Chemolithoautotrophy

Question 1

Definition of Chemolithoautotrophy

Answer 1

Organisms which use inorganic carbon compounds for energy source (PEDs).
Fix CO2 as carbon source, use chemical energy.
Rock eaters.
Oxidising inorganic carbon compounds.

Question 2

Is Chemolithoautotrophy oxidising or reducing species?

Answer 2

Oxidising

Question 3

How does Chemolithoautotrophy compare to Chemoheterotrophy in terms of energetics?

Answer 3

Chemolithoautotrophy is less energetically favourable then chemoheterotrphy.

• Delta E greater for chemoheterotrophic reactions
• Electron donors for chemolithoautotrophy are required for ATP generation (catabolism) and CO2 fixation (anabolism).

Question 4

Examples of Chemolithoautotrophic PEDS?

Answer 4

H2
CH4
S
S3O32- 
Fe(II), Mn(II), NH4+ 

Not organic carbon.

Question 5

Examples of Chemolithoautotrophic TEAs?

Answer 5

Usually O2

If not available:
- NO3-, Mn(IV), Fe(III), SO42-, S

Question 6

Chemolithoautotrophy thermodynamic energy yeilds, in decreasing order?

Answer 6

Hydrogen Oxidisers 
Methanogens 
Methanotrophs 
Sulphur Oxidisers 
Iron Oxidisers 
Manganese Oxidisers 
Nitrogen Oxidisers

Question 7

Examples of Hydrogen Oxidisers and their TEAs?

Answer 7

1. Aerobes - use O2 as TEA
2. Facultative Anaerobes - Use O2 as TEA, if not available use NO3-, Mn(IV), Fe(III).
3. Obligate Anaerobes - use SO42- or CO2, always anoxic.
4. Mixotrophs - inc. autotrophs (fix CO2) or heterotrophs

Question 8

Explain how methanogens work?

Answer 8

Form Methane.
Can either be:
Chemolithoautotrophs - fix CO2
Chemoheterotrophs - use organic C

Question 9

Explain how methanotrophs work?

Answer 9

Consume (oxidise) methane.
Can be either chemolithoautotrophs or chemoheterotrophs.
Found where methane is abundant e.g., hydrothermal seafloor methane.

Question 10

What are the two types of sulphur oxidisers?

Answer 10

Gradient Organisms

Acidophiles

Question 11

What conditions do Gradient Organisms grow?

sulphur oxidiser

Answer 11

Microaerophillic (sub-oxic)
Neutral pH
e.g., sulphur springs, microbial mats.

Require low O2 and reduced sulphur.

Question 12

What bacteria catalyse abiotic sulphur oxidation at low O2 levels?

Answer 12

Beggiatoa

Question 13

PED and TEAs used by Acidophiles?

sulphur oxidiser

Answer 13

Grow in acid rich environments.

PEDs - H2S, hydrogen sulphide, is most common
TEAs - O2 is most common, but can also use NO3-, NO2-, Fe(III).

Question 14

Bacteria used to speed up oxidation by acidophiles?

sulphur oxidiser

Answer 14

Acidothiobacillus

Acidic conditions mean sulphur can stay in solution, this means bacteria are required to speed up sulphur oxidation.

Question 15

What are the two types of Iron Oxidisers?

Answer 15

Neutrophiles

Acidophiles

Question 16

What conditions do neutrophiles grow?

iron oxidiser

Answer 16

Circumneutral (roughly neutral)

Low O2 environments - microaerophillic

Question 17

Examples of neutrophiles and acidophiles?

iron oxidisers

Answer 17

Neutrophiles - Gallionella

Acidophiles - Acidothiobacillus, Acidiothiobacillus ferrooxidans.

Question 18

Explain the role of Manganese Oxidisers?

Answer 18

Grow at neutral pH in oxic conditions.

Abiotic oxidation of Mn(II) to Mn(III) or Mn(IV) is slow.

Mn-oxidising bacteria, usually produced in the environment, catalyse the reaction.

Mn-oxides encrust cells or form sheaths

Question 19

Explain Nitrogen Oxidisers?

Answer 19

PED = NH4+ (ammonium)
TEA = O2

e.g., NH4+ > NO2- > NO3-

Common in habitats with high ammonium.

Can also get Anammox bacteria (anaerobic oxidisers).
Use NO2- as TEA rather than O2.

Question 20

Nitrogen Oxidisers examples?

Answer 20

NH4+ > NO2- = catalysed by Nitrosomonas

NO2- > NO3- = catalysed by Nitrobacter