3 Populations and Pathways
101
3.4.4.1 Hydrothermal Vents
Hydrothermal vents are characterized by very specific physical and chemical properties, such as elevated pressure (up to 420 atm), high and abruptly changing
temperature (from 2–4 ◦ C to 400 ◦ C) that can occur both spatially (within tens of cm:
Piccino et al. 2004) and temporally (10–50 ◦ C within a minute: Le Bris et al. 2005),
high levels of sulphide and/or methane that can fuel endosymbioses (Childress and
Fisher 1992) and chemical toxicity (heavy metals and radionuclides: Cherry et al.
1992, Luther et al. 2001) and the complete absence of light. However, numerous living organisms such as shrimps, clams, mussels, giant tubeworms, crabs and fishes
have been discovered in those environments. These organisms have developed different adaptive strategies, which ensure their exploitation of the hydrothermal vent
fluid. The most studied adaptations are:
• Symbiosis as a response to the absence of photosynthesis that has led to a food
chain based on primary production of energy and organic molecules by chimiolithoautotrophic bacteria (Minic and Herve 2004, Stewart and Cavanaugh 2006,
Duperron et al. 2007).
• Adaptation to high temperatures (Gaill et al. 1995, Sicot et al. 2000)
• Adaptation to toxicants (Company et al. 2004)
• Adaptation to hypoxia/anoxia (Hourdez and Weber 2005).
Studies of adaptation to high temperatures have essentially concentrated on bacteria. These show some general features, such as an increase in charged amino
acids, proline residues and replacement of some lysines by arginine, which increases
hydrogen bonds (Kumar et al. 2000, Nishio et al. 2003, Robinson et al. 2006).
Similar patterns are observed in eukaryote species such as A. pompejana, which
lives in a hotter part of this environment than P. grasslei. Analyses of aminoacid composition have revealed a significant increase in positively charged residues
together with an increase in protein hydrophobicity (Jollivet et al. in prep). Some
specific proteins have been carefully studied in terms of their thermostability, for
example collagen (Sicot et al. 2000), mitochondrial (Dahlhoff et al. 1991) and cytoplasmic (Jollivet et al. 1995) respiratory chain proteins and haemoglobins (see for
review Hourdez and Weber 2005). In the specific case of collagen, proline hydroxylation seems to play a crucial role in enhancing molecular thermostability and
therefore it is suggested that post-translational processes are also key factors in
adaptation to high thermal regimes.
Regarding the adaptation processes linked to the presence of toxicants and
hypoxia/anoxia, very few studies have been conducted and most are concerned with
the mussel genus and the effect of heavy metals or oxidative stress on enzymatic
activities (Company et al. 2008) or specific gene expression such as metallothioneins
(Hardivillier et al. 2006). Pruski and Dixon (2003) also showed a positive correlation between the levels of DNA strand breakage and HSP70 protein expression in
response to decompression and to oxidative stress. The molecular analyses of the
giant HBL-Haemoglobin of deep-sea vent annelids are a good example typifying
101
3.4.4.1 Hydrothermal Vents
Hydrothermal vents are characterized by very specific physical and chemical properties, such as elevated pressure (up to 420 atm), high and abruptly changing
temperature (from 2–4 ◦ C to 400 ◦ C) that can occur both spatially (within tens of cm:
Piccino et al. 2004) and temporally (10–50 ◦ C within a minute: Le Bris et al. 2005),
high levels of sulphide and/or methane that can fuel endosymbioses (Childress and
Fisher 1992) and chemical toxicity (heavy metals and radionuclides: Cherry et al.
1992, Luther et al. 2001) and the complete absence of light. However, numerous living organisms such as shrimps, clams, mussels, giant tubeworms, crabs and fishes
have been discovered in those environments. These organisms have developed different adaptive strategies, which ensure their exploitation of the hydrothermal vent
fluid. The most studied adaptations are:
• Symbiosis as a response to the absence of photosynthesis that has led to a food
chain based on primary production of energy and organic molecules by chimiolithoautotrophic bacteria (Minic and Herve 2004, Stewart and Cavanaugh 2006,
Duperron et al. 2007).
• Adaptation to high temperatures (Gaill et al. 1995, Sicot et al. 2000)
• Adaptation to toxicants (Company et al. 2004)
• Adaptation to hypoxia/anoxia (Hourdez and Weber 2005).
Studies of adaptation to high temperatures have essentially concentrated on bacteria. These show some general features, such as an increase in charged amino
acids, proline residues and replacement of some lysines by arginine, which increases
hydrogen bonds (Kumar et al. 2000, Nishio et al. 2003, Robinson et al. 2006).
Similar patterns are observed in eukaryote species such as A. pompejana, which
lives in a hotter part of this environment than P. grasslei. Analyses of aminoacid composition have revealed a significant increase in positively charged residues
together with an increase in protein hydrophobicity (Jollivet et al. in prep). Some
specific proteins have been carefully studied in terms of their thermostability, for
example collagen (Sicot et al. 2000), mitochondrial (Dahlhoff et al. 1991) and cytoplasmic (Jollivet et al. 1995) respiratory chain proteins and haemoglobins (see for
review Hourdez and Weber 2005). In the specific case of collagen, proline hydroxylation seems to play a crucial role in enhancing molecular thermostability and
therefore it is suggested that post-translational processes are also key factors in
adaptation to high thermal regimes.
Regarding the adaptation processes linked to the presence of toxicants and
hypoxia/anoxia, very few studies have been conducted and most are concerned with
the mussel genus and the effect of heavy metals or oxidative stress on enzymatic
activities (Company et al. 2008) or specific gene expression such as metallothioneins
(Hardivillier et al. 2006). Pruski and Dixon (2003) also showed a positive correlation between the levels of DNA strand breakage and HSP70 protein expression in
response to decompression and to oxidative stress. The molecular analyses of the
giant HBL-Haemoglobin of deep-sea vent annelids are a good example typifying