The high temperature fluids emerging from black smokers were sampled microbiologically by Baross during the Alvin Rise Expedition to 21°N in 1979. He and his colleagues
reported the presence of viable, extremely thermophilic microorganisms in samples of
black-smoker effluent with temperatures as high as 306°C (Baross, Lilley, and Gordon,
1982). These bacteria grew rapidly at 100°C and atmospheric pressure, using inorganic
sources of carbon, nitrogen, and energy to produce biomass and a number of gases,
including methane (Baross, Lilley, and Gordon 1982). The full impact of this discovery
was realized when we obtained evidence that one of these cultures could also be grown
under controlled laboratory conditions at the hydrostatic vent pressure of 265 atm and
temperatures of at least 250°C (Baross and Deming, 1983 ; Baross, Deming, and Becker
1984). These results indicated the upper temperature limit for microbial growth to be at
least 140°C higher than previously recorded (Stetter 1982) and raised new questions
on the origin of life (Nickerson 1984 ; Baross and Hoffman 1985 ; Yanagawa and Kojima
1985), prokaryotic evolution (Baross and Hoffman 1985), marine geochemistry, exobiology, and industrial microbiology (Sonnleitner and Fiechter 1983 ; Deming 1986). They
also met with considerable septicism (Trent, Chastain, and Yayanos 1984 ; White 1984),
as discussed further below.
The possibility that bacteria or their enzymes could function at temperatures above
100°C, if pressure was applied to prevent a phase change from liquid to vapor, had been
considered earlier (Zobell 1958 ; Morita and Haight 1962; Morita and Mathemeier 1964;
Brock 1978 ; Heinen and Lauwers 1981 , and Stetter 1982), but not tested above 110°C.
Prior to the Rise Expedition of 1979, there was no known marine habitat where seawater
reached extreme temperatures but remained liquid due to hydrostatic pressure and, thus,
little incentive to do more than propose the possibility of life in seawater at temperatures
above 100°C. Even after the discovery of hydrothermal vents, black smokers, and liquid
seawater at superheated temperatures, most microbiologists with access to vent samples
focused their studies on surfaces, animal tissues, and water samples at temperatures of
40°C or lower (Karl, Wirsen, and Jannasch 1980). After all, marine environments
have been viewed traditionally as habitats for psychrophilic and mesophilic, but not
thermophilic, bacteria. Furthermore, temperatures above 100°C at vapor pressure have
been known to degrade biomolecules (DNA, protein, etc.) in aqueous solution and are
used regularly in autoclaves to kill most bacteria.
Our experiments (Baross and Deming 1983) were novel, not so much because we tested
extreme temperatures, but because we used a deep-sea hydrostatic pressure of 265 atm
(and not vapor pressure) and an inoculum of potentially new microbial forms of life,
cultured from a hot, pressurized deep-sea environment and already known to grow at
100°C at 1 atm (Baross, Lilley, and Gordon 1982). The thermostability of previously
characterized, extremely thermophilic bacteria or their biomolecules under deep-sea
hydrostatic pressures is virtually unknown (Zobell 1958; Morita and Haight 1962; and
Morita and Mathemeier 1964). It is well known, however, that the characteristics of
naked DNA, free amino acids, or other biomolecules in aqueous solution differ from their
characteristics as bound components in a complex, living organism uniquely adapted to
its environment (Heden 1964). Well before our findings were published, others had
documented the existence of thermophilic bacteria in shallow terrestrial and submarine
hot springs that were capable of growth 10-20°C above the melting point of naked DNA
(Brock 1978; Heinen and Lauwers 1981, and Stetter 1982). Although the effects of
elevated hydrostatic pressure on such organisms were unexplored, slight gas pressures
had been used to achieve growth at 105°C (Heinen and Lauwers 1981) and at 110°C
(Stetter 1982), and even to keep some eukaryotic forms of life such as crustacean eggs
