Test II Flashcards
1a. Bacteria play key roles in the biogeochemical cycling of nitrogen and sulfur. Describe in detail the individual redox reactions, their associated biochemical pathways, and microorganisms involved in either the nitrogen or sulfur cycle.
5 key steps: Nitrification, Denitrification, N2 Fixation, Ammonification, Anommox.
Nitrogen fixation
- Energy intensive process that produces ammonia (NH3)
- Inhibited by NH3, carried out under anaerobic or oxygen limited conditions.
- In soil, mainly by bacteria associated with nodules on the roots of legumes (25 % of total nitrogen fixed)
- In aquatic and marine environments, predominantly cyanobacteria (35% of total nitrogen fixed).
- All nitrogen fixing archaea are methanogens
- Catalyzed by nitrogenase, a two-part enzyme complex: Dinitrogenase contains two copies of FeMo-co, dinitrogenase reductase contains iron.
- The enzyme is inhibited by oxygen. The structure contains both Fe and S. They are all highly reactive so if exposed to oxygen, it will destroy them. Nitrogenase is protected from O2 in aerobic nitrogen fixers.
-The nitrogen triple bond makes nitrogen extremely inert. Nitrogen fixation is a very energy intensive process. 8 e- are consumed but only 6 e- are transferred t o nitrogen atoms.
-Electrons are supplied by dinitrogenase reductase to dinitrogenase one at a time. Two ATPs are hydrolyzed to supply one electron.
Pyruvate donates electrons to flavodoxin. Flavodoxin reduces dinitrogenase reductase. Electrons are transferred to dinitrogenase one at a time. 2 ATP are consumed per electron.
(N2 → HN=NH → H2N-NH2 → NH3)
-Diazotrophs: microorganism that fix N2. Nitrogenase is highly conserved. Free living anaerobes. Aerobic diazotrophs employ strategies to keep O2 away from Nitrogenase.
Anammox
- Anammox stands for anaerobic ammonium oxidation. (NO2- + NH4+ → N2 +2H2O). -NO2- acts as the e- acceptor and is the product of aerobic ammonia oxidation (nitrification).
- An example of a microbe that uses this process is: Brocadia anammoxidans. An “organelle” within the cell called anammoxosome contains a strong reductane: N2H4. It lacks the Calvin cycle enzymes and instead uses the acetyl-CoA pathway to fix CO2.
Ammonification and ammonium assimilation
Ammonification uses organic-N and produces NH4+. Many microbes can do this. Ammonium incorporated into cellular components (e.g. amino acids, purines, pyrimidines).
Nitrogen assimilation is the formation of organic nitrogen compounds (e.g. amino acids) form inorganic nitrogen compounds present in the environment.
C:N if C is 20 times more, ammonium assimilation is occurring. If C is less, ammonification is occurring.
Nitrification
NH4+ → NO2- → NO3- (oxidative reactions coupled with oxygen)
-Carried out in 2 steps by two kind of nitrifiers: ammonium oxidizers and nitrite oxidizers.
-Net energy producing reactions carried out by Chemolithotrophic (and mostly autotrophic) bacteria and archaea.
-Some heterotrophic fungi and bacteria can also perform nitrification, although no energy is produced.
Nitrosifying bacteria
1. NH3 + O2 + 2e- + 2H+ → NH2OH + H2O
Carried out by ammonia monooxygenase (AMO). Produces hydroxylamine (NH2OH). Requires two electrons.
- NH2OH + H2O + 1/3 O2 → NO2- + 2H2O + H+
Carried out by hydroxylamine oxidoreductase (HAO), Produces nitrate (NO2). Generates 4 electrons.
Sum: NH3 + 1 ½ O2 → NO2- + H2O
Only 2 electrons are actually generated.
Nitrifying bacteria
NO2- + ½ O2 → NO3-
-carried out by nitrite oxidoreductase.
-Very short ETC
-Generates a PMF through cytochrome aa3 which ultimately drives ATP synthesis.
-CO2 is fixed using the Calvin cycle.
-All nitrifying bacteria are Proteobacteria except Nitrospira which forms its own phylum.
-Wide spread in soil and water, particularly environments rich in ammonia (from ammonification)
Denitrification
NO3- → N2
- Nitrite used as terminal electron acceptor.
- occurs under microaerophilic or anaerobic conditions
- Primary type of dissimilatory nitrate reduction in soil.
