B12 SPECIFICITY OF MARINE CENTRIC DIATOMS1, 2

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Abstract
SUMMARY: Twenty‐one species (23 isolates) of marine diatoms were examined for their capacity to utilize analogs of cyanocobalamin for growth at the ecologically significant concentration of 4 ng 1‐1. Yields due to the analogs were compared to those produced by B12. Responses of the various clones to the analogs were not all‐or‐none, but varied continuously; thus, assigning the clones to the conventional B12 specificity types is a convenient but arbitrary classification. The use of 10 and 1% levels of response is suggested for such classification. At the 10% level of response, 11 clones had coliform, 4 lactobacillus, and 8 mammalian specificity patterns. At the 1% response level, 14 had coliform, 5 lactobacillus, and 4 mammalian specificities. All clones exceed the 10% response level on all benzimi‐dazole‐containine analogs tested. Few clones showed definite enough patterns of response to make them potentially useful for differential bioassay. The clones suggested are clone 675‐D (Bidclulphia sp.?), clone F;‐3 (Fragilaria sp.?), and the estuarine clone of Cyclotella nana (3H).