Microbiology 28.03.2018 Helmut Pospiech http://www.thescientificcartoonist.com/?p=107
Energy metabolism of Microorganisms Fermentation ADP +Pi Motility ATP Active transport (nutrient uptake)
Lactic Acid Fermentation 2 ATP
Fermentation the Art of Effective NADH Regeneration In every fermentation, there has to be atomic and redox balance Simplest way to keep redox balance is to produce H 2 H 2 is then used by other microorganisms
Clostridial Fermentations III
Fermentations lacking substrate level phosphorylations ΔG 0 = -20.5 kj ΔG 0 = -26.7 kj Succinate fermentation Propionigenium modestum Energy produced is not sufficient for direct ATP generation Na + ion is pumped across the cytoplasmic membrane Oxalate fermentation Oxalobacter formigenes Energy conserved as protomotoric force (H + gradient) The end of the line for fermentation?
No! Syntrophy Two different microorganisms cooperate to degrade a substance that neither can utilise alone Mainly secondary fermentations Interspecies H 2 transfer Keeps H 2 concentrations low and drives the reaction to the product side although the ΔG 0 is positive Mainly fermentation of alcohols and fatty acids
Microbial Respriation
Aerobic Oxidation of Pyruvate and Fetty Acids in Mitochondria outer mitochondrial membrane (permeable for metabolites) CO 2 inner mitochondrial membrane Pyruvate dehydrogenase Citrate cycle Fetty acid Pyruvate ATP + HSCoA Transporter AMP + PP i Acyl- CoA O O CH 3 C C HSCoA CO 2 OH b-oxidation Transporter NAD + Acyl- CoA NAD + O CH 3 C SCoA 2 CO 2 Acetyl-CoA + NADH 3 NAD + 3 NADH FAD FADH 2 HSCoA HSCoA FADH 2 NADH FAD P i + GDP GTP CO 2 NADH NAD + Electron Shuttle NAD + NADH Respiratory chain 2 e + 2 H + + ½ O 2 Succinate NAD + Fumarate I FAD III O 2 IV H 2 O H 2 O ATP- Synthase ATP ADP + P i Transporter ATP ADP P i OH II H + H + H + Elektron transport chain 3 H + F 0 F 1 complex
Redox tower of mitochondrial respiratory chain
Mitochondrial respiration e - donor e - donor e - donor Proton pumping e - donor ATP hydrolysis e - acceptor
Anaerobic Respiration The Use of Alternative Electron Acceptors instead of O 2 O 2 is the acceptor for the respiratory chain since it optimises the energy gain of the reaction But O 2 is not always available The use of alternative electron acceptors Anaerobic respiration
Nitrate respiration Utilised by bacteria at unaerobic conditions Dissimilative nitrogen reduction (nitrogen is reduced to produce energy, not to produce organic nitrogen compounds) Important for the nitrogen cycle (process of denitrification the production of elementary N2 from nitrate or nitrite
Biochemistry of Nitrate Respiration Pseudomonas E. coli
Nitrate respiration (E. coli) e - donor e - donor e - donor e - donor e - acceptor
Nitrate respiration (Pseudomonas) e - donor e - donor e - donor e - donor e - acceptor
Sulfate/sulfur Respiration Applies some principles as Nitrate respiration e.g. Desulfurmonas, Desulfurvibrio or Archaeoglobus Dissimilative sulfate reduction Use H 2 or organic carbon sources Only some sulfur-reducing bacteria can oxidise acetate Use acetyl-coa pathway, not Krebs cycle
Sulfate respiration Problem: SO 4 2- is a poor electron acceptor and therefore has to be activated by ATP e - donor e - donor e - acceptor
The Biochemistry of Sulfate/sulfur Respiration
CO 2 respiration e - donor e - acceptor e - acceptor
Acetogenesis Carbonate Respiration the Use of CO 2 as Electron Acceptor CO 2 is common and abundant in anaerobic habitates popular electron acceptor (under anaerobic conditions) Utilises acetyl-coa pathway of CO 2 fixation Typical pathway to fix CO 2 by anaerobes
The Acetyl-CoA Pathway
Methanogenesis By methanogenic bacteria Archaea E.g. in the rumen of cattle, swamps, sediments of lakes and oceans Major green house gas (30x stronger than CO 2 CO 2 + 4H 2 CH 4 + 2H 2 O
The Biochemistry of Methanogenesis
Methanogenesis from Methanol and Acetate
Other Forms of Anaerobic Respiration Proton respiration by Pyrococcus furiosus, the mother of all respirations when life developed?