- Not inhibited by NH4+. Reduction reactions.
nitrate (NO3-) --> nitrite (NO2-) - nitrate reductase. nitrite --> nitric oxide (NO) -nitrite reductase. nitric oxide --> nitrous oxide (N2O) -nitric oxide reductase. Nitrous oxide--> dinitrogen (N2) nitrous oxide reductase.
- The 4 enzymes used are sensitive to oxygen and are inter-regulated. Nitrate is required for the full expression of the enzymes. N2O is the main product under high O2 conc or low NO3- conc.
- This process is mostly carried out by respiratory heterotrophs.
2a. Discuss the metabolic and phylogenetic diversity of nitrification. What are the roles of different groups of microorganisms involved, and what are the key enzymes involved? Explain why many nitrite oxidizers are chemoorganotrophs from the perspective of energetics.
NH4- → NO2- → NO3-
-Nitrification is the oxidation of ammonia. Oxidative reaction coupled with oxygen.
- Carried out in two steps by two kinds of nitrifiers: ammonium oxidizers and nitrate oxidizers.
- Net energy producing reactions carried out by Chemolithotrophic and mostly autotrophic bacteria and archaea
- Some heterotrophic fungi and bacteria can also perform nitrification although no energy is produced.
- Nitrification occurs at the membrane.
Nitrosifying bacteria
Nitrifying bacteria
Nitrosifying bacteria
Nitrifying bacteria
Nitrosifying bacteria
1. NH3 + O2 + 2e- + 2H+ → NH2OH + H2O
Carried out by ammonia monooxygenase (AMO). Produces hydroxylamine (NH2OH). Requires two electrons.
- NH2OH + H2O + 1/3 O2 → NO2- + 2H2O + H+
Carried out by hydroxylamine oxidoreductase (HAO), Produces nitrate (NO2). Generates 4 electrons.
Sum: NH3 + 1 ½ O2 → NO2- + H2O
Only 2 electrons are actually generated.
Nitrifying bacteria
NO2- + ½ O2 → NO3-
-carried out by nitrite oxidoreductase.
-Very short ETC
-Generates a PMF through cytochrome aa3 which ultimately drives ATP synthesis.
-CO2 is fixed using the Calvin cycle.
-All nitrifying bacteria are Proteobacteria except Nitrospira which forms its own phylum.
-Wide spread in soil and water, particularly environments rich in ammonia (from ammonification)
2a. Explain why many nitrite oxidizers are chemoorganotrophs from the perspective of energetics.
- more favourable energetically to obtain the energy from the oxidation of reduced compounds.
- They don’t produce enough energy for themselves due to the small transport chain. -They also use the Calvin cycle to fix CO2. -This puts severe energy constraints on them.
- They have low growth yield due to this.
- All nitrifying bacteria are Proteobacteria except for Nitrospira.
4a. Discuss the biochemistry of sulfur oxidation, the unusual ecology of sulfur
oxidizing bacteria, and at least one example of strategies used by sulfur oxidizers in non-acidic environments to obtain inorganic nutrients.
- Oxidation of hydrogen sulfide (H2S), elemental sulfur (S0) or thiosulfate (S2O32-) to ultimately sulfate (SO42-l
- Sulfide (HS-) is oxidized to sulfite (SO32-) through the transfer of 6 e-
-If starting from elemental sulfur (S0) first reduce it to sulfide before oxidizing it to sulfite. S2O32- is first split into S0 and SO32-
-Sulfite is eventually oxidized to sulfate (SO42-). Sulfite oxidase is the most common pathway. A few chemolithotrophs use the APS reductase in reverse.
-The Sox system oxidizes sulfide directly to sulfate
-Chemolithotrophic sulfur oxidation (aerobic) generally tolerates and often requires low pH.
-Photoautotrophic sulfur oxidation (anaerobic and Anoxygenic). Limited to green and purple sulfur bacteria.
CO2 + H2S → S0 + fixed carbon.
4a. The unusual ecology of sulfur
oxidizing bacteria
The unusual ecology of sulfur oxidizing bacteria is that sulfide reacts with oxygen rapidly but not instantaneous. Therefor these organisms have evolved to somehow reconcile the simultaneous need for sulfide and oxygen. Sulfur oxidizers live in environments where they need both oxygen and H2S. This is unusual as these two things normally react spontaneously. The fact that these organisms live where they don’t react together is unusual.
4a. Discuss the biochemistry of sulfur oxidation, the unusual ecology of sulfur
oxidizing bacteria, and at least one example of strategies used by sulfur oxidizers in non-acidic environments to obtain inorganic nutrients.
