SOURCES OF ENERGY IX AXAEROBIOSIS 195 



In most cases, the evidence presented to show that pro- 

 teins serve as a source of energy under anoxic conditions 

 is not too reliable. Piitter (1905) pointed out that speci- 

 mens of Paramaecium that had stored but little glyco- 

 gen survived for long periods in the absence of oxygen, 

 and Lauterborn (1916) observed that the ctenostomids, 

 t}i)ical sapropelic ciliates, do not store any glycogen at 

 all. Both these authors assume that proteins may fur- 

 nish the necessary energ}^ to sustain life. This problem 

 needs to be reinvestigated, however, since Liebmann 

 (1936) pointed out that a quite different mechanism may 

 be involved. According to him the anaerobic survival of 

 Colpidium colpoda depends upon the ability of this cil- 

 iate to engulf green sulfur bacteria. A temporary sym- 

 biosis is then established and the ciliates participate in 

 the energy produced by the assimilative function of the 

 bacteria. 



A similar mechanism may be widespread among cer- 

 tain groups of ciliates. Liebmann (1937, 1938) found 

 some undetermmed bacteria regularly associated with 

 sapropelic ciliates and his experiments indicate strongly 

 that it is only these bacteria that enable the ciliates to 

 survive in their normally oxygen-free habitat. They live 

 at first as symbionts in vacuoles or they are embedded 

 directly in the protoplasm. From time to time they gath- 

 er in food vacuoles and are digested. If the supply of 

 these specific bacteria fail the ciliates die, despite the 

 abundance of other food. Liebmann 's (1937, 1938) ten- 

 tative assumption that the bacteria liberate oxygen from 

 some undetermined source and supply the ciliates with 

 it lacks experimental proof as yet. To this assumption 

 one may also object that the ciliates should be able to 

 survive without bacteria in media containing oxygen, if 

 only the hypothetically produced oxygen maintains them 

 in otherwise anaerobic media. As mentioned previously, 



