10 Marine Microbiology 



The seasonal variation of ocean surface temperature is gen- 

 erally less tlian 10 C, being least in tropical waters and greatest 

 in temperate zones. Below 200 meters ocean water has a nearly 

 constant temperature at any specified depth (54). At depths 

 exceeding 1000 meters temperatures are constant for large water 

 masses at between —1.5 and 4.5 C; mostly between 2 and 3 C. 

 More than 90 per cent of the marine environment by \ olume is 

 colder than 5 C. 



Besides affecting the actixity rates of organisms and possibly 

 their nutrient requirements (31), temperature is an important 

 ecologic factor. In view of the relatively low temperatures char- 

 acteristic of so much of the marine environment, one might ex- 

 pect psychrophilic microflora to predominate. Indeed, a good 

 many of the bacteria taken from the sea grow slowly in nutrient 

 media when incubated at to 5 C, but virtually all of them grow 

 much faster at 20 to 25 C. This generalization includes bacteria 

 from hundreds of samples of water and deep sea sediments taken 

 from places where the prevailing temperature is lower than 5 C. 

 Ingraham and Stokes (19) point out that bacteria capable of 

 growing slowly at C or lower are commonly found in frozen 

 foods, water, soil, and other materials, but most species of such 

 psychrotolerant bacteria grow more rapidly above 20 C. Nearly 

 half of the bacteria recently isolated from the sea will grow at 

 30 C; very few grow at 37 C or higher (62). Anomalously, how- 

 ever, a few thermophilic bacteria have been found in arctic and 

 deep sea materials. In deep ocean bottom cores Bartholomew and 

 Rittenberg (3) found from 100 to 800 bacteria per gram, which 

 developed at 60 C but failed to grow at either 20 or 37 C. In 

 arctic soil, peat, beach sand, and mud McBee and McBee (38) 

 foimd numerous bacteria which formed colonies on nutrient agar 

 incubated at 55 C. 



Apart from these anomalous thermopliilic bacteria and a 

 few thermoduric sporeformers, most marine bacteria are thejTno- 

 sensitive, generally much more so than freshwater or soil bacteria. 

 Only 7 to 18 per cent of the bacteria taken from tlie Philippine 

 Trench survived ten minutes' exposure at 40 C (62). From 20 

 to 30 per cent failed to survive ten minutes' exposure at 30 C. 

 Many of the bacteria occurring in sea water and marine mud 



