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Fourcounts were made on the standards, counting cells in each.Many cells are enlarged when their growth is halted by vitamin B depletion.These valu es are subject to some underestimation because of the smaller yield of cells with pseudovitamin B as compared to theother forms.Figures and show standard cu rves for the two algae from one set of bioassays.Counts of replicate samples were as close as duplicate counts from the same tube.Dividing cells are also more difficult to designate.Dilutions for the cobamide assay should be selected using the assumption thatcobamide concentrations will be three times the B concentration.Wa tersamples from estuariesor shallow coastal regions must be diluted for bo th assays.Itis preferable to continue storing the water samples frozen, where they remain stable, if bioassay cultures cannotbe inoculated within abouta week after preparation.Workers using different techniques to study specificity report different results, so further standardization of methods would be required. The differentiation between pseudovitamin B and factor B in samples is dependent on having a clone responding to vitamin B and to pseudovitamin B only. Such a lactobacilluslike response is relatively rare.Among marine diatoms most clones capable of using pseudovitamin B can utilize factor B also.Of four clones having the appropriate lactobacillus response, only one produced sufficient yield of cells with pseudovitamin B to be suitable for assay use. Itwas used in preliminary assay work before being lost by accident from the culture collection.However, we do not know yet of any naturally abundantalgae thatcan utilize pseudovitamin B and not factor B.The different specificity of vitamin B response in marine algae suggests physiological differences which could be important in selection of the speciesor clones where low concentrations of vitamin B and its analogs occur.Ourobservation thatconcentrations of analogs exceed those of the vitamin indicate thatthe capacity to utilize analogs could be an advantage to a particular clone.High concentrations of analogs also suggest thatthe differential productionof vitamin B and its analogs by some microorganisms and the utilization of the vitamin and analogs by other microorganisms is a <a href="http://www.targetmol.com/compound/Halobetasol-Propionate"></a> complicated process., in Methodsof Biochemical Analysis, D. Limnol. Oceanogr. Received: November. Of additional cultures of diverse origin, showed stimulation by visible comparison of growth in tubes; nonquantitative comparisons, however, were not reliable for showing differences in growth of this organism.Different materials in the mixtures were undoubtedly responsible for some of the stimulation, because of the differences in composition of many of the defined basal culture media employed.The details of methods and results were not available., SPHAEROTILUS AND CYANOCOBALAMIN tion of. For the visual estimation of growth response, ml of glycerol glutamate broth per tube were used.One set of tubes was prepared without cyanocobalamin; the other contained m,ug of cyanocobalamin per ml.The five strains used for the quantitative determinations were also tested for formation of zones of increased growth around paper discs containing a solution of cyanocobalamin on glycerol glutamate agar plates.Stock solutions of cyanocobalamin were prepared from sterile solution of crystalline vitamin purchased in ampoules. of the broth to be inoculated.Because these cultures produced   little growth, cultures to be studied in modifications of the glutamate medium were similarly grown in CGY broth, washed twice with distilled water, and made up to original volume with distilled water.

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