32 THE METABOLISM OF ALGAE 



TABLE 3 



ALGAE WHICH HAVE BEEX TESTED FOR ABILITY TO CARRY OUT 



PHOTOREDUCTION ^"^ 



Class Species successfully Species not showing 



adapted photoreduction 



Chlorophyceae . ScenedestJiiis obliqiius Chlorclla pyrenoidosa 



Arikistrodesffius sp. 



Chlamydomonas moeuusii 



Ulva lactuca 

 Bacillariophyceae — Nitzschia spp. 



Phaeophyceae . Ascophyllum nodosum — 



Rhodophyceae . Porphyra lonbilicalis — 



Porphyridiinn criientiim 

 M>'xophyceae . Synechococcus elofigatus Oscillatoria sp. 



Synechocystis sp. Nostoc ynuscorum 



Cylindrospermum sp. 



This type of photosynthesis probably does not occur to 

 any great extent in algae under natural conditions. After 

 carrying out the reaction for several days certain algae have 

 been found to have shown no multiplication or increase in 

 chlorophyll concentration comparable to that caused by a 

 similar period of normal photosynthesis. ^^'^ It is, however, 

 generally found that green algae do not grow under anaero- 

 bic conditions. There is some evidence that the products of 

 photosynthesis using elementary hydrogen are similar to 

 those of normal photosynthesis^^' ^^^ and there is no reason 

 to suppose that they are inherently unsuitable as substrates 

 for growth. Porphyridium, a red alga, has been found to 

 increase in dry w^eight and pigmentation while carrying on 

 photosynthesis using elementary hydrogen under anaerobic 

 conditions. ^^^ 



A blue-green alga, Oscillatoria, and a diatom, Pinnularia, 

 have been reported as able to use hydrogen sulphide, which 

 is actually an inhibitor of photosynthesis in higher plants, as 

 hydrogen donor. -^^' ^^^ The evolution of oxygen is here 

 replaced by the deposition of sulphur within the cells and 

 the prq^s is thus apparently similar to that in the green 

 sulphu^acteria, represented in equation 3: 



COo+2HoS->(CHoO)+H20+2S . . (3) 



Hydrogen-adapted Synechococcus and Scenedesmus have 

 also been found to be able to utilize hydrogen sulphide as a 



