L2 - Microbial Metabolism Flashcards
Give two reasons that microbes have evolved to inhabit all ecosystems
- Incredible metabolic diversity
- Adaptive ability
Give the three major classes of metabolism among microbes including the energy source, carbon fixing source and examples of microbes that use that metabolism.
1) Photo(auto)troph
- Light energy
- C from CO2
- E.g. cyanobacteria, some purple + green bacteria
2) Litho(auto)troph
- Energy: inorganic compounds e.g. H2, NO2
- C from CO2
- Some bacteria and many Archaea (e.g. methanotrophs)
3) Heterotroph
- Energy: Organic compounds
- C from organic compounds
- Most bacteria, some Archaea
Define saprotrophy? Which group uses it extensively and why?
Saprotrophy: Use of dead or decaying metter as C source
Extensive in fungi as able to use diversity of C sources, e.g. simple sugar, chitin, cellulose
Outline how fungi digest and take up carbon from decaying matter
1) Digestive enzymes secreted from hyphae tip + digestion compounds
2) Most C sources hydrolysed to simple monomers e.g. by (gluco) amylase for starch and invertase for sucrose
3) Nutrients taken up in sub-apical region of hypha by H+ symport and passive transport
Describe how cellulose specifically is taken up by fungi
1) Hydrolysed by complex enzymes e.g. cellobiohydrolase (CBH)
2) Two cellobiose units (β-glucose molecules) produced
3) β-glucose molecules hydrolysed to glucose monomers by β-glucanase
4) Glucose imported by hexose transporters
Give the only group of fungi that can decompose lignin.
Name and describe the 3 classes of enzymes used to do so
What potential use does this group have?
- Only by white rot fungi e.g. P. chryosporium as large polymer resistant to deposition
1) Lignin peroxidases used (LiPs)
- Haem-containing proteins
- strong oxidants
- degrade large substrate directly using Trp171 residue on outside of protein
2) Manganese Peroxidases (MnPs) used
- Haem containing proteins
- strong oxidants
- No residue = can’t hydrolyse directly
- Catalyse oxidation of Mn(II) to Mn(III) which diffuses away in oxalate complex to oxidise substrate
3) Cytochrome P450 monooxygenases
- Catalyse wide range of reactions for wide range of substrates
Broad specificity and strong oxidising of enzymes = bioremediation potential
What is a methanogen?
Give an example of where methanogens play an important role in the carbon cycle
Expand upon one of these examples
- An organism that produces methane
- Significant roles in carbon cycle in anoxic conditions + stomachs of ruminant herbivores
- Rumen is anoxic w/ syntrophic community of bacteria and archaea
Give examples of 5 of the microbe classes seen in the rumen
- Cellulose decomposers (bacteria), produce CO2 as one (of many) byproducts
- Starch decomposers (bacteria)
- Lactate decomposers (bacteria)
- Succinate decomposers (bacteria), produce CO2
- Methanogens e.g. Methanomicrobium mobile (Archaea)
Describe the overall function of methanogenesis.
Sketch the relevant diagram for methanogenesis
How can it be observed that methanogenesis is occuring
- Reducing process using e- from H2
- Generates proton motive force, makes ATP (anaerobic respiration)
- Produces methane
- See diagram on pg 11
- F420 enzyme is fluorescent
Why are methanogens also important for other types of bacteria
- H2 produced from fermentation but can inhibit growth of some fermenting bacteria
- Methanogenesis removes H2 - syntrophy
- Important in landfill sites
Describe an example syntrophy involving fermenting bacteria and methanogens. Give 6 steps OR draw the relevant diagram
Guts of wood eating termites:
1) Termites chew wood
2) Termites digest cellulose into fragments via endoglucanase from salivary glands
3) Fragments engulfed by protist (eukaryote)
4) Cellulose digested to glucose monomers, then fermented to acetate, ATP and H2
5) H2 used by methanogens for CH4
6) H2 also transferred to acetogens and converted to acetate, used by termite for metabolism
- See diagram on pg 13
What are methanotrophs?
Sketch the relevant diagram for methane catabolism
- Organisms that use methane as electron donors for energy generation
- See diagram on pg 13
(Most important enzyme is Methane Monooxygenase (MMO))
Give a case study where the ecological significance of methanotrophs was demonstrated
Deep Water Horizon Accident
- big oil spill
- Only 0.01% of CH4 released went into atmosphere
- 16S rRNA surveys revealed significant growth of methanotrophic bacteria near spill
- Oil-degrading bacteria also enriched, degrading oil quicker than predictions