(Carlisle 1968) and fly larva (Hinton 1960) viable at 103°C. At this writing, there appears
326
reported the presence of viable, extremely thermophilic microorganisms in samples of
black-smoker effluent with temperatures as high as 306°C (Baross, Lilley, and Gordon,
1982). These bacteria grew rapidly at 100°C and atmospheric pressure, using inorganic
sources of carbon, nitrogen, and energy to produce biomass and a number of gases,
including methane (Baross, Lilley, and Gordon 1982). The full impact of this discovery
was realized when we obtained evidence that one of these cultures could also be grown
under controlled laboratory conditions at the hydrostatic vent pressure of 265 atm and
temperatures of at least 250°C (Baross and Deming, 1983 ; Baross, Deming, and Becker
1984). These results indicated the upper temperature limit for microbial growth to be at
least 140°C higher than previously recorded (Stetter 1982) and raised new questions
on the origin of life (Nickerson 1984 ; Baross and Hoffman 1985 ; Yanagawa and Kojima
1985), prokaryotic evolution (Baross and Hoffman 1985), marine geochemistry, exobiology, and industrial microbiology (Sonnleitner and Fiechter 1983 ; Deming 1986). They
also met with considerable septicism (Trent, Chastain, and Yayanos 1984 ; White 1984),
as discussed further below.
The possibility that bacteria or their enzymes could function at temperatures above
100°C, if pressure was applied to prevent a phase change from liquid to vapor, had been
considered earlier (Zobell 1958 ; Morita and Haight 1962; Morita and Mathemeier 1964;
Brock 1978 ; Heinen and Lauwers 1981 , and Stetter 1982), but not tested above 110°C.
Prior to the Rise Expedition of 1979, there was no known marine habitat where seawater
reached extreme temperatures but remained liquid due to hydrostatic pressure and, thus,
little incentive to do more than propose the possibility of life in seawater at temperatures
above 100°C. Even after the discovery of hydrothermal vents, black smokers, and liquid
seawater at superheated temperatures, most microbiologists with access to vent samples
focused their studies on surfaces, animal tissues, and water samples at temperatures of
40°C or lower (Karl, Wirsen, and Jannasch 1980). After all, marine environments
have been viewed traditionally as habitats for psychrophilic and mesophilic, but not
thermophilic, bacteria. Furthermore, temperatures above 100°C at vapor pressure have
been known to degrade biomolecules (DNA, protein, etc.) in aqueous solution and are
used regularly in autoclaves to kill most bacteria.
Our experiments (Baross and Deming 1983) were novel, not so much because we tested
extreme temperatures, but because we used a deep-sea hydrostatic pressure of 265 atm
(and not vapor pressure) and an inoculum of potentially new microbial forms of life,
cultured from a hot, pressurized deep-sea environment and already known to grow at
100°C at 1 atm (Baross, Lilley, and Gordon 1982). The thermostability of previously
characterized, extremely thermophilic bacteria or their biomolecules under deep-sea
hydrostatic pressures is virtually unknown (Zobell 1958; Morita and Haight 1962; and
Morita and Mathemeier 1964). It is well known, however, that the characteristics of
naked DNA, free amino acids, or other biomolecules in aqueous solution differ from their
characteristics as bound components in a complex, living organism uniquely adapted to
its environment (Heden 1964). Well before our findings were published, others had
documented the existence of thermophilic bacteria in shallow terrestrial and submarine
hot springs that were capable of growth 10-20°C above the melting point of naked DNA
(Brock 1978; Heinen and Lauwers 1981, and Stetter 1982). Although the effects of
elevated hydrostatic pressure on such organisms were unexplored, slight gas pressures
had been used to achieve growth at 105°C (Heinen and Lauwers 1981) and at 110°C
(Stetter 1982), and even to keep some eukaryotic forms of life such as crustacean eggs
(Carlisle 1968) and fly larva (Hinton 1960) viable at 103°C. At this writing, there appears
326