Lecture 10
Energy and Life in Unique Environments on Earth
(Chapter 3 of Bennet)

What are the chemical pathways of life?

1.  Photosynthesis:

CO2 + H2O + Sunlight --------->CH2O + O2
        {Input}                                {output}

Plants use the catalyst, chlorophyll (the "green stuff"), to take CO2 from the air, H2O from the ground, and sunlight (to build more complex bonds) and produce complex hydrocarbons, like plant cell walls.

    How it works:

i.  the energy from the sunlight breaks the bonds of the CO2 and H2O

CO2 = C + O2

H2O = 2H+ + ½O2 + 2e-

ii.  the H+ produced increases the production of ATP

iii. the ATP produced is then used to drive chemical reactions inside the plant cell (like build more cellular wall tissue).

2.  Oxidation:

The reverse of photosynthesis.  An example is aerobic respiration.

CH2O + O2----->CO2 + H2O + Energy

Oxidation of the carbon molecule produces energy which builds up ATP and can be used to build up cells or stored for later use.  Therefore, animals eat plants to gain energy or bacteria eat free standing molecules, also to acquire energy.

3.  Fermentation:

No free O2 or sunlight.

C6H12O6---->2C2H6O + 2CO2 + Energy
{glucose}                {ethanol}

*the bacteria in the lower levels of stromatolites use Fermentation to survive without O2 or sunlight.

Chemistry and life in unique environments:

1.  What if you have NO organic molecules and NO sunlight?

--Oxidizing Fe--

In mine tailings (which are very acidic), iron-oxidizing bacteria--Thiobacillus ferrooxidans--thrive.

2.  What if you have NO sunlight, NO organic molecules and NO acidic?

--Hydgrogen Reducing--

Fe + H2O ---> Hydrogen gas

6H2 + 2O2 + CO2 ---->CH2O + 5H2O + Energy

(where 6H2 is hydrogen gas)

Hydrogen gas comes from the oxidation of Iron by the groundwater located deep within the Columbia River Basalts.

This hydrogen gas is then used by the bacteria living at more than 1 km below the surface to convert dissolved inorganic carbon into energy.

Unlike the Thiobacillus ferrooxidans, acidic conditions are not necessary to slow down the iron oxidation.

This is an ecosystem that can exist without sunlight, or organically processed carbon.  The bacteria exist completely independent of surface life. This ecosystem is referred to as being autotrophic (needing neither organic sources of carbon or photosynthesis to survive).

Would the bacteria in this example survive a great asteroidal impact?

Probably.  Because their survival is not predicated on the Earth's surface viability.

*Both #1 & #2, are examples of bacteria that obtain their energy by oxidizing iron.

Some other examples of alternative energy for biota:

3.  Sulfate based bacteria:

H2SO4 + 4H2 ----> H2S + 4H2O

(where H2SO4 is sulphate and 4H2 is hydrogen gas)

4.  Methanogenic bacteria can use:

CO2 + 4H2 ----> CH4 + 2H2O


4CO + 2H2O ---->CH4 +3CO2

5.  Acetalyne based bacteria:

2CO2 + 4H2 ----> CH3COOH + 2H2O

6.  Iron-reducing bacteria or Hydrogen-oxidizing bacteria

2Fe+3 + H2 ----> 2Fe+2 +2H+

An interesting example of an iron-reducing bacteria (or hydrogen-oxidizing) are the hyperthermophilic species.  These bacteria thrive in extremely hot environments such as 80°--125°C water.  They can be found at mid-ocean vents or in hot springs like the ones in Yellowstone, WY (both locations associated with past or recent volcanic activity).

The bacteria that live in mid-ocean spreading areas get their carbon from the seawater, but their major source of energy is the atmospheric CO2 that has dissolved in the oceans (recall the CO2 feedback cycle).  The CO2 is from inorganic sources; photosynthesis is not used.  The bacteria in this environment are thus referred to as chemoautotrophs.

The bacteria that live in hot springs, such as the ones in Yellowstone Park displays itself in vivid colors.  These bacteria are photosynthetic.

A final example of life in a very hostile environment is the microbes living in the harsh valleys of Antarctica.  This is a desert where water is scarce.  But bacteria live in rocks.  The rocks absorb sunlight when it's available and provide small amounts of water to the bacteria.  These bacteria are called lithoautotrophs, because they reside in rock and utilize CO2 from the atmosphere.

The above examples of life thriving in harsh conditions may seem unusual, but they are thought to be the "norm".  The kinds of life we are most familiar with, such as the life that resides in our classrooms or in our backyards is NOT standard and is an evolution away from the standard form of life, such as the hyperthermophilics.

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