46 Marine Microbiology 



which it was hoped might serve as an indicator group to study 

 the loci of nutrient cycles in the sea. Chitin-destroying bacteria 

 are very rare in sea water but occur attached to zooplankton or- 

 ganisms; thus it appears that the bacterial cycling occurs on the 

 bodies of individual organisms, from wliich the nutrients are 

 directly released to the water. The zones or layers of bacterial 

 decomposition thus correspond roughly with the places of zoo- 

 plankton abundance. The gut contents of certain fishes were found 

 to contain populations of chitin-destroying bacteria, as might 

 be expected if these fish are feeding on zooplankton. 



In its final portion the meeting heard three reports on spe- 

 cialized problems of distribution. Liston and Colwell (Chapter 

 57) have investigated the question of whether bacterial popula- 

 tions were specifically associated with marine animals, i.e., does 

 the species of marine animal and its environment determine 

 which bacteria are present? Swab samples were taken from fish or 

 invertebrates for culturing. Collections from both north and south 

 Pacific showed Pseudomonas and Achromohacter types to be of 

 overwhelming importance, the two together accounting for over 

 half of the total flora. Species of microorganisms having similar 

 physiological characteristics tended to predominate in each j)ar- 

 ticular environment provided by the body of tlie host animal. 

 Bacteria from vertebrates tended to be more active biochemical- 

 ly than those from invertebrates. There was on the whole little 

 evidence of any taxonomic difference between the bacterial pop- 

 ulations of vertebrates and invertebrates, or among populations 

 derived from different geographical areas. However, bacteria did 

 exhibit the adaptation which has been described for higher or- 

 ganisms, of being acclimated to the temperature of their environ- 

 ment. 



The cycling of microorganisms in Arctic seas was described 

 by Bursa (Chapter 58), who has repeatedly observed a spring 

 maximum of Pennatae under the April ice, followed in August by 

 the characteristic summer Centriceae and often dinoflagellates. 



In the final paper of the session, Pratt and Austin (Chapter 

 59) described the effect on growth rate of microorganisms by di- 

 lution of sea water, and of substitution of ions, such as might be 

 found in estuarial and other situations. Sulphate was found to be 



