Domain of the Marine Microbiologist 15 



1117 water samples from 54 stations at depths to 5370 meters 

 were examined on the Oh expedition. The number of colonies 

 developing on membrane ultrafilters through which 40 ml of 

 water had been passed ranged from nil to several hundred. 



Beginning in 1954 Soviet microbiologists (25) worked on 

 drifting ice stations in the vicinity of the North Pole (86 to QO'' 

 north latitude). Through holes cut in the ice a large number 

 of water and bottom sediment samples were collected and glass 

 slides were submerged for studying the relative abundance and 

 growth rates of microorganisms {26). Although appreciable num- 

 bers of bacteria and a few yeasts appeared on slides during twen- 

 ty-four hours submergence, some to a depth of 3450 meters, very 

 few colonies developed. 



BACTERIA IN BOTTOM SEDIMENTS 



Bacterial populations ranging from <10 tolO^ per gm wet 

 weight of bottom sediment have been detected by cultural pro- 

 cedures (61). Mean values fall within the range of 10^ to 10^ 

 bacteria per gram of sediment. Living bacteria have been dem- 

 onsti-ated at depths as great as 10,000 meters (67) and at latitudes 

 from the Equator to the North Pole ( 25 ) . Bacteria are most abun- 

 dant in the topmost layers of bottom sediments under shallow 

 organic-rich waters. The abundance of bacteria falls off fast with 

 increasing core depth. 



At many mid-Pacific Ocean stations ( depth 1700 to 5900 m ) , 

 Morita and ZoBell (40) found only 10 to 10* bacteria per gm of 

 the topmost 10 cm layer of pelagic sediment and none at the bot- 

 tom of certain cores 300 to 600 cm long. Kriss (25) reports finding 

 from 1000 to 40,000 heterotrophic bacteria per gram of surface 

 layers of sediment from deep water (2000 to 8000 m) areas of 

 tlie Okhotsk Sea adjacent to the Pacific Ocean. At the bottom 

 of cores about a meter long, bacteria were found in numbers 

 of less than 100 per gm. These low numbers may be contrasted 

 with bacterial populations of 16^ per gm of surface sediment in 

 shallow marine bays; 10"* at the bottom of 75 to 130 cm cores (41 ) . 

 In the surface layers of freshwater lake sediments Hayes and 



