Autotrophic Nitrification in the Ocean 81 



regions, probably the alpha and beta peaks of cytochrome c 

 (Fig. 3). 



Marine and terrestrial bacteria that oxidized ammonia re- 

 sponded almost identically to varying concentrations of ammonia. 

 Maximum growth rates were obtained for botli in media con- 

 taining 25 - 100 mM (NH4)jSOi. Maximum respiration rates were 

 constant for both over a range of ammonia concentrations of 

 2 - 250 mM. Abo\ e 250 mM the rate decreased rapidly and in a 1 

 M solution oxygen uptake decreased by 80 per cent. 



Optimal pH for respiration for Nitrosomonas europaea and 

 its marine counterpart varied with the ammonia concentration. 

 In the marine culture, maximum oxvgen was consumed between 

 pH 7.0 and 8.1 when the (NH4)-SOi concentration was 2.5 mM, 

 and between 7.0 and 7.5 at 310 mM (Fig. 4). Nitrosomonas 



Fig. 4. The effect of hydrogen ion concentration on the respiration of am- 

 monia-oxidizing bacteria. 



