86 THE METABOLISM OF ALGAE 



caeca, Chilotnonas paramoecium'^^^ and Prototheca zopfii}^ 

 A mutant requiring thiamine of Chlamydomofias moewusii 

 has been induced by ultra-violet irradiation and responds to 

 as little as io~^'^ gm./ml. of the substance. Here it is the 

 pyrimidine portion alone which is required, the ability to 

 synthesize thiazole remaining unimpaired. ^'^'^ 



The requirement of Euglena gracilis for thiamine is of 

 particular interest in that this substance has been found to 

 be necessary for phototrophic growth but not when gluta- 

 mate is supplied either in the light or the dark.^^ The sig- 

 nificance of these facts is not clear since although it is 

 possible for the decarboxylation of pyruvic acid, for which 

 thiamine is essential, to be by-passed if glutamate is the 

 carbon source (see Fig. lo), thiamine appears to be just as 

 necessary for the oxidative decarboxylations occurring in 

 the tricarboxylic acid cycle, which presumably operates in 

 Euglena. Possibly the inability of Euglena gracilis to synthe- 

 size thiamine is not absolute and glutamate exerts sufficient 

 thiamine-sparing action to enable growth to take place. 



Traces of vitamin Bjg, the anti-pernicious anaemia 

 factor of animals, are necessary for the growth of Euglena 

 gracilis, E. stellata and Astasia spp. It has been suggested 

 that the requirement is characteristic of species of Eugle- 

 nineae in general, but it can also occur in representatives of 

 other classes, e.g. Chlamydomonas chlamydogama}^^ Vita- 

 min Bi2, like folic acid, may be concerned in the synthesis 

 of desoxyribosenucleic acid.^^*' The vitamin B12 require- 

 ment of Euglena gracilis is the same whether grov^th takes 

 place in the light or in the dark.*^ 



A constituent of folic acid, /)-amino-benzoic acid, has 

 been recognized as an essential metabolite as a result of the 

 observation that it antagonizes the inhibition of the growth 

 of micro-organisms by its analogue, sulphanilamide.^®^ 

 p-Amino-benzoic acid evidently plays as important a role 

 in the metabolism of some algae as it does in that of other 

 organisms since it has been found to neutralize the inhibi- 

 tory effects of sulphanilamide on the growth of Nitzschia 

 spp.^^*^ and of Chlamydomonas ffioewusii.^'^'' While p-amino- 

 benzoic acid has been found to be a growth factor for several 



