Marine Bacteriolooy and the Problem of Mineralization 51 



qiience of appearance of these molecules in situ, as for example 

 in the English Channel (5), it was not difficult to accept that 

 the nitrogen cycle in the oceans is essentially the same as that 

 on land. 



As knowledge of the potential role of bacteria in the oceans 

 increased, attempts were made to explain oceanographic phe- 

 nomena in terms of bacterial processes. The most prominent early 

 attempt was that of Brandt (2) who attributed the low pro- 

 ductivity of tropical seas to the release of molecular nitrogen by 

 denitrifying bacteria. The hypothesis was supported by the ease 

 with which bacteria, that denitrified under laboratory conditions, 

 could be isolated from sea water. This hypothesis led to a very 

 active controversy and ultimately to the rejection of the idea on 

 two main grounds; Gran's (10) conclusion that denitrifying 

 organisms do not use nitrate if oxygen is axailable (which is in 

 accord with modern findings), and the insufficiency of organic 

 matter in the water to provide for the activity of these organisms 

 (32 p. 155). It is important to point out here that no attempts 

 were made until very recently, to demonstrate denitrification in 

 situ which, of course, gets at the crux of the problem. 



The situation is comparable in much of the work concerned 

 with mineralization in the marine environment. Investigators 

 have been content to demonstrate a potential organism for a 

 process or the process itself in laboratory experiments under 

 artificial conditions and then extrapolate the results to the oceans. 

 Unfortunately, with enough effort, almost any kind of bacterium 

 can be isolated from marine sediments and even from sea water 

 itself, but this is not enough to demonstrate the significance of 

 the process catalyzed by the bacterium. What is lacking in gen- 

 eral, is both the demonstration of the process in situ and the 

 quantitative assessment of its significance. 



The laboratory approach has sometimes led to oceanograph- 

 ically unintelligible results, as in the case of nitrification. Enrich- 

 ment cultures inoculated with sea water generally fail to nitrifv, 

 whereas those inoculated with marine sediments usuallv do 

 (26, 3, 32 p. 151-153). However, the physio-chemical nature of 

 the two environments, as well as the distribution of ammonia, 

 nitrite and nitrate in the oceans, suggest that the water is the 



