TITLE:  A Pressure-Filled Life
      AUTHOR:  GILLIS, ANNA MARIA
     JOURNAL:  BioScience
    CITATION:  October, 1994, 44: 584-586.
        YEAR:  1994
    PUB TYPE:  Article
 IDENTIFIERS:  MICROORGANISM EVOLUTION; PSYCHROPHILIC BACTERIA; THERMOPHILIC 
               BACTERIA; BAROTOLERANCE; PRESSURE ADAPTATIONS; ARCHAEA; 
               EVOLUTION/MICROORGANISMS
    ABSTRACT:       Terrestrial dwellers operate best at a pressure of one 
               atmosphere (atm); but microorganisms are more adaptable. Some 
               thrive thousands of meters beneath the sea, where they are 
               subjected to pressures of hundred of atmospheres. Others, 
               seemingly suited to life at one atmosphere, function well 
               when exposed to a range of pressures. This adaptability 
               raises questions about how microorganisms adjust to pressure 
               and what these adaptions may say about their evolution. But, 
               so far, pressure as an environmental factor for 
               microorganisms has not been studied extensively.
                    Organisms of interest include psychrophilic and 
               thermophilic bacteria, and archaea (single-celled organisms 
               that fall between the bacteria and eukaryotes). The 
               psychrophiles thrive in water colder than 15 degrees C, while 
               the thermophiles do well at temperatures above 70 degrees C. 
               Some of these later organisms have been found in underwater 
               vents, called smokers, some 2,000-3,000 m below the ocean 
               surface, at pressures around 265-370 atm. Adaptations for 
               high pressure in microorganisms are called barotolerance. 
               Understanding how these barophiles work might improve the 
               understanding of pressure's impact on protein structure and 
               DNA replication.
                    Scientists know little of the biochemistry, molecular 
               biology, and genetics of pressure adaptation. Laboratory 
               studies of about two dozen ocean-dwelling microorganisms from 
               a variety of depths suggest that many experience optimal 
               growth in the laboratory at pressures at or above the 
               pressure at which they were collected. Others caution, 
               however, that some of these findings may be a result of 
               culture conditions. In the laboratory, for instance, the 
               microorganisms receive large amounts of high-quality 
               nutrients and endure no competition. To know with certainty 
               whether organisms in their native habitat require pressure to 
               survive, laboratory parameters must more closely parallel 
               environmental conditions.
                    Finding organisms that do well under both high 
               temperature and pressure could alter theories about the 
               evolution of microorganisms. The consensus is that early 
               organisms developed under high temperatures and low pressure. 
               But proving that particular thermophilic microorganisms are 
               obligate barophiles in their native environment would hint 
               that life could have evolved deep in the sea.