The free-living, hermaphroditic nematode Caenorhabditis briggsae has a nutritional requirement for sterols. It will reproduce indefinitely in a liquid medium containing only bacterial cells (Escherichia coli) and salts if various sterols are present. Several other lipid-soluble materials are ineffective in supporting reproduction.

The free-living hermaphroditic nematode Caernorhabditis briggsae has a nutritional requirement for heme. The organism can be subcultured repeatedly in a chemically defined axenic medium that contains autoclaved bacterial cells (Escherichia coli) and sterols if a hemeprotein-containing fraction from liver is present. Pure myoglobin, hemoglobin, cytochrome c, and hemin, respectively, can substitute effectively for the liver fraction.

The roles of dietary vitamin B12 and folic acid in methionine biosynthesis from homocysteine were first observed in higher animals. Jukes, Stokstad, and Broquist (1) noted that the growth of vitamin BIZ-deficient chicks was increased by either methionine or homocysteine and vitamin B,, but not by homocysteine alone. It was also reported that rats were able to utilize homocysteine in lieu of methionine when folic acid (2) or choline (3) was added to the diet. In microorganisms, Escherichia coli is known to possess two alternative pathways for methionine biosynthesis: the vitamin B,,-dependent pathway (4) and the vitamin BIZ-independent one ( 5 ) . In the present study, we show evidence that dietary vitamin Blz and folic acid are required for the biosynthesis of methionine from homocysteine in an axenic free-living nematode, Caenorhabditis briggsae . Information related to biochemical nutrition in invertebrates is sparse. Therefore, this study has particular relevance to the fields of comparative nutrition and biochemistry.Materials and methods. Composition of the basal medium. The chemical-defined medium Caenorhabditis briggsae maintenance medium (CbMM) (6) was specially prepared by the Grand Island Biological Company (Grand Island, New York) and supplied as a sterile, double-strength solution. Several of those chemical components which are normally present in the standard medium were deleted from the special medium: vitamin BIZ, folic acid, calcium folinate (5-formyltetrahydrofolic acid), L-methionine, choline dihydrogen citrate , gluta-

Ellsworth Dougherty was a man of impressive intellectual dimensions and interests; in a relatively short career he contributed enormously as researcher and scholar to the biological knowledge base for selection of Caenorhabditis elegans as a model organism in neurobiology, genetics, and molecular biology. He helped guide the choice of strains that were eventually used, and, in particular, he developed the methodology and understanding for the nutrition and axenic culture of nematodes and other organisms. Dougherty insisted upon a concise terminology for culture techniques and coined descriptive neologisms that were justified by their linguistic roots. Among other contributions, he refined the classification system for the Protista.

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