water (freshwaters or oceans), hydrostatic pressure increases
by 10 MPa per kilometer. For instance, at a depth of 3 km in
the ocean, hydrostatic pressure is 30 MPa, 300 atm or 300 bars.
The choice of the oceans to explain the different pressure
units is justified, since the study of this environment gave
birth to the discovery and study of piezophilic
microorganisms, sometimes called piezomicrobiology.
Since about 2000, the word piezophile (from the Greek
“πı ´εση” which likes pressure) progressively replaced the
word barophile (from the Greek “βάρoςτΘ”, which likes
weight) that was used before (cf. Sect. 17.2.3).
Seventy percent of planet Earth is covered by seas and
oceans, with an average depth of 3,800 m. However, the
maximum depth recorded in the Marianna Trench is
10,790 m, which corresponds to an hydrostatic pressure of
110 MPa. For English-speaking authors, the term “deep sea”
corresponds to depth below 1,000 m. Such a depth exists for
88 % of the oceanic area, corresponding to 75 % of the total
volume of the oceans, and 62 % of the volume of the
biosphere. At the time of these estimations (about 1980),
the deep sea was one of the more important biotopes of the
planet influenced by hydrostatic pressure. Since that time,
subsurface habitats, exposed to elevated pressures and
inhabited by microorganisms, have been discovered: deep
aquifers, oil reservoirs, or deep-sea sediments. As we will
see, most of the Earth’s biosphere is inhabited by piezophiles
(cf. Sect. 9.6.4).
10.5.2 Deep-Sea Piezopsychrophiles: A Brief
History
In addition to depth and darkness, a main feature of deep-sea
habitats is a cold temperature, about 2
C, which is suitable
for psychrophiles (cf. Sect. 10.1).
The occurrence of bacteria living in oceanic waters and
sediments at a depth of 5,000 m has been shown by the French
microbiologist A. Certes, who studied samples collected by
the ships “Le Travailleur” and “Le Talisman” (1882–1883).
After this pioneer work, and 10 years later that of the US
scientist B. Fisher, deep-sea microbiology remained sleepy
until the major works of the US microbiologists Claude
Zobell and Richard Morita, who can be considered as the
“fathers” of marine microbiology (cf. Sect. 2.5).
Because of total darkness, there is no photosynthesis in
the deep sea, and consequently, the deep sea is an oligotrophic environment. One of the first topics addressed by deepsea microbiologists was the degradation of organic matter
under deep-sea conditions: low temperature and elevated
hydrostatic pressure. Many experiments under atmospheric
and hydrostatic pressure were carried out using surface and
deep-sea bacterial strains, deep-sea samples decompressed
or not. Most experiments showed that heterotrophic activity
and aerobic respiration of organic molecules were considerably slowed down by these deep-sea conditions. Probably,
very few free-living bacteria adapted to the deep-sea
environments existed (Jannasch and Wirsen 1973). The
study of some enzymatic activities such as chitinases under
elevated hydrostatic pressure also gave similar results:
activities were higher under atmospheric pressure. But the
microorganisms used for these various experiments,
although collected in the deep sea, were mostly originated
from the upper layers of the oceans. Further, the analysis of
deep-sea amphipods (crustaceans) or holothurians and fishes
showed the existence of true deep-sea piezophiles, particularly in their digestive tracts.
10.5.2.1 Some Piezopsychrophilic Bacteria
The first piezopsychrophilic bacteria were isolated and
described by A. Yayanos from the Scripps Institution for
Oceanography (California, USA). Strain CNPT3, belonging
to the genus Spirillum, was isolated from a dead amphipod,
captured in a trap at a depth of 5,600 m. This organism
isolated at 2
C and 57 MPa grows optimally in between
2 and 4
C, with a doubling time in between 4 and 13 h. At
the same temperature, but under atmospheric pressure, the
doubling time increases up to 3–4 days. Later, still from a
dead amphipod trapped at a depth of 10,476 m, strain MT41
was isolated. This organism grows optimally at 2
C and
69 MPa, with a doubling time of 25 h. No growth was
observed for pressures below 38 MPa, and the strains lost
their ability to form colonies after a few hours of exposure at
atmospheric pressure. Later on, a variety of aerobic heterotrophic piezopsychrophilic organisms were isolated often
from deep-sea animals, mostly by US and Japanese
scientists. Thanks to molecular phylogeny techniques,
these strains were described as novel species within the
genera Photobacterium or Shewanella or even novel genera
such as Colwellia or Moritella.
From the study of the growth of several piezophilic
strains, Yayanos showed several unique features for these
organisms. Particularly, he showed that piezophily was a
common feature of cold oceanic waters, at depths below
2,000 m, that seems to be a threshold for piezophily. He
also noted that the response to hydrostatic pressure varied
with the capture depth of the strain concerned. But in all
cases, the optimal pressure for growth of a given strain was
always lower than the pressure existing at the place where
the original sample was collected.
Although he produced a major contribution to deep-sea
microbiology, Yayanos himself noted that many questions
remained unanswered. Particularly, all these piezophilic
bacteria had been isolated from environments (deep-sea
animal digestive tracts) enriched in organic matter, while
the deep sea is globally oligotrophic (Yayanos 1986).
