CAROTENOIDS IN PLANTS 



for growth were 5-30-9-43 with maximum production occurring at pH 

 7-15. There was no difference in pigmentation of cultures grown either 

 in the dark or diffuse dayhght. Bright Hght bleached coloured cultures 

 but the ability to produce pigment was not lost because pigmentation 

 was normal when subcultures of these bleached colonies were trans- 

 ferred to the dark. Ingraham and Steenbock'' found that light had 

 no appreciable effect on carotenoid formation in Mycohact. phlei, and 

 that carotenoids were produced by the Mycohact. phlei when cultured 

 at room temperature but not when the temperature was raised to 37°. 

 O2 reduces whilst light stimulates carotenogenesis in R. ruhrum.^^ 



(v) General 



Ingraham and Baumann" have stated that storage and utilization 

 of carotenoids and lipids run parallel in Mycohact. phlei. 



Recently a group of American workers 1^* have prepared a saline 

 extract of a chromogenic strain of Staph, aureus which stimulates 

 pigment (carotenoid) production in non-chromogenic strains of the 

 same bacterium. This extract does not give the colour reactions of 

 proteins but does give a slight positive test for pentose. 



In two paratubercle bacilli, B. lomhardo-pellegrini and B. boquet, the 

 degree of pigmentation (presumably mainly due to carotenoids, {see 

 p. 124) is directly proportional to the aneurin content of the 

 medium. ^ ^ ^a j^ should perhaps be noted that in these organisms 

 aneurin can be replaced by its pyrimidine moiety (2-methyl-4-amino- 

 5-aminomethylpyrimidine) for they have the ability to synthesize the 

 thiozole part of aneurin. 



In spite of all the work reported here it is obvious that the mechanism 

 of carotenoid formation in bacteria is just as obscure as in other organ- 

 isms, but Karrer et al. ^ ^ have suggested that formation from asparagine 

 and malic acid involves the conversion of these substrates into p- 

 methylcrotonaldehyde, which is a possible precursor of carotenoids 

 {see p. 64). No experimental support for this suggestion has yet 

 been forthcoming. 



FUNCTION OF CAROTENOIDS IN BACTERIA 



Very little work has been carried out in an effort to define the func- 

 tion of bacterial carotenoids. A possible role in photosynthesis appears 

 to have been ruled out in the case of the purple bacteria ^ ^ ' including 

 Spirillum ruhrum, ^ ^ * although French ^ ^ ^ has isolated, from a number 

 of photosynthetic bacteria, a protein complex photosynthin, which 



127 



