148 



Marine Microbiology 



N43 MY36 

 A 



MY36 



P85 

 B 



N35 



Fig. 6. Exchange of certain B vitamins synthesized by matched auxotrophs 

 allows growth of bacteria, within the areas of mutual influence, in agar 

 media where the required vitamins had been omitted. A, culture My36 B;- 

 Panto^exchanges with culture N43 B;"^ Panto-, with resulting mutual bene- 

 fit. B, culture P85 Nicotinic acid+B2+ contributes these vitamins to cultures 

 N35 Nicotinic acid- and My36 B^-. 



Other metliods of demonstrating exchange of B vitamins 

 have been used with hquid media. Complementary types of 

 vitamin-deficient bacteria are inoculated singly and as mixtures, 

 into suitable media lacking the required vitamins. Thus, cuhure 

 238 requiring thiamine and culture 507 requiring biotin v^^ere 

 alone unable to grow well in a medium lacking both of these 

 vitamins; in mixed culture, however, good growth was observed. 

 Two vitamin Bi-deficient cultures served as an example for 

 exchange of intermediates in syntrophic mixed culture. Culture 

 276 required pyrimidine, and culture 776 required thiazole. Alone, 

 neither culture was able to grow well in a medium lacking vita- 

 mins; together they apparently exchanged the thiazole produced 

 by culture 276 and the pyrimidine fonned by culture 776, and 

 both grew well in a medium that was initially without thiamine. 



CONCLUSIONS 



1. Among the auxotrophic algae and bacteria of shallow 