376
J.-L. Cayol et al.
by 10 MPa per kilometer. For instance, at a depth of 3 km in
the ocean, hydrostatic pressure is 30 MPa, 300 atm or 300 bars.
The choice of the oceans to explain the different pressure
units is justified, since the study of this environment gave
birth to the discovery and study of piezophilic
microorganisms, sometimes called piezomicrobiology.
Since about 2000, the word piezophile (from the Greek
“πı ´εση” which likes pressure) progressively replaced the
word barophile (from the Greek “βάρoςτΘ”, which likes
weight) that was used before (cf. Sect. 17.2.3).
Seventy percent of planet Earth is covered by seas and
oceans, with an average depth of 3,800 m. However, the
maximum depth recorded in the Marianna Trench is
10,790 m, which corresponds to an hydrostatic pressure of
110 MPa. For English-speaking authors, the term “deep sea”
corresponds to depth below 1,000 m. Such a depth exists for
88 % of the oceanic area, corresponding to 75 % of the total
volume of the oceans, and 62 % of the volume of the
biosphere. At the time of these estimations (about 1980),
the deep sea was one of the more important biotopes of the
planet influenced by hydrostatic pressure. Since that time,
subsurface habitats, exposed to elevated pressures and
inhabited by microorganisms, have been discovered: deep
aquifers, oil reservoirs, or deep-sea sediments. As we will
see, most of the Earth’s biosphere is inhabited by piezophiles
(cf. Sect. 9.6.4).
10.5.2 Deep-Sea Piezopsychrophiles: A Brief
History
In addition to depth and darkness, a main feature of deep-sea
habitats is a cold temperature, about 2
C, which is suitable
for psychrophiles (cf. Sect. 10.1).
The occurrence of bacteria living in oceanic waters and
sediments at a depth of 5,000 m has been shown by the French
microbiologist A. Certes, who studied samples collected by
the ships “Le Travailleur” and “Le Talisman” (1882–1883).
After this pioneer work, and 10 years later that of the US
scientist B. Fisher, deep-sea microbiology remained sleepy
until the major works of the US microbiologists Claude
Zobell and Richard Morita, who can be considered as the
“fathers” of marine microbiology (cf. Sect. 2.5).
Because of total darkness, there is no photosynthesis in
the deep sea, and consequently, the deep sea is an oligotrophic environment. One of the first topics addressed by deepsea microbiologists was the degradation of organic matter
under deep-sea conditions: low temperature and elevated
hydrostatic pressure. Many experiments under atmospheric
and hydrostatic pressure were carried out using surface and
deep-sea bacterial strains, deep-sea samples decompressed
or not. Most experiments showed that heterotrophic activity
and aerobic respiration of organic molecules were considerably slowed down by these deep-sea conditions. Probably,
very few free-living bacteria adapted to the deep-sea
environments existed (Jannasch and Wirsen 1973). The
study of some enzymatic activities such as chitinases under
elevated hydrostatic pressure also gave similar results:
activities were higher under atmospheric pressure. But the
microorganisms used for these various experiments,
although collected in the deep sea, were mostly originated
from the upper layers of the oceans. Further, the analysis of
deep-sea amphipods (crustaceans) or holothurians and fishes
showed the existence of true deep-sea piezophiles, particularly in their digestive tracts.
10.5.2.1 Some Piezopsychrophilic Bacteria
The first piezopsychrophilic bacteria were isolated and
described by A. Yayanos from the Scripps Institution for
Oceanography (California, USA). Strain CNPT3, belonging
to the genus Spirillum, was isolated from a dead amphipod,
captured in a trap at a depth of 5,600 m. This organism
isolated at 2
C and 57 MPa grows optimally in between
2 and 4
C, with a doubling time in between 4 and 13 h. At
the same temperature, but under atmospheric pressure, the
doubling time increases up to 3–4 days. Later, still from a
dead amphipod trapped at a depth of 10,476 m, strain MT41
was isolated. This organism grows optimally at 2
C and
69 MPa, with a doubling time of 25 h. No growth was
observed for pressures below 38 MPa, and the strains lost
their ability to form colonies after a few hours of exposure at
atmospheric pressure. Later on, a variety of aerobic heterotrophic piezopsychrophilic organisms were isolated often
from deep-sea animals, mostly by US and Japanese
scientists. Thanks to molecular phylogeny techniques,
these strains were described as novel species within the
genera Photobacterium or Shewanella or even novel genera
such as Colwellia or Moritella.
From the study of the growth of several piezophilic
strains, Yayanos showed several unique features for these
organisms. Particularly, he showed that piezophily was a
common feature of cold oceanic waters, at depths below
2,000 m, that seems to be a threshold for piezophily. He
also noted that the response to hydrostatic pressure varied
with the capture depth of the strain concerned. But in all
cases, the optimal pressure for growth of a given strain was
always lower than the pressure existing at the place where
the original sample was collected.
Although he produced a major contribution to deep-sea
microbiology, Yayanos himself noted that many questions
remained unanswered. Particularly, all these piezophilic
bacteria had been isolated from environments (deep-sea
animal digestive tracts) enriched in organic matter, while
the deep sea is globally oligotrophic (Yayanos 1986).
376
J.-L. Cayol et al.