[BERKELEY] MARINE BACTERIA 27 



In addition to the fact that no bacteria capable of bringing about 

 denitrification are demonstrable in the samples under examination 

 the following conclusions can be drawn from these results: — 



(i) The surface water contains bacteria capable of reducing 

 nitrate to nitrite and nitrite to ammonia. In the absence of 

 peptone the latter reaction does not set in at 28°C for 22 days 

 and at air temperature only after 3 months. In the presence of 

 peptone ammonia is formed immediately, but this is probably 

 independent of the formation of nitrite and is due to the direct 

 action of other bacteria on the peptone. 



(ii) No bacteria contained in the 20 fathom and 100 fathom 

 samples will grow in the media under consideration at 28°C. 



(iii) The 20 fathom sample when inoculated into media kept 

 at air temperature behaves in the same way as the surface sample 

 in respect of nitrite and ammonia formation except that nitrite 

 formation does not set in so rapidly in the presence of peptone 

 and ammonia is not formed even after three months in its absence. 



(iv) The 100 fathom sample when inoculated into media kept 

 at air temperature grows freely but does not form nitrites (the 

 reaction after 6 days in the absence of peptone seems to be an 

 anomaly). It forms ammonia freely in the presence of peptone. 

 Whenever growth took place these cultures were plated on medium 

 A. Colonies of the following types were obtained in this way 

 and subcultures made from each type on to a slope of the same 

 medium : — 



(i) Round, white, flat, dry and adhesive to medium, undulate 

 edge, rough surface (Culture XVII). 



(ii) Round, white, flat, moist, entire edge, smooth surface 

 (Culture XVIII). 



(iii) Small, round, white, raised, entire edge, granular surface 

 (Culture XIX). 



(iv) Smooth, yellowish, flat, round, entire edge, finely granular 

 surface (Culture XXVII). 



These were all obtained from the cultures inoculated with surface 

 water. No satisfactory development of colonies was obtained on the 

 plates from the cultures inoculated with the 20 fathom and 100 fathom 

 samples probably for the reason suggested in the footnote on p. 21. 



The Precipitation of Calcium Carbonate. 



In all the cultures in the denitrification media bacterial growth 

 was accompanied by the formation of a white precipitate clearly 

 distinguishable from the growth itself. Culture of the organisms 