The carbon cycle in the light of fermentation and respiration
Chemolithotrophy
Chemolithotrophy Organisms that obtain their energy for oxidation of inorganic compounds are called chemolithotrophs
Forms of Chemolithotrophy Many bacteria and archaea Usually autotroph when living on H 2 Fix CO 2 by Calvin cycle Often facultative chemolithoautotroph Prefer e.g. glucose if available Hydrogen Bacteria
Hydrogen bacteria e - donor e - acceptor
Forms of Chemolithotrophy Sulfur Bacteria Oxidation of hydrogen sulfide (H 2 S), elementary sulfur (S) or thiosulfate (S 2 O 3 2- ) to sulfate (SO 4 2- ) Wide-spread among bacteria (e.g. Beggatonia) and archaea (e.g. Sulfolobus spp.) Occurs in stages: Either separate enzymatic steps Or Sox complex (oxidises H 2 S to SO 4 2- in one step)
e - donor Sulfur bacteria e - donor e - donor e - acceptor
Forms of Chemolithotrophy Iron Oxidising Bacteria Many bacteria Acidophiles such as Acidothiobacillus ferrooxidans or Leptospririllum ferrooxidans At the interphase of anaerobic and aerobic conditions, e.g. Gallionella ferruginea or Sphaerotilus natans Form brown deposits of ferric iron
The Biochemistry of Chemolithotrophic iron oxidation Fe 2+ oxidises spontaneously to Fe 3+ in the presence of oxygen at ph > 1 Iron oxidisers live Either at very low ph (<1; extreme acidophiles) Or at the interphase between anaerobic and aerobic conditions
iron bacteria e - donor e - acceptor
Forms of Chemolithotrophy Nitrification Oxidation of ammonia (NH 3 ) and nitrite (NO 2- ) to nitrate (NO 3- ) By specialised bacteria (rarely archaea) Two groups: One group oxidises ammonia to nitrite (e.g. Nitrosomonas spp.) The other group oxidises (e.g. Nitrobacter) nitrite to nitrate Autotrophs Using Calvin cycle Requires reverse electron flow to reduce NAD + to form NADH for anabolism
nitrifying bacteria reverse e - flow e - donor e - acceptor
The Biochemistry of Nitrification
Anammox (anoxic ammonium oxidation) Combines nitrification and denitrification: NH 4+ + NO 2- N 2 + 2H 2 O By members of the Planctomyces group of eubacteria (e.g. Brocadia anammoxidans) Lack peptidoglycan Have intracellular membraneenclosed compartments inside the cell In case of anammox, the anammoxisome Strict autotrophs (acetyl-coa pathway)
The Redox Tower Brock Biology of Microorganisms, 13th ed.
Phototrophy
Forms of Phototrophy
Chlorophylls and Bacteriochlorophylls Chlorophylls cyanobacteria and all eukaryotic phototrophs (algae and green plants) Bacteriochlorophylls anoxic phototrophic bacteria
Different Groups of Phototroph Bacteria Contain Various Bacteriochlorophylls
Other accessory Pigments Carotenoids and Phycobilliproteins
Anoxygenic Photosynthesis By bacteria that use electron donors other than H 2 O for the autotrophic fixation of CO 2 : H 2 S, S, S 2 O 3 2-, NO 2- etc. 5 groups of bacteria: Proteobacteria (purple bacteria, e.g. Rhodobacter) Green sulfur bacteria (e.g. Chlorobium) Green non-sulfur bacteria (e.g. Chloroflexus) Gram-positive Helicobacteria Acidobacteria
Purple Bacteria Photosynthetic electron flow generates protomotoric force ATP synthesis by photophosphorylation Autotroph NAD(P)H production requires reverse electron flow Use mainly H 2 S as electron donor
Purple Bacteria Cytoplasmic membrane surface increased by invagination Membran vesicles or stacks
Purple Bacteria
Green Sulfur Bacteria Optimised for low light conditions Large light harvesting complexes: chlorosomes Prefer H 2 S as electron donors Reduce ferrodoxin Can produce NADH directly
Green Sulfur Bacteria
Comparison of Electron in Different Anoxygenic Phototrophs
Oxigenic Photosynthesis Utilises two different Photosystems Z scheme H 2 O as electron donor Produces NAD(P)H and protomotoric force (ATP) at the same time Autotroph (Calvin cycle) 2 groups: Cyanobacteria (chlorophyll a) Prochlorophytes (chlorophylls a and b)
The Chloroplast
Ways to Fix CO2
Calvin Cycle Reversion of the Pentose Phosphate Pathway Ribulose bisphosphate carboxylase (RubisCO) as key enzyme Most widely distributed in nature
Reverse Citric Acid Cycle: Green sulfur bacteria The origin of the Krebs cycle? Hydroxypropionate Pathway: Green non-sulfur bacteria Possible the most anchient way to fix CO 2 Operational in many archaic groups of bacteria and archaea
Nitrogenase and N2 Fixation The Formation of NH 3 from elementary N 2 Performed by many groups of bacteria
The Biochemistry of N 2 Fixation Dixon & Kahn (2004) Nature Reviews Microbiology 2, 621-631
Nitrogenase and N 2 Fixation Nitrogenase is extremely sensitive to O 2 Protection against O 2 Slime High O 2 consuption Leghemoglobin in symbionts Alternative nitrogenases with vanadium or only iron in case that molybdenium is not available
Nitrogen fixation has been invented twice:
The Nitrogen Cycle