Chapter V — 69 — Distribution in the Sea 



Efifect of hydrostatic pressure: — After demonstrating the ability of 

 bacteria to tolerate a pressure of 600 atmospheres of nitrogen, Certes 

 (1884/)) concluded that the hydrostatic pressure of sea water does not in- 

 fluence the vertical distribution of microorganisms. Chlopin and Tam- 

 MANN (1903) found that bacteria, yeasts, and molds were not injured by 

 pressures as high as 2900 atmospheres. This is approximately three times 

 the greatest pressure found in the deepest part of the ocean. 



HiTE ct al. (191 4) subjected bacteria and yeasts to pressures exceeding 

 10,000 atmospheres. All of the organisms tolerated 2000 atmospheres for 

 an hour. Many were not injured by a pressure of 6000 atmospheres. 



None of the bacteria which Larsen et al. (191 8) subjected to a hydro- 

 static pressure of 3000 atmospheres were killed in 14 hours. Spore 

 formers survived at 6000 atmospheres for 14 hours, but most asporogenous 

 bacteria were killed by 6000 atmospheres. When compressed to 50 

 atmospheres, carbon dioxide killed some of the organisms. They toler- 

 ated 1 20 atmospheres of nitrogen. The sudden release of the pressure was 

 more harmful than continuous subjection to high gas or hydrostatic 

 pressure. 



Basset and Macheboeuf (1932) found that all bacteria tested with- 

 stood a pressure of 3000 to 4000 atmospheres. Some were killed at 6000 

 atmospheres. Spores of Bacillus subtilis tolerated pressures up to 17,600 

 atmospheres. Some of the bacteria examined by Basset et al. (1938) 

 resisted pressures exceeding 20,000 atmospheres, although asporogenous 

 bacteria were killed at 5000 atmospheres after 45 minutes. A pressure of 

 13,000 atmospheres was required to inactivate enzymes. 



According to the literature reviewed by Cattell (1936), single-celled 

 microorganisms tolerate pressures of 3000 to 6000 atmospheres under ordi- 

 nary conditions. Since the highest pressure in the sea approximates only 

 1000 atmospheres, it seems safe to conclude that the hydrostatic pressures 

 encountered at great depths do not restrict marine bacterial life. 



In all of the experiments upon which these conclusions are based, 

 microorganisms which normally live at a pressure of one atmosphere were 

 subjected to increased pressures. The reverse process, or a decrease in 

 hydrostatic pressure, occurs when bacteria from the deep sea are brought 

 to the surface. Finding large numbers of viable bacteria in samples of 

 bottom deposits from great depths is ample evidence that these bacteria 

 are not killed by being subjected to decreasing pressures. However, just 

 what efifects hydrostatic pressure may have on the metabolism of the 

 bacteria is problematical. 



In interpreting experiments on the effects of hydrostatic pressure on 

 bacteria, cognizance must be taken of the fact that the results are influ- 

 enced by the temperature and the composition of the medium. In some 

 of the experiments reported in the literature, the temperature of the com- 

 pressed material has approached the threshold of thermal tolerance of the 

 organisms being tested. In other experiments the products of metabolism, 

 including high concentrations of endogenous carbon dioxide, may have 

 contributed to the observed lethal effects. The rates of compression and 

 release of the pressure are likewise important factors. 



Efifect of solar radiations: — The curves in Figure 7 (p. 67) seem to 

 suggest that the abundance of bacteria in the topmost 25 to 50 meters of 

 water is more or less proportional to the intensity of sunlight at different 

 depths. A similar relationship between the abundance of bacteria and the 



