ZoBell — 120 — Marine Microbiology 



plated on media prepared with fresh water rather than with sea water. 

 Diluting sea water by 50 per cent reduces both its growth-promoting 

 properties for marine microflora and its toxicity for terrestrial bacteria, as 

 shown by the data in Table XXXII on page 119. 



Similar results have been reported by Berkeley (1919), Korinek 

 (1926), LiPMAN (1926), and others. Korinek (1927) believes that marine 

 bacteria can be distinguished from non-marine forms upon a basis of their 

 salt tolerance. While this may not be true of every individual culture, 

 it is statistically true of marine bacteria as a group. The effect of the 

 dilution of sea water is shown by the following data which Lipman (1926) 

 obtained by plating sea water collected one mile from land on sea-water 

 media diluted with distilled water : 



As shown below, Lipman obtained somewhat different results when he 

 plated sea water collected from the wharf at the Tortugas Laboratory 

 where there was much shore contamination : 



The beneficial effects of sea water on marine bacteria and its inhib- 

 itory effects on non-marine bacteria are most conspicuous when appro- 

 priately diluted samples of marine or non-marine materials are plated on 

 media containing different concentrations of sea water. This is illustrated 

 by the experiments described above. Following laboratory cultivation, 

 many bacteria seem to develop a tolerance for certain types of adverse 

 conditions. As a matter of fact, most old stock cultures of either marine 

 or non-marine bacteria will grow almost equally well on either sea-water or 

 fresh-water media when the media receive large inoculations. However, 

 marked differences are noted in the salt tolerance of individual cells con- 

 stituting the respective cultures if they are properly diluted and then 

 plated on the two kinds of media. Under these conditions there emerge 

 statistically determined preferences of marine bacteria for sea water and 

 of the non-marine bacteria for fresh water. Within old stock cultures, 

 though, some individual cells are found to be euryhaline over a wide range 

 and others are relatively stenohaline. The salt requirements of the latter 

 may be high, low, or intermediate, depending upon the origin and cultural 

 history of the organism. 



According to Korinek (1927), after a year's cultivation original differ- 

 ences in the salinity requirements between fresh-water and marine bac- 

 teria were not eliminated. Conversely, 9 of 12 cultures isolated from the 

 sea and maintained in the laboratory for five months by ZoBell and 

 Michener (1938) were able to grow in fresh-water media, although upon 

 initial isolation they required sea-water media. The conditions under 

 which the organisms are cultivated unquestionably influence the results. 



After laboratory cultivation on sea-water media for periods of from 

 two to twelve years, 56 of the 60 new species of marine bacteria described 



