-
chemolithotrophy
the oxidation of inorganic electron donors to obtain energy
- ATP synthesis is coupled to oxidation of the inorganic electron donor
- Reducing power is obtained directly from the inorganic compound or from reverse electron transport
-
energetics and carbon flow
- electron transport leading to proton motive force
- energy can be generated from electron transport from electron donors to electron acceptors
-
autotrophs
carbon source is CO2
-
mixotrophs
carbon source is an organic compound
-
energetics of chemolithotrophy
- both electron donor and electron acceptor determine energetics
- difference in reduction potential of the two couples needs to be sufficient to produce ATP - requires ~32 kJ/mol
- DGo’= -nF DEo’
- n= number of electrons
- F= Farraday constant (96.48 kJ/V)
- DEo’=Eo’ of electron acceptor couple minus Eo’ of electron donor couple
-
concept of chemolithotrophy conceived by Winogradsky
- observations of Beggiatoa, colorless sulfur bacteria - large, filamentous, could observe directly:
- only observed these bacteria in H2S-rich springs
- if deprived of H2S, lose sulfur granules, continue to grow
- if H2S then supplied, grow sulfur granules form
- concluded H2S -> S0
- S0 acts as energy source
- S0 is oxidized to sulfate
-
electron flow in sulfur chemolithotrophs
can use standard electron transport system components
-
anaerobic corrosion of iron
- route 1: H2 -> H2S + Fe0 -> FeS(precipitate) + H2(recycled)
- iron loses electrons, acts as donor
route 2: 4Fe 0 + SO 42- + 4H 20 -> FeS + 3Fe 2+ + 80H-
-
hydrogen as inorganic electron donor
- hydrogen-oxidizing chemolithotrophs:
- oxygen as electron acceptor
- anaerobic using something else as electron acceptors
- aerobic H2 bacteria are autotrophs and fix CO2 via Calvin Cycle
- Generation of ATP during H2 oxidation is catalyzed by hydrogenase - oxygen-sensitive, thus grows best under microoxic conditions
can also grow chemoorganotrophically with organic compounds as energy sources - thus are facultative chemotlithotrophs depending on environmental conditions
-
iron bacteria and energy from ferrous ion oxidation*
chemolithotrophs that use ferrous iron (Fe2+) as their sole energy source
only a small amount of energy is available from oxidation of Fe2+ - lots must be oxidized
- under neutral conditions, Fe2+ is oxidized non-biologically
- under acidic conditions Fe2+ is stable and soluble and available to be oxidized
- - most iron-oxidizing bacteria are obligately acidophilic
- "natural" PMF across membrane, so ATP synthesis can occur as long as Fe2+ available - low ATP yield, limited growth
oxidizing ferric iron forming insoluble ferric hydroxide and complex ferrous salts known as " yellow boy"
specialized oxidoreductase: rusticyanin
- some anoxygenic phototrophs oxidize ferrous iron
- uses reverse electron flow
|
|