Bioassay of Seawater: Ii. Methods for the Determination of Concentrations of Dissolved Vitamin B₁ in Seawater

Methods for the bioassay of seawater for vitamin B 1 (thiamine) using the marine chrysomonad, Monochrysis lutheri, are described. Cell counts after a 120-hour incubation or 14 C-uptake rates after a 48- or 72-hour incubation were proportional to the vitamin B 1 concentrations in seawater. Samples of seawater were supplemented with nutrients, filter-sterilized, and, if necessary, diluted with medium prepared in charcoal-treated seawater. External and internal standards were used. A starved culture of M. lutheri was added and the assay-flasks were incubated in the light for 46 or 70 hours, after which 14 C as Na 2 14 CO 3 was added and its uptake was measured after 2 hours. Cell counts were made after 120 hours. Most of the samples bioassayed to date showed no inhibition to the alga. The range of vitamin B 1 concentrations which can be assayed was about 2–35 ng/l by 46-hour preincubation followed by 14 C-uptake measurements or by counting cells after 120 hours. The range was extended to 100 ng B 1 /l after the 70-hour preincubation in the 14 C-uptake method. These methods were capable of determining vitamin B 1 in seawater at about one-tenth the level reported previously.