Prokaryotic Energetics and Metabolic Versatility

Question 1

What is a chemoorganotroph?

Answer 1

Organisms which oxidise the chemical bonds in organic compounds as their energy source. They also attain the carbon molecules that they need for cellular function from these organic compounds.
e.g. Glucose + O2 -> CO2 + H2O

Question 2

What is a chemolithotroph?

Answer 2

An organism that is able to use inorganic reduced compounds as a source of energy.
Electron Acceptor is commonly O2
Calvin cycle is the most common CO2 fixation mechanism.
e.g. H2 + O2 ->H2O

Question 3

What is a phototroph?

Answer 3

An organism that uses energy from sunlight to synthesise organic compounds for nutrition.

Question 4

Metabolism complexity in eukary. vs prokary.

Answer 4

Eukary. metabolism is very limited

Prokary. versatility lies in its metabolism (i.e. very complex).

Question 5

Fermentation

Answer 5

Produces products such as lactic acid and ethanol but is dependent on the species. Is useful for industrial purposes (bread and alcohol).
Does not require oxygen (anaerobic).

Question 6

Respiration (Aerobic vs anaerobic, in terms of terminal electron acceptors and relation to organic matter breakdown)

Answer 6

Aerobic: O2 is always the terminal electron acceptor. Completely degrades organic matter to CO2 and H2O.

Anaerobic: NO3-, SO4^2-, CO2, act as terminal electron acceptors. Produces CH4, CO2, H2, NH3, PO4^3- as a result of organic matter degradation.

Question 7

Denitrification

Answer 7

Defined as a microbial process reducing nitrate (NO3-) or nitrite (NO2-) to generate a proton motive force under anaerobic conditions. Mainly produces N2 with small amounts of NO and N2O.

Denitrifiers conserve more energy than other groups, so other groups are inhibited in their presence.
They remove nitrogen from wastewater treatment plants.

e.g. Paracoccus strains

Question 8

Metal Reduction

Answer 8

Oxidised metal ions can serve as electron acceptors in anaerobic respiration.
Microbes reduce metal ions as: 
- electron acceptors 
- for biosynthetic purposes
Both of these reduce metal toxicity

Water insoluble metals such as Fe(III) or Mn(IV) need to export electrons to reduce the electron acceptor.

e.g. Acidiphilum cryptum uses Fe(III) as an electron acceptor

Question 9

Sulfidogenesis

Answer 9

Many bacteria and archaea can use sulfate and elemental sulfur as electron acceptors.
SO4^2- —> H2S
Main habitat of sulfidogens = Sediments rich in organic electron donors (mainly fatty acids and alcohols) and sulfate. They cause corrosion of underground and underwater structure.

Question 10

Methanogenesis

Answer 10

Conversion of organic materials to methane (CH4).
Methanogens are strictly anaerobic archaea
CO2 is the electron acceptor
Common electron donors: methanol, acetate, carbon monoxide, H2.
They are grouped by which electron donor they use.

e.g. Methanobacterium palustre

Question 11

Syntrophic Associations

Answer 11

Bacteria of one kind working with bacteria of another to break down organic materials.
e.g. Methanogens and sulfidogens work together to remove hydrogen and acetate
Ethanol + H2O —> Acetate + H+ + 2*H2

Question 12

Element cycling under aerobic conditions can be exploited to clean up contaminated water and soil in a process called bioremediation.
TRUE OR FALSE

Answer 12

FALSE
Element cycling under ANAEROBIC conditions can be exploited to clean up contaminated water and soil in a process called bioremediation.

Question 13

Homoacetogenesis

Answer 13

Homoacetogens are strictly anaerobic bacteria that grow on the free energy available from the reduction of CO2 to acetate.
They also metabolise sugars and methanol to acetate.

Question 14

Organohalide Respiration

Answer 14

Halogenated compounds can be used as electron acceptors in a process called “dehalorespiration” or “organohalide respiration”.
Convert chlorinated compounds to non- or lesser halogenated compounds that are mostly less toxic to the environment.

Question 15

Hydrogen Oxidation

Answer 15

Various hydrogen-oxidizing bacteria grow chemolithotrophically on a H2 + CO2 mixture

• They use Hydrogen as their electron donor.
• Grow with the aid of hydrogenase, which oxidises H2 to generate ATP.

Question 16

Nitrification

Answer 16

Nitrifying bacteria oxidize ammonia and nitrite to generate energy.
Mostly obligately chemolithotrophic.
Widely distributed in soil and water. Required for the nitrogen cycle.

Question 17

Methane oxidation under anaerobic conditions:

Answer 17

anaerobic methane oxidation (AMO) is a microbially-mediated process ( by methanotrophs) which consumes a large part of this greenhouse gas in nature.
3 different processes:
- Sulfate-dependent AMO (S-DAMO)
- Nitrate/Nitrite-dependent AMO (N-DAMO)
- Metal ion-dependent AMO (M-DAMO)

Question 18

Oxidation of sulfur compounds:

Answer 18

Certain prokaryotes can use inorganic sulfur compounds as their energy source – these are sulfur bacteria.
They Fix CO2 through the Calvin cycle.

e.g Acidithiobacillus ferroxidans (bacteria): a major participant in consortia of microorganisms used for the industrial recovery of copper (bioleaching or biomining)

Question 19

Iron bacteria: Ferrous Iron Oxidation

Answer 19

Iron bacteria use the free energy generated from the oxidation of Fe2+ to fix CO2.
They are chemolithotrophs.

e.g. Gallionella ferruginea