Domain of the Marine Microbiologist 5 



quire sea water or its equivalent. Most recently isolated species 

 grow almost equally well at any salinity between 20 and 40 per 

 cent. Fewer than half of such species grow well in nutrient 

 media prepared with double strength sea water {S%o = 70) or 

 in media prepared with sea water diluted with distilled water 

 to reduce the salinity to 10 '}{c. In general, marine microorganisms 

 tolerate hypotonicity much better than hypertonicity. Their 

 tolerance increases during laboratory cultivation. Tlie propor- 

 tion of sodium, potassium, calcium, magnesium, and other 

 major ions as well as the salinity and osmotic pressure of the 

 milieu influence the growth and metabolism of marine bacteria 

 (35, 36, 55). 



Although there is some variation in the salinity of water 

 in the open ocean, the ratios between the major ions are virtually 

 constant. Tremendous differences in these ratios occur in differ- 

 ent fresh, brackish, and superhaline waters depending upon the 

 source and history of the water. The ratios of the principal anions 

 (carbonates: chlorides: sulfate) and cations (calcium: magnes- 

 ium: sodium: potassium) in sea water are quite different from 

 these ratios in most fresh waters (Table 1). The ratios of most 

 brackish waters are intermediate between those of fresh water 

 and sea water. Evaporation of sea water results in marked changes 

 in the proportions of ions owing to differential precipitation of 

 salts. 



TABLE 1 



Average R.\tios of M.'^jor Ions in Ocean Water Compared with the 



Mean Values for Many River Waters and Some Soft Water Wisconsin 



Lakes, Computed From Data of Clarke (7) and Hutchinson (18) 



* Including HCO3' where present 



