CAROTENOIDS 



amount of pigment produced by Mycohact. phlei is conditioned by the 

 mineral constituents of the niedium. On a synthetic glucose-asparagine 

 medium production is stimulated by the addition of Fe ' * • and reduced 

 by K • or PO4' ' '. When glucose is replaced by glycerol the situation 

 is altered ; K ' has no effect, whilst PO4' ' ', Fe ' ' ' and Cu • '. all 

 decrease pigment formation. Turian^^" has recently broadly con- 

 firmed Ingraham and Steenbock's observations, but has separated 

 chromogenesis (carotenogenesis) from plasmogenesis ; using Ingraham 

 and, Steenbock's basal medium, he found that Fe * * * stimulated both 

 reactions but Mn * • specifically stimulated carotenogenesis. It is con- 

 sidered that the redox properties of these two metal ions are concerned 

 in their action. 



(iii) Inhibition Studies 



Turian«i has recently shown that diphenylamine added to the 

 culture medium at levels of 1/20,000-1/35,000, inhibits carotenoid 

 synthesis without inhibiting grov^h ; this inhibition is reversed by 

 Fe • • • (0-1 mg./lOO g.) but not by other ions. The effect of Fe • • * 

 may be of biological importance (as Turian is inclined to believe) or 

 it may be due to the fact that diphenylamine is rapidly oxidized in the 

 presence of Fe * * *. Diphenylamine is considered to act by inhibiting 

 oxidation (dehydrogenation) of the colourless carotenoids (phyto- 

 fluene, etc.) which may be precursors of the " true " carotenoids 

 As stated on p. 115, Goodvdn^^ has shown that the colourless caro- 

 tenoids do accumulate and the coloured carotenoids disappear when 

 the fungus Phycomyces blakesleeanus is grown on a medium containing 

 diphenylamine, but emphasized that this does not prove that phyto- 

 fluene and phytoene are precursors of ^-carotene, etc. 



Recently Turian «2b has shown that phenol (1/2,000-1/5,000) 

 also retards carotenogenesis in Mycohact. phlei ; resorcinol is about 

 2-3 times less active whilst a-naphthylamine, thiourea, KCN, salicylal- 

 doxime are almost inactive. Dinitrophenol (10-*), on the other hand, 

 stimulates the production of carotenoids. 



The carotene formation in Rhodohacillus palustris is independent of 

 the iron content of the medium. ^ ^ ° 



(iv) Effect of Light, Temperature, etc. 



The physical conditions affecting growth of Sarcina aurantiaca have 

 been investigated by Reader. ^ ^ This organism grew better at 20° 

 than at 37°, and although the yield of carotenoids was higher at 20°, 

 the concentrations were identical at both temperatures. The pH limits 



126 



