74 Marine Microbiology 



oceans. Nitrosomonas and Nitrobacter are generally accepted as 

 chiefly responsible for nitrification in soil; the former oxidizes 

 ammonia to nitrite, the latter nitrite to nitrate. They obtain 

 energy for growth and CO2 fixation from the energy released by 

 the reactions. Both are considered obligate autotrophs, since they 

 cannot use organic compounds as an energy source. 



My objectives in this investigation were 1) to learn more 

 about the site of nitrification in the oceans, 2) to culture the 

 bacteria responsible for these reactions, and 3) to study the 

 physiology of these bacteria and to compare them with known 

 cultures of Nitrosomonas europaea and Nitrobacter agilis. 



METHODS AND MATERIALS 



Bottom sediments were collected in September 1957, Oc- 

 tober 1957, and January 1958 from 21 stations ranging in depth 

 from 50 to 2,000 m, off New York. Sediments were obtained by 

 means of a Phleger coring tube or a small bucket. 



Immediately after collection, 2 to 5 g of each sample were 

 inoculated into 50 ml of sterile sea water enriched with 50 /iM 

 (NH4)2S04 or 100 /xM NaNO^. The samples were returned to the 

 laboratoiy, incubated on a mechanical shaker at room tempera- 

 ture for 60 days, and analyzed periodically for nitrites and ni- 

 trates. Cultures in which 50 iM NHi'-N or 100 iM NO.-N had 

 been oxidized were scored as indicating nitrification. 



Water samples were also collected and 100 ml of each were 

 immediately dispensed in a 500-ml Erlenmeyer flask enriched 

 with 1 i-'M K..HPO4 and 50 /xM (NH4).S04. The samples were 

 incubated for 60 to 90 days on a mechanical shaker at room 

 temperature. 



On three cruises in 1959 and 1960, water samples were ob- 

 tained from the continental shelf, in slope water just off the 

 continental shelf, in the Gulf Stream, and in the Sargasso Sea. 

 Five to ten liter samples were collected by means of Van Dorn 

 bottles and enriched immediately with 50 /xM (NH,)^SO,. The 

 samples were incubated in aerated 15-liter carboys at 20 C for 

 two to four months. Periodic assays were made for nitrites and 

 nitrates. The cultures were scored as positive when nitrite or ni- 



