694 Marine Microbiology 



of organisms. Although there is much circumstantial evidence that 

 certain auxotrophic algae and flagellates are ultimately depend- 

 ent in the sea upon products of bacterial metabolism (cf., 18), a 

 great deal more information is required to evaluate relations be- 

 tween bacteria and marine algae. A notable observation was Col- 

 lier's (3) record of a persistent association in culture between 

 the dinoflagellate, Gijmnodinium hreve, a vitamin B12 auxotroph, 

 and a dominant type of bacterium found to be a B12 producer. 

 It was suggested that the alga may have supplied a substrate 

 utilized, perhaps preferentially, by the bacterium. These consider- 

 ations indicate that further studies of the nutritional requirements 

 and biosynthetic potentialities of marine bacteria may be usefully 

 supplemented with appropriately selected syntrophic experiments 

 with unicellular algae and protozoa. 



Sediment bacteria which showed maximum growth only in 

 the medium supplemented with marine mud extract have not 

 yet been investigated as a group. As slight or submaximal growth 

 in most cases occurred in other media, it is unlikely that the 

 marine mud extracts supplied any imknown growth factors, 

 neither can these isolates be regarded as necessarily having com- 

 plex growth requirements, for the extracts could well have sup- 

 plied simple non-amino carbon or energy sources other than 

 glucose that were unavailable in other media. It is noteworthy 

 that all agar-digesting forms, which comprised some 2 per cent 

 of strains isolated from surface inshore waters, developed pre- 

 ferentially in the yeast mud extract medium. Although extracts 

 may contain humic constituents that serve as metal chelators, 

 their effects in this respect cannot yet be assessed. Some of the 

 marine mud extracts that have been prepared have been found 

 to be inhibitory to certain isolates - a variable that may militate 

 against their value in isolation media. 



For important proportions of the strains isolated from sedi- 

 ments, oceanic surface and deep waters, vitamins were essential 

 for growth. Preliminary studies indicate that tlie specific vitamins 

 most frequently required bv these isolates are, in order, thiamin, 

 biotin and cyanocobalamin; these, coincidentally, are listed as the 

 three most important vitamins in the ecology of auxotrophic 

 marine algae and flagellates (18). Folic acid, nicotinic acid, 