Examples
Thiothrix
- use filaments to hold position in fast flowing water rich in O2 and H2S.
- Finds a place where you have mixing occurring. Where water flows, your going to have oxygen, disturbing the sediment also releases H2S. Uses filaments to hold onto stable places. Can then use the oxygen.
4a. Discuss the biochemistry of sulfur oxidation, the unusual ecology of sulfur
oxidizing bacteria, and at least one example of strategies used by sulfur oxidizers in non-acidic environments to obtain inorganic nutrients.
Examples
Desulfobaulbaceae
-Filamentous multicellular bacteria (aka cable bacteria)
-Centimeter long structures containing thousands of Bacteria inside an outer membrane,
-Electrons obtained from sulfide oxidation are transported via ‘bacterial micro cable’ to the surface for oxygen reduction.
-Half reactions occur more than a centimeter apart.
-Also capable of using nitrate and nitrate as electron acceptors.
They carry sulfur reduction at the bottom. Can dump electrons onto oxygen. Just need to dump electrons for the reaction to continue.
5a. Describe the conditions that lead to the self-propagating oxidation of pyrite, how the process contributes to the formation of acid mine drainage, and the ecological significance of acid mine drainage.
-Pyrite (FES2) is one of the most common forms of iron. Present in bituminous coals and metal ores.
A combination of chemical and bacterial oxidation of FeS2 leads to acidification
- FeS2 is oxidized to O2, generating HS, which is then oxidized to SO42-
- Biological oxidation of Fe2+ to Fe3+
- Fe3+ spontaneously reacts with FeS2 and produces more SO42-
In nature in terms of mining, it is very rare to contain a pure metal or a very specific metal. One of the most common substance in mining in terms of metal is Pyrite (FeS2). Elemental metal iron spontaneously reacts with sulphur that results to pyrite. This is one of the most common form of iron. Digging deeper into a mine or metal mines, you will find a combination of chemical and bacteria oxidation of pyrite can lead to acidification of the environment.
5a. Describe the conditions that lead to the self-propagating oxidation of pyrite, how the process contributes to the formation of acid mine drainage, and the ecological significance of acid mine drainage.
Propagation cycle
Pyrite (FeS2) oxidized to Ferrous oxide (FeO) then ferrous oxidise can be further oxidised by a bacteria or spontaneously to Ferrous ion.
- At this point, the environment will be acidified because of the sulphuric acid (2SO42- + H+).
- The ferrous ion is stable and this spontaneously react to ferrous oxide.
- The initiation of this process is oxygen dependent. However, the actual propagation cycle is NOT oxygen dependent because the process has Ferrous oxide reacting as the reductant.
- Cycle becomes self propagating. Don’t need an electron acceptor at this point.
5a. Describe the conditions that lead to the self-propagating oxidation of pyrite, how the process contributes to the formation of acid mine drainage, and the ecological significance of acid mine drainage.
Acid mine drainage
Acid mine drainage:
FeS2 + 14 Fe3+ + 8H2O → 15 Fe2+ + 2SO42- + 16 H+
-self propagating process
The problem with this production is when it rains or when ground water seeping through. This reactions gets intiated.
Water plays an important role in this process as once it slips through in coal-mining operation, the self-propagating cycle gets initiated.
- Once the process is initiated, it does not require further addition of oxygen and water. -The process results in acidifying the environment (pH <1).
- This pH 1 (acidified environment) dissolves heavy metals.
- Leaking takes place of the heavy metals this results affects the surrounding the fresh water system where the mine is operating.
- Ferroplasma is an Archaeon that acts as an indicator when there is an acid mine drainage problem as it grows from pH O in 50 degrees.
A major problem in all surface coal mining operations
- pH <1
- dissolves heavy metals
- degrades water quality in rivers and lakes
6a. Describe the physiology of microbial nanowires as currently understood and the metabolic advantages possessed by microorganisms that have microbial nanowires.
Electrically conductive appendages produced by certain Fe3+ reducing bacteria, e.g. Genobacter and Shewanella sp
- Useful in environments depleted of electron acceptors.
- Transfer electrons to insoluble materials e.g. ferric oxides.
- In Shewanella: extensions of outer membrane that conduct through cytoplasm
- In Geobacter: modified pili
- Electrons shuttling by nanowires can occur over large distances. Electron transfer across biofilm layers. Sheaths are used to translocate the electrons.
