Some Nutritional Relationships Among Microbes 147 



common "laboratory" strains. Certainly antibiosis must have con- 

 siderable ecological significance in the oceans (3, 11). 



EXCHANGES OF VITAMINS 

 AMONG GROWING MICROORGANISMS 



In order to show that actual vitamin exchanges take place 

 simultaneously between different kinds of microorganisms, 

 special experiments have been devised with cultures possessing 

 recognizable characteristics. Several examples will be given to 

 illustrate the principle of metabolite exchange in the phenomenon 

 of syntrophism. 



For the purpose of demonstrating the contribution of vitamin 

 Bi2 by bacteria to the blue-green alga Synechocystis, seeded plates 

 of the latter were prepared, with ASP-2 medium and 1.0 per cent 

 purified agar, poured into sterile plastic petri dishes. In some 

 experiments, this medium was supplemented with Difco vitamin- 

 free Casamino acids 0.5 per cent, dextrose 0.2 per cent, and 

 sodium succinate 0.2 per cent, in order to encourage more rapid 

 growth of bacteria. Bacterial cultures, known to produce vitamin 

 Bi2, were impregnated in paper discs and placed on the algal- 

 seeded plates, or the bacteria were inoculated directly on the 

 surface of the agar seeded with Bi.-requiring Synechocystis. 

 After several days of incubation in an atmosphere of air and 1% 

 CO2 at 28 C in a light room, zones of the blue-green algae grow- 

 ing in ASP-2 medium became evident around the pads contain- 

 ing bacteria that produce vitamin B12. In the other plates con- 

 taining organic additions, where the inoculated bacteria grew 

 and produced B12, there developed excellent growth of the blue- 

 green algae intermingled with the feeder bacteria. 



Effects of excreted vitamins have been demonstrated be- 

 tween a bacterium that produces large amounts of man\' B vita- 

 mins and other bacteria requiring riboflavin and nicotinic acid 

 (Fig. 6). Also the simultaneous exchange of riboflavin for 

 pantothenate has been observed between cultures My36 and N43, 

 growing in an agar plate lacking these required vitamins. If 

 simultaneous import and export of vitamins did not take place in 

 a vitaminless environment, no growth of such deficient cultures 

 could occur. 



