Chapter 38 



Proteolysis and Nitrate Reduction in 

 Sea Water 



Jean Brisou and Huguette Vargues 



Xhe nitrogen cycle takes place in the marine environment as 

 well as on land. Bacteria play important roles in this cycle and are 

 chiefly responsible for the processes of ammonification, nitrosa- 

 tion, nitration, denitrification and proteolysis. A great number 

 of investigations have been already made in this field. It is known 

 that the fixation of nitrogen is performed in the sea by Azoto- 

 hacteria, which are active in aerobic conditions and by Clos- 

 tridia of the pasteurianum type, which are active in anaerobic 

 conditions. Ammonification occurs as well in oxybiosis as in 

 anoxybiosis, and nitiatation is performed by Nitrobacter. Photeo- 

 lysis and the first step of denitrification, i.e., the reduction of 

 nitrate to nitrite, are performed by a great variety of aerobic 

 and anaerobic bacterial species living in sea water. The transi- 

 tion areas near the beaches and in the estuarine muds at shallow 

 depths receive continuously and abundantly materials from land 

 drainage. 



Our work is concerned with proteolysis and nitrate reduc- 

 tion in sea water and especially with the systematics of the main 

 aerobic genera and families responsible for the reactions. 



It is clear that these bacteria are not the only active ones and 

 that the anaerobes play also an important role. However, our 

 investigations have been intentionally restricted to the study of 

 the aerobic Gram negative species which are active in the con- 

 sidered processes. 



TECHNIQUES 



All the bacteria studied here (131 strains) were isolated 

 from sea water, estuarine muds, shell-fish or fishes. Some origi- 

 nated from a salt lake in the Sahara, where NaCl concentration 



410 



