MINIMUM CYANOCOBALAMIN REQUIREMENTS OF SOME MARINE CENTRIC DIATOMS1

Abstract

The minimum amount of cyanocobalamin for production of one µ 3 of cell was estimated for 7 clones of marine centric diatoms isolated from estuarine, neritic, and oceanic environments. The number of molecules of B 12 per µ 3 varied from 5 to 18.4; thus the diatoms have about the same requirement as do other organisms. The neritic species Skeletonema costatum became structurally abnormal in vitamin‐depleted cultures. The possibility is raised that B 12 concentration is important at certain times in the diatom life cycle ( e.g., spore formation); hence for a given species the time at which the vitamin is present in suitable concentration may be more significant than the total quantity available during the period of growth of a population.