Bioassay of biotin and its distribution in the sea

A simple, rapid and sensitive method of microbiological assay for the determination of biotin in seawater has been developed by using a marine bacterium, Achromobacter sp. (Strain yH-51) as an assay organism. When the organism was incubated at 25°C for 48 h in a synthetic medium with constant shaking, a standard reference curve of bioassay was obtained. The organism is sensitive in the range 0.1 to 8.0 ng/l biotin. The distribution of biotin has been determined in the East China Sea, the North Pacific Ocean, and the bays and inlets along the Pacific coast of Japan. Biotin concentrations in surface waters were in the range from less than 0.1 ng/l up to 57.9 ng/l; generally high in coastal waters and low in deep open waters. The concentrations were generally high in surface waters, and rapidly decreased with depth down to 50 m, below which values were generally low. The vertical distribution of biotin followed closely the concentration of chlorophyll a, with high concentrations of biotin restricted to the euphotic layer of high chlorophyll a contents at most stations observed. Biotin concentrations in surface waters were generally high during summer, but in autumn and winter the concentrations decreased markedly.