1.2 THE ENERGY OF LIFE
CHEMOSYNTHESIS
Is there life on Mars? Is there no life on Mars?
Science doesn’t know. Science isn’t quite up to speed yet!
Organisms capable of chemosynthesis occupy a unique place in the energetics of life. Chemosynthesis is a mode of autotrophic nutrition in which the primary energy source is derived from the oxidation of inorganic compounds – such as sulphur, iron, hydrogen, and nitrogen – as well as methane.
Chemoautotrophs do not depend directly on solar energy and thrive in some of the planet’s most extreme and inaccessible environments: the deep ocean, beneath the seafloor, within soils, and inside wetlands. They function as natural consumers of toxic substances, drive the formation of mineral deposits, and naturally purify wastewater.
Today, the global impact of chemosynthesis is being profoundly reevaluated. Discoveries have revealed that the biomass of the deep subterranean biosphere beneath the ocean floor – which includes chemosynthetic, anaerobic, methane-oxidizing archaea – is comparable to, or may even exceed, the biomass of the entire remaining biosphere. Consequently, scientists have hypothesized that chemosynthesis could sustain microbial life beneath the surface of Mars and other planetary bodies.
Life is far more extraordinary than it appears!
CHEMOAUTOTROPHS: WHO ARE THEY?
| CHEMOAUTOTROPHIC GROUP | SUBSTRATE OXIDIZED (ENERGY SOURCE) |
|---|---|
| Nitrifying Bacteria Nitrosomonas Nitrobacter Nitrosococcus | Ammonia (NH₃) → nitrites (NO₂⁻) → nitrates (NO₃⁻) |
| Sulphur-Oxidizing (Thionic) Bacteria Beggiatoa Thiobacillus | Hydrogen sulphide (H₂S), thiosulfates, sulphur (S) → sulphates (SO₄²⁻) |
| Iron-Oxidizing Bacteria Geobacter Gallionella Leptothrix | Ferrous iron (Fe²⁺) → ferric iron (Fe³⁺) |
| Hydrogen-Oxidizing Bacteria Hydrogenomonas | Molecular hydrogen (H₂) |
| Methanogenic Archaea (Methanogens) Methanobacterium Methanosarcina Methanococcus | Hydrogen (H₂) + carbon dioxide (CO₂) → methane (CH₄) |
PARTNERS IN CHEMOSYNTHESIS
To thrive in the deep ocean where sunlight never penetrates, organisms can either directly harness the chemical energy of hydrothermal vents or cooperate with those that do. Symbiosis with chemoautotrophic bacteria is an evolutionary strategy that enables life to flourish in these extreme environments.
ENDOSYMBIOSIS
Example: Riftia pachyptila (Vestimentiferan tube worm)
BIOLOGICAL MECHANICS:
- The tube worm absorbs O₂, H₂S, and CO₂ directly from the water.
- Specialized haemoglobin binds O₂ and H₂S into a unique HSHbO₂ complex and transports it to the trophosome.
- Bacteria within the trophosome oxidize H₂S to generate ATP and NAD(P)H.
- Utilizing the Calvin cycle, the bacteria fix CO₂ to synthesize organic molecules.
- These organic nutrients are released directly into the worm’s bloodstream and distributed throughout its body.
EXOSYMBIOSIS
Example: Yeti Crab (Kiwa hirsuta)
BIOLOGICAL MECHANICS:
- The crab extends its densely bristled claws directly into the nutrient-rich fluid streams of a hydrothermal vent.
- The water flow supplies H₂S (hydrogen sulphide) and O₂ (oxygen).
- Bacteria living on the setae (bristles) oxidize the sulphur compounds to generate metabolic energy (ATP).
- Using this energy, the bacteria drive the reductive tricarboxylic acid cycle to fix CO₂ and produce organic matter.
- As the bacteria proliferate on the bristles, the crab scrapes off the accumulated microbial biomass and consumes it.