Post on 21-Feb-2022
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?