Some Nutritional Relationships Among Microbes 137 



group, it is important to inquire into the origins and availability 

 of these substances in the marine environment. 



PRODUCTION AND OCCURRENCE 

 OF B VITAMINS IN MARINE ORGANISMS 



Earlier studies have indicated the widespread occurrence of 

 B vitamins in marine muds ( 2 ) , algae, and ocean waters ( 8, 13 ) . 

 The concept that some of the B vitamins arise by biosynthesis in 

 the marine environment has been supported by various investi- 

 gations. As a basis for studies of vitamin exchanges among marine 

 microorganisms, further determinations have been made for pro- 

 duction of the four B vitamins required most frequently by auxo- 

 trophic marine algae and bacteria. 



For our present studies of vitamin production, two methods 

 were employed: crude enrichment cultures, and pure cultures of 

 bacteria in a chemically defined medium. Following a suitable 

 period of growth, the samples of broth cultures were prepared for 

 assays in accordance with simple modifications of standard meth- 

 ods (1). Microbiological tests for the B vitamins were performed 

 in poured plates seeded with suspensions of vitamin-requiring 

 bacteria selected out of our screening program. The basal assay 

 medium is indicated in Table 1. Supplements of appropriate 

 vitamins were added to the medium as required, so that growth 

 of the assay organisms would indicate the amount of a vitamin 

 in standard solutions or in crude bacterial culture broths applied 

 in one-half inch paper discs to the surface of the seeded agar 

 test plates. Calculations of vitamin potency of unknowns could 

 be made by reference to standard curves obtained in tliese plate 

 assays. 



Growth and vitamin production of marine bacteria in crude 

 cultures of enriched marine muds were studied in flasks contain- 

 ing sea water, phosphate, and organic sources of carbon and ni- 

 trogen. The numbers of bacteria were determined at the begin- 

 ning and after three days, by the dilution method, and vitamins 

 were assayed with the standard agar plate technique. As the 

 numbers of bacteria increased, so also did the amounts of the 

 four important B vitamins. 



Production of vitamins was determined in pure cultures of 



