ZoBell — 32 — Marine Microbiology 



faces which were exposed to the water. Brightly polished metals are 

 known to be more bacteriostatic than those which are coated with oxides 

 or other film-forming substances. 



Not only does contact with brass and similar copper-containing alloys 

 tend to decrease the viable bacterial population in sea water; the sea 

 water itself is rendered less growth-supporting by contact with copper, 

 lead, nickel, silver, tin, or zinc. Sea water is affected more than fresh 

 water by such metals. It is recommended that sea water which is to be 

 used for the cultivation of microorganisms be collected and stored in glass, 

 ceramic, or other non-metallic containers. Diatoms are more sensitive 

 to traces of heavy metals than are some of the bacteria. 



Effect of pressure during sampling : — The hydrostatic pressure of 

 sea water increases with depth by approximately 15 pounds per square 

 inch for each 10 meters. This is enough to force the rubber stopper into 

 a test tube at a depth of 20 to 30 meters. If the test tube is not broken at 

 100 meters, the rubber stopper will be pushed half way to the bottom of 

 the tube. This difficulty can be obviated by using test tubes or bottles 

 with constricted necks to prevent the descent of the rubber stopper. Con- 

 stricting the neck to half the diameter of the bottom end of the stopper 

 provided for a perfectly water-tight seal at all depths tolerated by ordi- 

 nary laboratory glassware. The same result can be achieved by placing a 

 piece of thick-walled glass tubing in citrate of magnesia bottles so that the 

 upper end of the vertical tube contacts the inserted end of the rubber 

 stopper. 



Citrate of magnesia bottles, which are commonly used by hydrogra- 

 phers for storing water samples, were found to be pressure-resistant to a 

 depth of 100 meters. In one series of experiments, 120 rubber-stoppered 

 citrate of magnesia bottles fitted with thick-walled glass tubes to prevent 

 the descent of the stoppers were immersed by tying them to the weighted 

 hydrographic cable. They all came up intact and empty after being low- 

 ered to 100 meters. When lowered to 200 meters, 8 of the bottles were 

 broken by the pressure. Eighty-four of the bottles came up intact after 

 being lowered to 300 meters. Only 32 of the original 120 bottles tolerated 

 the pressure encountered by being lowered to 400 meters and none of them 

 survived pressures at 600 meters. 



Little is known concerning the effect of hydrostatic pressure on the 

 viability and physiological activities of microorganisms. The fact that 

 large numbers of viable bacteria have been found in bottom deposits col- 

 lected from depths exceeding 5000 meters shows that these bacteria can 

 live at high pressures and that many of them are not injured by the release 

 of the pressure effected by bringing the mud samples to the surface. 



It is still questionable whether some bacteria are injured by the sudden 

 change of pressure when samples are collected with an evacuated glass 

 bulb. When the capillary tube on such a sampler is broken in water one 

 mile deep, the pressure of the inflowing water changes almost instantane- 

 ously from nearly a ton per square inch to near zero. Gee (1932a) made 

 provisions for minimizing the deleterious effect this might have on the 

 microbes in the water by extending the capillary tube to a length of 

 20 inches. He explains that the long capillary tube "acts as a spring, 

 preventing hammering action of the inrushing water." 



Although one might expect the sudden release of pressure to be in- 

 jurious to microorganisms in the water, there is no evidence to prove it. 



