Photoreduction in Ochromonas malhamensis* 



WOLF VISHNIAC and GEORGE H. REAZIN, JR., Department of Microbi- 

 ology, Yale University, New Haven, Connecticut, and Research Department, 

 Joseph E Seagram & Sons, Inc., Louisville, Kentucky 



The chrysophyte flagellate Ochromonas malhamensis has been 

 isolated and grown in pure culture by Pringsheim (1), and a synthetic 

 medium for its cultivation has been devised by Hutner (2). Having 

 thus become available as a laboratory subject, the physiology of 

 Ochromonas has been studied by Meyers (3), Reazin (4), and Weis 

 (5). It has been found that the organism fails to grow in the light 

 unless a suitable organic substrate, such as glucose or acetate, is 

 present. This observation suggested to Meyers (3) that Ochiomonas 

 contained insufficient chlorophyll to carry out photosynthesis at a 

 rate required for growth and therefore multiplies by oxidative assimila- 

 tion of an organic substrate. The ability of Ochromonas to grow under 

 initially anaerobic conditions in the light renders this interpretation 

 less plausible. An alternative interpretation is that the light-depend- 

 ent metabolism of this alga may be in part a photoreduction, that is, 

 a bacterial type of photosynthesis. This type of photosynthesis is 

 characterized by the oxidation of an external hydrogen donor in 

 place of oxygen evolution. 



Photoreduction in algae was first observed by Gaffron (6), who 

 found that hydrogen-adapted algae in dim light fixed CO2 with the 

 simultaneous uptake of hydrogen. Frenkel (7) has extended this ob- 

 servation to a wide variety of algae. However, in the instances 

 studied photoreduction in algae was found only in resting thalli or 

 cell suspensions; growth of algae by photoreduction was not ob- 

 served. To investigate the possibility that Ochromonas might grow 

 by photoreduction, the alga was grown in the continuous culture 

 apparatus described by Benson e,t at. (8) on a synthetic medium. 

 Two types of experiments were performed: manometric determina- 



* E.xperiments were performed at the Brookhaven National Laboratory. 

 Thanks are due to Dr. M. Gibbs, in whose laboratory the work was carried out, 

 nnd to Dr. TJ. C. Fuller, whose culture apparatus \va.s use<l. 



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