Nutritional Patterns in Marine Bacterial Populations 695 



ribofla\'in, pantothenic acid and p-aminobenzoic acid are re- 

 quired by a smaller number of strains, but for none are pyridoxine, 

 pyridoxal, choline or inositol necessary. Few isolates demand 

 single vitamins for growth, the majority requiring combinations 

 of two and some of three. There is as yet no evidence of any dif- 

 ferences between bacteria from waters and from sediments in 

 respect to their specific growth factor requirements. 



No obvious relations are apparent between the morphology 

 of the various isolates and their nutritional grouping. There is 

 some evidence of a trend in which Gram-negative non-sporing 

 short motile rods are characteristic of organisms with simple re- 

 quirements while those developing in the more complex media 

 include a higher proportion of pleomorphic forms and branching 

 types possibly related to Mycoplana. Pigmentation (on mud ex- 

 tract agar) was noted less frequently among sediment isolates 

 (12-14%) than among surface and deep water forms (20-29%). 

 Organisms with inorganic requirements satisfied by sea water and 

 incapable of growth in nutrient broth prepared with demineral- 

 ised water comprised 95 per cent of the isolates from inshore 

 waters, 72 per cent from ocean waters, 66 per cent from sublittoral 

 sediments and 85 per cent from deep sediments. 



As the investigations considered here are based on material 

 obtained in one series of samplings, it is likely that repetitive 

 similar examinations of the indigenous microflora of these environ- 

 ments may reveal fluctuations in the relative incidence of the dif- 

 ferent nutritional groups of organisms. Such apparent instability 

 in the balance between constituents of microbial populations 

 would not necessarily invalidate the Lochhead method of charac- 

 terizing them, for as has been pointed out elsewhere (10), in a 

 gi\'en environment, components of the microbial populations are 

 in dynamic equilibrium with one another. Variation in this state 

 of balance may therefore be a reflection of, and indeed may in- 

 dicate the nature of, biologically influential environmental 

 changes ranging from seasonal factors to the physiological activi- 

 ties of other organisms. A more problematical question is whether 

 the nutritional idiosyncrasies of organisms determined in cultiva- 

 tion bear a real relationship to their activities pursued as mem- 

 bers of native populations. "The abundance of the \ arious groups 



