Requirement for Thiamine Among Some Marine and Supra-Littoral Protista

The requirement for thiamine was examined in eleven marine protists of littoral, supra-littoral or neritic origin. Six were found to have an absolute requirement for the vitamin. The thiamine-requiring Chrysophyta responded to the pyrimidine half of the vitamin, whereas the two thiamine-requiring Pyrrophyta responded to the thiazole half. All the species requiring thiamine were auxotrophic with respect to at least one other factor (usually vitamin B12). For half-maximal growth, species responding to pyrimidine required 100–300 mμg/1. pyrimidine or thiamine and species responding to thiazole 2000 mμg/1. thiazole or thiamine.