Part 2: Lithotrophic microorganisms Flashcards
What is a lithotrophic organism?
An organisms that oxidises inorganic material and transfers consequent electrons.
In what way do lithotrophs support the rest of the foodchain?
Lithotrophs facilitate recycling of organic material to allow the foodchain to continue - otherwise photosynthesis would not be possible.
What are the 4 most important physiological groups of lithotrophs?
1) Phototrophs - oxidise water to 02
2) Nitrifiers - oxidise ammonia
3) Sulphur oxidisers
4) Iron (and other metal) oxidisers
What key system to lithotrophic aerobes have in common with organotrophic aerobes?
They have a respiratory chain.
How are lithotrophic and heterotrophic organisms linked?
Lithotrophs close biogeochemical cycles, allowing heterotrophic processes to continue.
e.g. lithotrophic nitrifiers convert ammonium to nitrate.
What proportion of oxygen consumption in sediments is due to lithotrophic processes?
50%, although actual lithotroph numbers are low.
How are oxidised metals converted to less soluble reduced metals?
Bacterial metal reduction - an anaerobic heterotrophic process occuring only without O2. A suitable electron donor must be present (e.g. hydrogen, O2).
What are the most/least favourable electron acceptor pairs, and which will be utilised first?
Most: O2 –> H20 (+820 mV)
Least: SO4(2-) –>HS- (-218 mV)
- O2 will be utilised first as it is offers the greatest energy yield.
In what way are lithotrophic organisms limited in their use of electrons?
Electrons cannot be used for both respiration and biomass. Therefore any electrons used in O2 production are lost for ATP formation
Why is sulphide oxidation ,most preferable for chemolithotrophs?
Electrons flow from -ve to +ve redox potential, but to fix CO2, electrons must be at the NADPH level (-320 mV). This costs energy (ATP) to push them toward the -ve potential. Therefore a more electronegative donor is preferable (closer to NADPH level) - the most electronegative is sulphide oxidation (-218 mV)!
What are the two stages of the nitrate cycle, and what organisms are involved in each?
Stage 1 - nitrosofication of ammonia to nitrite (e.g. Nitrosomonas europaea)
Stage 2 - nitrification of nitrite to nitrate (e.g. nitrobacter winogradskyii)
Why are nitrifying bacteria important in most environments?
Degradation of biomass produces ammonium which is a potent fish toxin and can cause eutrophication. Nitrifying bacteria remove ammonia to produce less harmful nitrate.
What are the two stages of the nitrogen cycle?
Stage 1 - oxidation of sulphate to sulphur
Stage 2 - oxidation of sulphur to sulphate
e.g. Thiobacillus spp.
In what environments have non-sulphate oxidising bacteria been found to oxidise sulphate?
Deep sea environments where organics are scarce - e.g. Urania basin.
