BIOASSAY OF SEAWATER: II. METHODS FOR THE DETERMINATION OF CONCENTRATIONS OF DISSOLVED VITAMIN B1 IN SEAWATER

Abstract

Methods for the bioassay of seawater for vitamin B1 (thiamine) using the marine chrysomonad, Monochrysis lutheri, are described. Cell counts after a 120-hour incubation or 14C-uptake rates after a 48- or 72-hour incubation were proportional to the vitamin B1 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 14C as Na214CO3 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 B1 concentrations which can be assayed was about 2–35 ng/l by 46-hour preincubation followed by 14C-uptake measurements or by counting cells after 120 hours. The range was extended to 100 ng B1/l after the 70-hour preincubation in the 14C-uptake method. These methods were capable of determining vitamin B1 in seawater at about one-tenth the level reported previously.