LIFEINGREATDEPTHS 163 



the Philippine Trench at a depth of 10,400 meters the 

 bacteria cultivated at a pressure of 1,000 atmospheres 

 were a thousand times more numerous than in cultures 

 under one atmosphere. Other experiments made with 

 bacteria from relatively shallow water prove that they 

 do not grow at the high pressures characteristic of 

 extremely deep water. Obviously the bacteria found in 

 deep-sea mud must be species indigenous to the deep 

 sea.^ 



It is well known that most of the organic matter in the 

 sea is produced by photosynthesis in the euphotic zone, 

 that is, in the topmost few hundred meters of water. 

 How much of this organic matter reaches the deep-sea 

 floor is problematical. The low organic content of many 

 deep-sea bottom deposits suggests that a relatively 

 small amount of organic remains reaches abyssal 

 depths. What then is the source of food for deep-sea 

 organisms? ZoBell, in 1946, suggested that the organic 

 matter in oceanic depths is supplemented to a signifi- 

 cant extent by bacteria, which are known to serve as a 

 source of food for many types of marine animals. 

 Heterotrophic bacteria synthesize cell substance by 

 utilizing dissolved and other suspended organic matter, 

 commonly found in sea water in amounts of about 5 

 milligrams per liter. 



By their assimilation of dissolved, colloidal, detrital, 

 or other forms of organic matter and conversion of 

 30% to 40% of it into nutritious cell substance, bac- 

 teria may serve as an important source of organic 