- Produced by Shewanella under oxygen-deprived conditions. Conductivity similar to semiconductors.
- Use nanowire to obtain electrons from electron donors.
- Only want to do this if you don’t have access to good terminal electron acceptors
- This organism act as the terminal electron acceptor for other organisms
- Get electrons from other organisms. As electrons go through the e- transport chain this makes a PMF and so ATP.
- Once you make a circuit where electrons can flow, can tap into this. This makes a battery.
- Can steal these electrons and use for fuel cells. These organisms form the basis of microbial fuel cells. Generate electrical currents by collecting electrons from microbial oxidation of toxic or waste material (e.g. landfills) via microbial nanowires.
7a. What is the defining characteristic of halophiles? Describe physiological adaptations in halophiles specifically associated with this characteristic. What are the characteristics of osmophiles and xerophiles, and what are the key features of compatible solutes?
Halophiles have a requirement for NaCl in order for them to grow. They require 1-12 % NaCL and extreme halophiles require >9 % and grow at up to 32 % NaCl. This cannot be replaced by other salts e.g. K+, Mg2+
- Halotolerant microorganisms grow best in the absence of solutes
- Most extreme halophiles are Archaea. Nearly all are obligate aerobes.
Halobacterium salinarum, an archaeon, -requires Na+ and K+. Na+ is required on the outside of its membrane to balance the negatively charged proteins that are next to the membrane inside the cell.
- It stabilises the cell wall containing glycoproteins rich with negatively charged amino acids.
- Lower conc. of Na+ causes the negatively charged proteins to repel each other. -Proteins in the cytoplasm are acidic so it requires K+ for stability and activity.
- This has the effect of balancing osmotic pressure in terms of countering Na+ on the outside of the cell.
Bacteriorhodopsin is a mechanism found in many halophilic archaea that facilitates phototrophic generation of ATP under anoxic conditions (not photosynthesis).
-It absorbs light energy and uses it to pump a proton across the cytoplasmic membrane. -They are found as red and orange carotenoids, a similar structure to the rhodopsin found in the human eye. In H. salinarum, the mechanism is linked to Na+ and H+ pumping, using it to maintain the balance between Na+ and K+. An Na+ - H+ antiport system achieves this.
7a. What is the defining characteristic of halophiles? Describe physiological adaptations in halophiles specifically associated with this characteristic.
What are the characteristics of osmophiles and xerophiles?
Osmophiles
-Not the same as halophiles. Both groups are adapted to high osmolarity in the environment . Osmophiles do not require high osmolarity
They are adapted to high solute concentrations. Glycerol is the primary compatible solute. Cause spoilage in high sugar food items. Generally not pathogenic
Xenophiles
-Organisms adapted to very low moisture content (and possibly high osmolarity)
7a. What is the defining characteristic of halophiles? Describe physiological adaptations in halophiles specifically associated with this characteristic. What are the characteristics of osmophiles and xerophiles,
Key features of compatible solutes?
Compatible solutes are needed to maintain a positive water (slight positive osmotic pressure) so that they have access to water. —Must have compatible solutes to offset the high salt concentration outside of the cell membrane.
- These solutes must be acquired or synthesised in large amounts to have the effect and not interfere with cellular processes.
- Examples in halophiles include glycine, betadine and glycerol.
8a. Describe in detail at least four mechanisms commonly adopted by thermophiles to overcome the challenges of surviving at high temperatures.
Prokaryotes are more thermal tolerant that eukaryotes. Archaea are more thermal tolerant than Bacteria. There is a clear upper limit temperature for photosynthesis.
- Heat stable enzymes that function better at high temperatures
- Stabilization of proteins
- DNA stability
- Ribosomal RNA tRNA stability
- Cytoplasmic membrane stability
8a. Describe in detail at least four mechanisms commonly adopted by thermophiles to overcome the challenges of surviving at high temperatures.
- Heat stable enzymes that function better at high temperatures
- Stabilization of proteins
- DNA stability
Heat stable enzymes that function better at high temperatures
- Increased ionic bonds between basic and acidic amino acids
- Greater hydrophobicity in the interiors.
- Increased disulfide bonds between cysteine residues
Stabilization of proteins
- Chaperonins (thermosome in Archaea) help refold partially denatured proteins
- Intracellular solutes (e.g. diglycerol phosphate and mannosylglycerate) help stabilize proteins
- Increases the temperature at which organisms can survive but not necessarily grow.
