ZoBell — 138 — Marine Microbiology 



penetrated by light. In oceans as well as in lakes there is much more 

 ''dissolved" organic matter than particulate (including plants and ani- 

 mals). 



The so-called ''dissolved" organic matter represents that which is not 

 removed with a high speed centrifuge. It includes minute particles of de- 

 composing organic material, some bacteria, colloids, and organic matter in 

 true solution. Although some of the colloidal and minutely particulate 

 organic matter can be assimilated by certain filter-feeding and mud- 

 eating animals, most of it and all of that in true solution can be utilized 

 only by bacteria and allied microorganisms. Juday (1942) points out 

 that "the dissolved organic matter is in a constant state of flux; it is con- 

 tinually receiving both decomposing and excretory materials from the 

 biota on the one hand and losing organic substances that change over to 

 inorganic compounds on the other." 



After noting marked increases in the bacterial population and oxygen 

 consumption in filtered sea water incubated in the laboratory, Waksman 

 and Carey (1935a) concluded that sea water contains sufficient organic 

 matter in true solution to support an extensive bacterial population under 

 favorable conditions. In the decomposition of the organic matter in sea 

 water by bacteria, a definite parallelism was obtained between bacterial 

 multiplication, oxygen consumption, and liberation of nitrogen as 

 ammonia. 



When sea water was placed in glass containers and kept under favor- 

 able conditions, Waksman and Carey (19356) found that from 25 to 

 50 per cent of the organic matter was decomposed within 10 or 12 days, 

 as measured by the amount of oxygen consumed and ammonia liberated. 

 About 60 per cent of the organic matter decomposed was completely 

 oxidized, as shown by the amount of oxygen consumed, and about 

 40 per cent of it was converted into bacterial cell substance and other 

 products of bacterial metabolism. The rapidity of the process was found 

 to be influenced by the temperature, oxygen tension, abundance of or- 

 ganic matter, and the chemical nature of the organic substrate itself. 



After five or six months storage in the dark the organic content of 

 filtered sea water was found by ZoBell and Grant (1943) to be reduced 

 to around 0.2 mgm./L. from an original 3 to 4 mgm./L. Glucose, glycerol, 

 ethanol, lactate, succinate, starch, and asparagine in concentrations rang- 

 ing from 0.25 to 5 mgm./L. were quantitatively utilized by bacteria in sea 

 water in from 16 to 30 days at 22° C. From 60 to 70 per cent of the or- 

 ganic substrate is oxidized and 30 to 40 per cent is converted into bac- 

 terial protoplasm and intermediate products. Cultures attack concen- 

 trations of glucose as low as o.i mgm./L. 



While the chief function of bacteria in the transformation of organic 

 matter appears to be the utilization of "dissolved" organic matter, there 

 is an extensive bacterial flora in the sea which is uniquely adapted to de- 

 compose chitin, lignin, waxes, cellulose, and other complex organic sub- 

 stances which are assimilated poorly, if at all, by other types of organisms. 



Decomposition of carbohydrates : — Simple sugars ranging from trioses 

 to hexoses are readily assimilated by many species of marine bacteria. 

 In a balanced mineral solution containing an available source of nitrogen, 

 simple sugars are quantitatively utilized. Part of the carbon is oxidized 

 to CO2 as a source of energy and part is converted into bacterial proto- 

 plasm. The quantitative oxidation of glucose by bacteria in sea water 



