Vallentyne: Environmental Biophysics & Microbial Ubiquity 349 



(2) Bacteria that grow actively in solutions containing 1 g. of phenol per 

 liter (Putilina, 1959). 



(3) Growth of the fungus Aspergillus in a 40 per cent solution of citric acid 

 (Johnson, 1923). 



(4) An aerobic bacterium (Hydrogenomonas?) , originally isolated from sewage 

 sludge that shows poor growth in air, but develops well in an atmosphere con- 

 taining 20 per cent by volume O2 and 80 per cent by volume CO (Kistner, 1953). 



(5) Heterotrophic growth of algae in lakes during the sunless arctic winter 

 (Rhodhe, 1955) and reproduction of algae in subterranean caves (Claus, 1955). 



(6) The survival of some bacterial spores after 5 hours' immersion in non- 

 aqueous media at temperatures approaching 140° C. (Rodenbeck, 1932). 



(7) The survival of bacterial and fungal spores, and even vegetative cells of 

 Mycobacterium smegmatis, after 5 days' exposure to ultrahigh vacuum at pres- 

 sures below 10~^ mm. of Hg. (Portner et al., 1961). 



Table 1 



Environmental Limits of Temperature, Eh (at the Prevailing pH), pH, Hydrostatic 



Pressure, and Salinity for Growth and Reproduction 



OF Microorganisms 



(8) Survival of many microorganisms after prolonged exposure to tempera- 

 tures approaching absolute zero (Belehradek, 1935; Becquerel, 1950). Life 

 may, in some cases, be capable of almost infinite preservation under such condi- 

 tions. 



One could multiply the examples at greater length, but those already pre- 

 sented suffice to make the point. 



General Remarks 



In TABLE 1 are summarized the ranges of temperature. Eh, pH, hydrostatic 

 pressure, and salinity that still permit growth and reproduction of one or more 

 microorganisms. It is not maintained that growth is anywhere near maximal 

 under the extreme conditions referred to, merely that it does occur. Selection 

 and mutation over long periods of time could doubtlessly result in a further 

 widening of the observed limits. It should also be stressed in this connection 

 that scientists are inchned to study single factors taken one at a time. When 

 two or more environmental factors show antagonistic effects, as is the case 

 with temperature and pressure, one can expect to find an increased tolerance 

 to each factor using combined action. 



