity was decreased with 15% glucose, i.e., 3.1 g/L/d. With 12% glucose, the lipid content was 77.5% of dry cells, and DHA content was 35.6% of total fatty acids. The lipid was composed of about 95% neutral lipid and 5% polar lipid. In polar lipids, the contents of phosphatidylcholine (PC), phosphatidylethanolamine, and phosphatidylinositol were 74, 11, and 5%, respectively. The PC profile was simple, 70% of PC molecules were 1‐palmitoyl‐2‐DHA‐PC and 1.2‐di‐DHA‐PC. These results indicate that Schizochytrium sp. strain 21 is an excellent source for microbial DHA production, including not only the acid form of DHA but also 2‐DHA‐PC.

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A marine microbe (strain SR21) from the coral reef area of the Yap Islands was isolated by a screening test for polyunsaturated fatty acids and was found to accumulate lipid that contained 22:5n‐6 docosapentaenoic acid (DPA) as well as 22:6n‐3 docosahexaenoic acid (DHA). Strain SR21 was identified as genusSchizochytrium in Labyrinthulomycota, owing to its ultrastructural character and life cycle, which is composed of vegetative cell, zoosporangium, and zoospore stages. After cultural optimization, both in flask and fermenter, the highest DHA and DPA productivities of 2.0 and 0.44 g/L per day, respectively, were obtained in a medium of 60 g/L glucose and corn steep liquor/ammonium sulfate in a half salt concentration of seawater in fermenter culture at 28°C and pH 4. This productivity was almost twice that obtained with flask culture, indicating its high resistance to mechanical stirring. The lipid extracted from the cell was about 50% of the dry cell weight and was composed of 93% triacylglycerol (TG). DHA content of the lipid was 34% of total fatty acids. The TG profile was simple, and the content of the most dominant TG, 1,3‐dipalmitoyl‐2‐DHA‐TG, was 27%. TG that contained DHA and n‐6‐DPA amounted to 57 and 17%, respectively, of total TG molecules. Strain SR21 was revealed to be an excellent source of microbial DHA and n‐6 DPA.

Strong (10-T) SMFs have no effect on cell growth, cell cycle distribution, or micronucleus frequency, but they may cause an increase in the micronucleus formation induced by 4-Gy x rays.

Me 2 SO is a polar solvent that is widely used in biochemistry, pharmacology, and industry. Although there are several reports in the literature concerning the biological effects of Me 2 SO, the total cellular response remains unclear. In this paper, DNA microarray technology combined with the hierarchical clustering bioinformatics tool was used to assess the effects of Me 2 SO on yeast cells. We found that yeast exposed to Me 2 SO increased phospholipid biosynthesis through up-regulated gene expression. It was confirmed by Northern blotting that the level of INO1 and OPI3 gene transcripts, encoding key enzymes in phospholipid biosynthesis, were significantly elevated following treatment with Me 2 SO. Furthermore, the phospholipid content of the cells increased during exposure to Me 2 SO as shown by conspicuous incorporation of a lipophilic fluorescent dye (3,3 -dihexyloxacarbocyanine iodide) into the cell membranes. From these results we propose that Me 2 SO treatment induces membrane proliferation in yeast cells to alleviate the adverse affects of this chemical on membrane integrity.Dimethyl sulfoxide (Me 2 SO) 1 is widely used as a solvent in the chemical industry and as a cryoprotectant in biotechnology. It is present in the environment as a waste product of the paper industry and from the production of dimethyl sulfide (DMS) and also arises from the degradation of sulfur-containing pesticides (1). In addition, Me 2 SO forms naturally from photooxidation of DMS in the atmosphere and from degradation of DMS by phytoplankton in the marine environment (2). Because Me 2 SO has low volatility and is highly hygroscopic, it is rapidly scavenged from the atmosphere by rain and returned to earth, and thereby plays a role in the global sulfur cycle (1, 3).Microorganisms, including both prokaryotes and eukaryotes, have the capability of reducing Me 2 SO and can utilize it as a terminal electron acceptor during anaerobic growth (4 -6). Me 2 SO reductase from Escherichia coli and Rhodobacter sphaeroides catalyzes the reduction of Me 2 SO to DMS (7-9). This enzyme, which contains a molybdenum cofactor at the active center, is well characterized at the biochemical, biophysical, and molecular level and provides an excellent model system for investigating the structure and mechanism of electron transfer chain complexes (1, 10). Saccharomyces cerevisiae has a number of NADPH-dependent enzymes that, in conjunction with methionine sulfoxide reductase (MXR1), can reduce Me 2 SO to DMS (11).In E. coli, the combination of divalent cations as Ca 2ϩ and Me 2 SO has been shown to stimulate the efficiency of DNA transfer into the cell (12). In the case of mammalian cells, it is reported that the transfection efficiency is increased by Me 2 SO treatment after electroporation (13). The exact mechanism of how Me 2 SO increases membrane permeability leading to DNA uptake is unclear.In mammalian cells Me 2 SO (2% (v/v)) can induce morphological changes, for example in mouse erythroleukemic cells (14), or cause differentiation, for example ...

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