BACTERIA IN THE DEEP SEA 207 



metre of deep-sea bottom; perhaps ten times this weight of bacteria live 

 there. Large numbers of Hving bacteria were also demonstrated in water 

 samples taken just off the bottom of the abyssal deeps investigated by the 

 Galathea. 



Although from 0.0002 to 0.02 grams of bacteria per square metre of 

 ocean floor may be considered a small "standing crop" as compared with 

 the crops harvested from fertile garden soil, this amount compares favourably 

 with the total weight of animals found by zoologists on the Galathea Expe- 

 dition. Since the bacteria grow rapidly and have a short generation time, 

 they may produce several "crops" each year. How rapidly they grow or 

 reproduce on the deep-sea floor is problematical, but in the laboratory it 

 has been shown that bacteria reproduce every few hours in nutrient sea- 

 water medium held at the same pressure and temperature that prevail 

 on the sea floor. 



Bacteria reproduce by simple fission, the parent cell dividing to form 

 two daughter cells. Under favourable conditions, the daughter cells reach 

 maturity within two to twenty hours, during which time they reproduce 

 by dividing to form four new cells. The resultant four give rise to eight, 

 eight to 16,, 16 to 32, 32 to 64, etc., assuming there is no mortality and 

 all progeny find conditions favourable for growth and reproduction. 



Obviously, not all of the bacteria in the ocean find conditions suitable 

 for reproduction and many more never live long enough to reproduce. 

 Perhaps the principal cause of bacterial mortality is the predatory animals 

 which feed upon bacteria in much the same way that cattle or sheep 

 graze the grass from pasture lands. The grazing cattle or sheep may leave 



Micro-photograph of a 

 culture of barophilic 

 bacteria from the Ker- 

 madec Trench. They 

 have been provisionally 

 named Bathycoccus 

 galathea. Aiagnified 

 about 3,500 times. 



