PLANKTON 39 



oxidation of pyruvic acid, there is also some alternative participation in 

 the Krebs tricarboxylic acid cycle, as in vertebrate tissues. For this re- 

 action, the co-carboxylase thiamin pyrophosphate must be present. An 

 example is the great enhancement of pyruvic acid oxidation by the addi- 

 tion of thiamin to the thiamin _ deficient Prototheca. If Vitamin B x is not 

 present as such in the aqueous nutrient, it must be synthesized by the algae. 

 Most are capable of so doing, but some cannot synthesize the thiazole, 

 others the pyrimidine, radicles of thiamin. Thus the thiazole portion must 

 be supplied to Polytomella ocellata, and the pyrimidine component to 

 Euglena gracilis and to a radiation mutant of Chlamydomonas moewusii. 

 The pyrimidine-thiamin requirement of the Euglena can be markedly de- 

 creased by the addition of glutamate. Both thiazole and pyrimidine must 

 be supplied exogenously for the growth of Polytomella caeca, Chilomonas 

 paramoecium, and Prototheca zopfi. 



Riboflavin, like thiamin, has been demonstrated in practically all algae 

 in which it has been sought. It is a component of the prosthetic group of 

 the flavo-proteins, but its essentiality to algal growth has not been shown. 

 Para-aminobenzoic acid is known to be necessary for the growth of only 

 one alga, a mutant of Chlamydomonas moewusii. With the latter and 

 with Nitzschia, para-a?ninobenzoic acid has the same antagonism to sul- 

 fonamide inhibition of growth as with many bacteria. Aniline may replace 

 para-aminobenzoic acid as a growth factor for Chlamydomonas with an 

 efficiency of one per cent, but it does not neutralize the sulfonamide 

 effect. 40 ' 227 



Plankton paste contains considerable quantities of cyanocobalamin or 

 Vitamin B 12 . 40,41 ' 228 Traces of this substance are necessary for the growth 

 of various Euglenineae as well as other classes, such as Chlamydomonas 

 chlamydogama of the Chlorophyceae. Vitamin B 12 may be concerned in 

 the synthesis of desoxyribosenucleic acid. 



Ascorbic acid is present in phytoplankton (especially Chlorella) in 

 amounts comparable to those in lemon juice; however most of it is lost in 

 drying and storage. Although little is said about the Vitamin D content 

 of microalagae, feeding experiments have indicated good antirachitic 

 activity. Indirect evidence comes from the potency of fish liver oils, which 

 ultimately derive their Vitamin D from planktonic sources. 229 As with 

 seaweeds, the vitamin activity of phytoplankton is based upon ergosterol 

 content. Substances with coagulant effect have been demonstrated by Dam, 

 who determined the Vitamin K content of Chlorella as six gamma per 

 gram of dried material. 230 



Phytoplankton has a great potential as a source of vitamins in human 