DNA stability
- Increased intracellular solutes reduce depurination and depypyrimidization
- Reverse DNA gyrase introduced positive supercoils into the DNA of hyperthermophiles
- Histones in Euryarchaeota compact DNA into nucleosome like structures and prevent DNA strains from separating
8a. Describe in detail at least four mechanisms commonly adopted by thermophiles to overcome the challenges of surviving at high temperatures.
- Ribosomal RNA tRNA stability
- Cytoplasmic membrane stability
Ribosomal RNA tRNA stability
- Higher proportion of GC nucleotides in the rRNA and tRNA of hyperthermophiles
- G-C pairs are mores stable that A-U pairs, allowing rRNA to maintain secondary structures
Cytoplasmic membrane stability
- More long chained (e.g. higher melting point) and saturated (higher hydrophobicity) fatty acids in lipid bilayer membranes
- Lipid monolayer membranes in practically all hyperthemophilic archaea
9a. Describe in detail three environmental factors that influence known upper temperature limits for microbial life in various habitats.
Hyperthermophiles are defined as having their optimal growth >85 degrees.
- Archaea can grow at 122 C. Many of the species grow optimally above 100 C.
- Chemolithotrophic or chemoorganotrophic
Water boils at 100 C.
Requires nucleation points. These environments have been hot so long (thousands of years) that their nucleation points are gone; if you were to drop a pebble which has lots of nucleation points, the water would boil up high.
-High pressure is another environmental factor that influences the upper temperature limit.
-In high pressure environments such as subsurface aquifers (>250 C) and deep sea hydrothermal vents (up to 400 C).
-Another environmental factor is the interaction between temperature and pH. Majority of hyperthermophiles at very high temperatures at a near neutral pH.
-If you have an acidic environment, e.g. pH 2, 80 C is the temp limit: heat and acidity is a lethal combination for microorganisms.
-If you look at acidic hot pools above 80oC, they are mostly likely sterile as we are not aware of any microorganism that can survive high T and low pH.
Macromolecules have been detected in hydrothermal vent water at 150 C. This tells us that if these types of macromolecules can be found, then maybe life is possible.
9a. Describe in detail three environmental factors that influence known upper temperature limits for microbial life in various habitats,
Three examples of why life is unlikely to be present at supercritical (e.g., >250°C) temperatures.
However, at superheated hydrothermal vent water (>250oC), life is unlikely to be present because they contain no DNA, RNA or protein which are molecules essential for life. These are unable to exist at such high temperatures as they denature, therefore life cannot exist.
Biochemical issues at super critical temperatures
- ATP is degraded almost instantly at 150 C
- Amidation (spontaneous cleaving of peptide bonds) occurs above 130 C. Proteins will completely break.
- Critical chemical reactions maybe unfavourable (or become spontaneous) at higher temperatures.
10a. Explain the difficulties encountered by acidophiles and list at least two examples of how these difficulties are overcome.
What evidence suggests that the intracellular pH of acidophiles is close to pH 7.0?
Acidophiles live in environments below pH 7. There is a high number of H+ outside the cell. Natural proton motive force: large pH gradient (up to 5 orders of magnitude) across the cytoplasmic membrane.
-Microbes must maintain intracellular pH homeostasis. Protons also leak through cytoplasmic membrane.
Internal pH must remain near neutrality. pH 5-9
- DNA is acid labile
- RNA is alkaline labile
- RNA will breakdown in alkaline environments while DNA will break down in acidic environments.
- Intracellular enzymes have a pH optima near 7 and denature at extracellular pH levels. Physiological adaptations to deal with extreme pH.
10a. Explain the difficulties encountered by acidophiles and list at least two examples of how these difficulties are overcome. What evidence suggests that the intracellular pH of acidophiles is close to pH 7.0?
Adaptations of acidophily:
Examples of how these difficulties are overcome
Cytoplasmic membrane requires a high [H+] to maintain stability. The massive concentration of protons on the outside keeps the membrane together.
Active solutions -Proton efflux systems (requires energy) -Using electrons generated by oxidative phosphorylation and oxygen to convert H+ to H2O. -Reverse membrane potential Pumps protons out but require energy.
Passive solutions
-Reduce membrane permeability (e,g, tetraether lipids)
-Coating the cell wall with positively charged proteins
-Cytoplasmic buffering molecules
Repulsion membrane potential-the repulsion between the positively charged membrane keeps the protons away at a distance making it less likely they come in the cell.
