Energyyielding reactions of Hyperthermophiles

Electron Donor Electron Acceptor Product

S0 (Pyrite)

S0 (Pyrite)

G2 (traces) G2

Methane Magnetite Hydrogen Sulfide Nitrogen (NH3) Water

H2SO4(+FeSO4)

Source of Cell Carbon: CO2

Additional Growth requirements: Heat, Trace minerals, Liquid water

Fig. 7.5. Main energy-yielding reactions in chemolithoautotrophic HT (schematic drawing).

Table 7.1. Growth conditions and morphology of hyperthermophiles

Species

Min.

Opt.

Max.

pH

Aerobic

Morphology

Temp

Temp

Temp

(ae) vs.

(°C)

(°C)

(°C)

anaerobic (an)

Sulfolobus

60

75

85

1-5

ae

lobed cocci

acidocaldarius

Metallosphaera

50

75

80

1-4.5

ae

cocci

sedula

Acidianus

60

88

95

1.5-5

ae/an

lobed cocci

infernus

Stygiolobus

57

80

89

1-5.5

an

lobed cocci

azoricus

Thermoproteus

70

88

97

2.5-6

an

regular rods

tenax

Pyrobaculum

74

100

103

5-7

an

regular rods

islandicum

Pyrobaculum

75

100

104

5.8-9

ae/an

regular rods

aerophilum

Thermofilum

70

88

95

4-6.5

an

slender regular

pendens

rods

Desulfurococcus

70

85

95

4.5-7

an

cocci

mobilis

Thermosphaera

67

85

90

5-7

an

cocci in

aggregans

aggregates

Sulfophobococcus

70

85

95

6.5-8.5

an

cocci

zilligii

Staphylothermus

65

92

98

4.5-8.5

an

cocci in

marinus

aggregates

Thermodiscus

75

88

98

5-7

an

disks

maritimus

Aeropyrum

70

90

100

5-9

ae

irregular cocci

pernix

Stetteria

70

95

102

4.5-7

an

irregular disks

hydrogenophila

Ignicoccus

65

90

100

3.9-6.3

an

irregular cocci

islandicus

Pyrodictium

82

105

110

5-7

an

disks with

occultum

cannulae

Hyperthermus

80

101

108

7

an

lobed cocci

butylicus

Pyrolobus

90

106

113

4.0-6.5

ae/an

lobed cocci

fumarii

Thermococcus

75

87

93

4-7

an

cocci

celer

Pyrococcus

70

100

105

5-9

an

cocci

furiosus

Archaeoglobus

60

83

95

5.5-7.5

an

irregular cocci

fulgidus

Ferroglobus

65

85

95

6-8.5

an

irregular cocci

placidus

Methanothermus

65

88

97

5.5-7.5

an

rods in clusters

sociabilis

Methanopyrus

84

98

110

5.5-7

an

rods in chains

kandleri

Methanococcus

45

88

91

5-7.5

an

irregular cocci

igneus

Thermotoga

55

80

90

5.5-9

an

rods with

maritima

sheath

Aquifex

67

85

95

5.4-7.5

ae

rods

pyrophilus

decaying cells). Heterotrophic HT gain energy either by aerobic or different types of anaerobic respiration, using organic material as electron donors, or by fermentation.

7.5.2 General physiologic properties

HT are adapted to environmental factors including composition of minerals and gases, pH, redox potential, salinity and temperature. Similar to mesophiles, they grow within a temperature range of about 25-30 °C between the minimal and maximal growth temperature (Table 7.1). Fastest growth is obtained at their optimal growth temperature, which may be up to 106 °C. Generally, HT do not propagate at 50 °C or below. Although unable to grow at the low ambient temperatures, they are able to survive for years. Based on their simple growth requirements, HT could grow on any hot, wet place, even on other planets and moons of our solar system, like Mars and Europa. Today, the surface of Mars is too cold and contains no liquid water and therefore is hostile to life as it is known on Earth. However, in a depth of a few kilometres below the permafrost layer, there may be hot liquid water and nutrients to support growth of HT. Life could have spread onto Mars via meteorites during the great bombardment, about 4 GA ago. At that time, the surface of Mars had been much hotter and contained liquid water, therefore being favourable to HT.

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