418 



Marine Microbiology 



TIME (days)-* 



Fig. 1. Nitrification by organisms in sediment samples from the Bay of 

 Algiers. Ammonia is provided by Omeliansky medium. 



were inoculated in 100 ml Omeliansky 's medium. In these curves 

 arbitrary time is expressed on the abcissa, and the weight of 

 nitrous or nitric N in micrograms per 10 ml of culture medium on 

 the ordinate. 



The average of these curves is reproduced in Figure 1, for 

 samples taken at a depth of 63 m in the bay of Algiers. The ni- 

 trite curve is bell-shaped, diminishing rapidly when maximum 

 production is reached, i.e., when ammonium nitrogen is ex- 

 hausted. Simultaneously, the nitrate curve starts and has a sig- 

 moidal aspect. But has to be stressed that if the curve was pro- 

 longed in time, a decrease in the percentage of nitrates would be 

 observed, corresponding to the phenomenon of de-nitrification. 



The nitrite and nitrate produced in the culture medium 

 provide curves similar to bacterial growth curves, showing a lag 

 phase, a period of rapid growth, a stationary phase, and a phase 

 of regression; this last phase being faster in the present case, 

 due to the fact that a second process utilizes the metabolic pro- 

 ducts of the first. 



INTERPRETATION OF CURVES 



Nitrite Production 



The lag phase has a minimum duration of two days and a 

 maximum duration of twenty days. According to the variation 



