Chapter Vm — 121 — Marine Bacteria 



by ZoBell and Upham (1944) have developed the ability to grow in 

 fresh-water media. Upon initial isolation, all of them required sea water 

 or isosmotic salt solution. Interestingly, the Bacillus and Micrococcus 

 species isolated from the sea have proved to be much more curyhaline 

 than Pscudomonas or Vibrio species. Only six out of 18 species of marine 

 Pseudomonas and three out of 11 species of Vibrio became acclimatized 

 to fresh water (and these only poorly), while all of the 8 species of Bacillus 

 and all of the 6 species of Micrococcus became tolerant of fresh water. 

 Micrococcus euryhalis, M. aquivivus, M. infimus, and M. maripuniceus 

 grew equally well in either sea-water or fresh-water media after cultiva- 

 tion for a few months in the laboratory. This was also true of Sarcina 

 pelagia and S err alia marinorubra, both of which required sea water upon 

 initial isolation from the sea. 



Neither isotonic salt solution nor artificial sea water is as good as is 

 natural sea water for the cultivation of recently isolated marine bacteria. 

 Moreover, marine bacteria are as sensitive to increases in salinity as they 

 are to decreases. Our observations substantiate those of Korinek (1926) 

 that marine bacteria are even less resistant than are fresh-water bacteria 

 to changes in osmotic pressure. 



Doubling the salinity of sea water either by the addition of NaCl or 

 sea salt may reduce by 25 to 50 per cent the number of marine bacteria 

 which will grow in it. Very few marine bacteria have been observed to 

 grow in sea- water media to which 12 per cent NaCl has been added. 

 Thus, while marine bacteria are often characterized as being halophilic or 

 salt-requiring, they are far less so than are bacteria found in salted fish, 

 salt-cured furs, pickle brines, salt lakes, and limans (see Chapter XVIII). 

 Virtually no marine bacteria, exclusive of those found in salterns or asso- 

 ciated with salted fish or similar marine products, grow in sea water to 

 which 24 per cent NaCl has been added. Numerous bacteria which occur 

 in strong brines flourish in media containing from 18 to 30 per cent NaCl 

 (HoF, 1935). 



Studies on their salinity requirements indicate that, while bacteria 

 from different environments differ in salt tolerance and in their ability to 

 become acclimatized to changes in osmotic pressure, most of the bacteria 

 found in the sea, exclusive of adventitious contaminants, are specifically 

 marine. This conclusion is substantiated by the fact that very few com- 

 monly known species of terrestrial bacteria such as members of the coli- 

 form, subtilis-mesentericus , or Gram-positive cocci groups have been found 

 in the sea except relatively near land. 



Temperature tolerance : — Forster (1892), Drew (1914), Angst (1929), 

 and others have emphasized the extreme thermal sensitivity of marine 

 bacteria. Berkeley (1919) believed that low plate counts obtained with 

 sea water collected from depths of 20 to 100 fathoms may be due to the 

 failure of some of the bacteria to tolerate the plating temperature of 

 nutrient agar, i.e., about 42° C. Lloyd (1930) suggested using plating 

 temperatures ranging from 25° to 35° C. to avoid killing "ordinary micro- 

 organisms" indigenous to the sea. 



The data in Table X on page 46 show that if plating temperatures of 

 the medium exceed 42° C. by a few degrees, plate counts on samples of sea 

 water and marine mud are noticeably decreased. These studies were ex- 

 tended by ZoBell and Conn (1940) with the use of nutrient gelatin, 

 which soHdifies at lower temperatures than does agar. The data in Table 



