Environmental microbiology

SS 5113

Bioenergetics of microorganisms 2 h WS All assessments 50%

Evolution of metabolic pathways 2 h

Techniques in environmental microbiology

3 h

Microbial communities 3 h

Biogeocycling of nutrients 4 h

Enzymes in the soil env. 4 h CR Presentation (15%)

Microorganisms as sinks and sources of pollutants

7 h

Principles of biological treatments 3 h

End term examination 2h 25%

Bioenergetics of microorganisms

Diversity of microbial metabolism

Metabolism

• The sum of the biochemical reactions required for energy generation and the use of energy to synthesize cell material from small molecules in the environment

Catabolism

Anabolism

Catabolism

Energy yielding metabolism

Anabolism

Biosynthetic metabolism

Energy sources

Metabolic products

Biopolymers

External nutrients

ATP

ADP

Heat

Simplest, oldest, least evolved

Occurs during fermentation, respiration

Substrate (organic) Product (organic) + ATP

Substrate level phosphorylation

Electron transport phosphorylation

• Complicated, evolved long after SLP

• Occurs during respiration, photosynthesis, lithotrophic metabolism, etc.

• Requiers:

en supply

(TCA cycle/photophosphorilation/reduced compound)

Membranes

Electron transport systems

en acceptor

ATPase enzymes

ETP

Electron donor

Electron transport system (ETS)

Electron acceptor

H+

Proton motive force (pmf)

Membrane bound ATP synthetase enzyme ATP

e-

ADP

H+

H+

Diversity of metabolism • Heterotrophic types

Fermentations

Respirations

• Lithotrophic types

e.g. nitrification, S oxidation

• Phototrophic metabolism

Oxygenic photosynthesis

Anoxygenic photosynthesis

Non-photosynthetic photophosphorylation

Heterotrophic types

Fermentation

• Partial oxidation of an organic compound using organic intermediates as en donors and en acceptors

• ATP produced by substrate level phosphorylation

• E.g.

Homolactic fermentation – Lactobacillus, Streptococci

Butyric acid fermentation – Clostridium

Butanol-acetone fermentation – C. acetobutylicum

Mixed acid fermentation - Enterobacteriaceae

Heterotrophic types

Respiration

• Complete oxidation of the substrate by an outside en acceptor

• ATP produced by SLP & ETP

• Essential structural metabolic components?

en supply - organic molecule via TCA cycle

en acceptor

O2 – Aerobic respiration

Other molecules – Anaerobic respiration

Lithotrophic type metabolism

• Use of an inorganic compound as energy source

• Produce ATP via ETP

• Essential structural metabolic components?

en supply - inorganic molecule

en acceptor

very often O2 – Aerobic respiration

Some use CO2 – Anaerobic respiration

Lithotrophy

Physiological group Energy

source Electron acceptor

Oxidized end product

Organisms

Hydrogen bacteria H2 O2 H2O

Methanogens H2O CO2

H2O

Nitrifiers NH3

NO2-

O2

NO2

-

NO3-

Methanotrophic bacteria

CH4 O2

CO2

Sulfur oxidizers H2S or S O2

SO4

2-

Iron bacteria Fe2+ O2 Fe3+

Phototrophic metabolism

• Use of an electromagnetic energy

Convert light energy to chemical energy (ATP)

• Produce ATP via ETP and photophosphorylation

• Three types

Oxygenic photosynyhesis

Anoxygenic photosynyhesis

Non-photosynyhetic photophosphorylation

Photosynthesis

Criteria Oxygenic p’sis Anoxygenic p’sis

Organisms Plants, Algae, Cyanobacteria

Purple Sulfur bacteria, Green Sulfur bacteria, Purple bacteria, Green bacteria

Type of Chlorophyll

Chlorophyll a Absorbs 650 – 750 nm

bacteriochlorophyll Absorbs 800 – 1000 nm

Produces O2 Yes No

Photosynthetic en donor

H2O H2S, other S compounds or organic compounds

Energy yield

• Redox reactions:

Oxidation is the loss of electrons and reduction is the gain of electrons. Electrons cannot exist in solution and the loss of electrons must be coupled to the gain of electrons

• Reduction potential:

This is a quantitqtive measure of the tendency for a substance to give up electrons in biological systems. It is measured in volts and generally at pH = 7.0

Relationship between free energy and reduction potential

Go = -nF Eh

Go = Change in Free energy

n = number of electrons in reaction

F = Faradays constant

Eh = E0 (acceptor) - E0 (donar)

ATP hydrolysis releases –31.8 kJ / mole so we need at least this amount of energy to make a phosphodiesterase bond in ATP.

Electron donor

Electron acceptor

Reduced end product

e- Electrode potential (V)

Energy generation (compared to H half cell) => G0 ’

H+ O2 H2O 2 +0.82 -2*96.48*(+0.82- (-0.42)) = -239 kJ

H+

CO2

methanol 6 -0.38 -23.2 kJ

H+

Fe3+ Fe2+

1 +0.76 -73.3 kJ

H+

NO3

- N2 5 +0.74 -559.6 kJ

H+

SO4

-2 H2S 8 -0.22 -154.4 kJ

H+

Fumarate

Succinate 2 +0.03 -86.8 kJ

0

+200

+400

+600

-200

Oxidized soil

Moderately reduced soil

Reduced soil

Highly reduced soil

O2 O2-

NO3- NO2

-, N2O, N2

MnO2 Mn2+

Fe2O3 Fe2+

SO42- S2-

CO2 CH4

Range in redox potentials in waterlogged soils and the location where the various en acceptors are active

Study questions • Find the electrode potential for following couples

• Fe2+/O2

• NO3-/Fe3+

• H2S/O2

• Fumarate/ NADH

• Do each of these reactions produce or consume energy?

• Do these looks like potential reactions in respiratory pathways?