Secondary adaptations
-abundance of secondary transporters that use PMF to transport nutrients
-repairing acidity-induced damages to DNA and protein.
Use a lot of secondary transporters that use the PMF to transport nutrients. Most organisms make a PMF and then use it, they don’t waste it. Acidophiles have an influx of protons so they might as well use it. They couple the transport of nutrients with the PMF and they just deal with the influx of protons.
There is no ‘universal’ adaptation to acidophily.
11a. Explain the difficulties encountered by alkaliphiles and list at least two examples of how these difficulties are overcome.
What evidence suggests that the intracellular pH of alkaliphiles is close to pH 7.0?
- They have a very high concentration of OH- around the cells.
- OH- spontaneously combines with H+ to form H2O. Makes it hard for the organisms to form a PMF for the production of energy (ATP)
- Natural reverse proton gradient.
To overcome this, they use a sodium motive force to generate ATP and drive transporters. Alkaliphile habitats are often rich in Na+.
-Some alkaliphiles can use a PMF to make ATP but the mechanism is unclear. Likely involves keeping proteins extremely close to the outer cytoplasmic membrane and way from OH-.
Other uses for a sodium gradient
- Na+ symports for nutrient transport
- Drive flagella using the Na+ gradient
- how to maintain a Na+ gradient
Active acidification
- Na+/H+ antiporters found in all alkaliphiles.
- If you have an antiporter, pumps in protons with the pumping out of sodium so you can maintain a sodium gradient while acidifying the cytoplasm (RNA is acid labile)
Passive acidification
- Cell wall rich in polymers made of organic acids (e.g. glutamic acid and gluconis acid), which prevents the entry of OH-)
- Higher hexosamine and amino acid content in the peptidoglycan.
- If you have the negatively charged membrane, this repulses the negatively charged OH- ions making it less likely for them to come inside.
11a. Explain the difficulties encountered by alkaliphiles and list at least two examples of how these difficulties are overcome.
What evidence suggests that the intracellular pH of alkaliphiles is close to pH 7.0?
Internal pH must remain near neutral.
- DNA is acid labile
- RNA is alkaline labile
- RNA will breakdown in alkaline environments while DNA will break down in acidic environments.
- Intracellular enzymes have a pH optima near 7 and denature at extracellular pH levels.
12a. What were the conditions in Earth’s oceans four billion years ago? How would the conditions have shaped the dominant microbial metabolism at the time? List one example of those metabolic pathways that we still see in microorganisms today.
Cellular life started about 4 billion years ago. The early oceans were:
- For the most part, Earth was anoxic
- high temperatures
- limited organic carbon as there was no photosynthesis.
- Rich in H2S (from volcanoes) (and FeS), CO2 and H2.
These conditions set boundaries on what microbial life had to be like.
Bacteria and archaea diverged before photosynthesis. Anoxygenic photosynthesis. Cyanobacteria then came, combined with chlorophyll to produce oxygen. This killed a lot of the microbial life. Then came the formation of the ozone layer. Without it, life could not leave the sea as then would be bombarded with UV. So important for life to evolve on land.
12a. What were the conditions in Earth’s oceans four billion years ago?
How would the conditions have shaped the dominant microbial metabolism at the time?
Around 4 billion years ago, microbes would have likely used H2 as electron donor (I,e, fuel).
- It formed spontaneously from H2S and H+ (acid). Have multiple sources of hydrogen and primitive hydrogenase which oxidises hydrogen and passes electrons along to elemental sulfur, this drives substrate level phosphorylation of ATP
- Hydrogen based metabolism requires the fewest proteins so lower barriers to cross when acquiring energy
- Likely reduced S0 (elemental sulfur) as fewer enzymes are needed than sulfate reduction.
This drives oxidative phosphorylation of ATP at primitive ATPase (using primitive PMF). Microbial metabolism had to be autotrophic as there’s no substrate for them to burn apart from hydrogen, and no other carbon source; they produced acetate and methanol.
-There also most likely no biological nitrogen fixation; it a complicated pathway, if there is a low demand for nitrogen then things like lightning that can fix nitrogen is sufficient.
12a. What were the conditions in Earth’s oceans four billion years ago?
List one example of those metabolic pathways that we still see in microorganisms today.
-One example of the metabolic pathways we still see today in microorganisms is H2 metabolism. There are many microorganisms that use H2 as an energy source such as chemolithotropic aerobic H2-oxidising bacteria e.g. Beggiatoa. There are also microorganisms that produce H2 such as purple photosynthetic bacteria.
