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| Green Dragon Spring, Yellowstone Credit: National Park Service |
Download Episode (8.1 MB, 8.8 minutes)
Show notes:
Microbe of the episode: Vitreoscilla beggiatoides
News item
Journal Paper:
Amenabar MJ, Shock EL, Roden EE, Peters JW, Boyd ES. 2017. Microbial substrate preference dictated by energy demand rather than supply. Nat Geosci 10:577–581.
Other interesting stories:
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Episode outline:
- Background: Microbes crazy good at using various energy sources
- Metals, minerals, gases, various organic compounds
- Almost anything can either donate or accept electrons to generate energy
- Would expect each microbe to use best sources of energy it can
- But expectations don’t always fit reality
- What’s new: Here, scientists publishing in Nature Geoscience have discovered a species of archaea that prefers to use a weaker source of energy even when a stronger one is available!
- Acidianus DS80, thermoacidophile from Green Dragon Spring in Yellowstone National Park
- 3.1 pH, 78C
- Can take electrons from sulfur or hydrogen gas and transfer to sulfur or ferric iron
- Then use energy to fix CO2
- Chemically, most energy from H2-Fe, then S-Fe, and least from H2-S
- Like eating lettuce vs. steak or pasta
- Or nuclear power vs. burning coal; much higher energy density
- Methods: Doubling time was similar for each energy source
- CO2 taken up also similar with H2+S or S+Fe, but 2x less with H2+Fe
- And cells larger with H2+S
- So used up more potential energy for same CO2 gain with Fe vs. H2+S, 8x more
- Different efficiencies in pathways
- When cells given all 3 elements at once, still seemed to use only H2+S
- Didn’t see excess increase in sulfate ions (produced from sulfur ox)
- Fe reduced but abiotically by H2S from S reduction
- So why preference for lower energy pairing?
- Might depend on machinery required for each pairing
- H2+S has hydrogenase and sulfur reductase with some electron transfer proteins between
- Happens around membrane
- Fe not well known, but cells growing with it make hairlike projections: nanowires
- Used by others to transport electrons far away from cells
- Energy lost in making these nanowires
- Also as heat from resistance in electrical conductance
- So more expensive to use Fe
- Summary: Archaea in hot springs prefer to get their energy by transferring electrons from hydrogen to sulfur, even though more energy is available from a transfer between hydrogen or sulfur to iron, because it seems that using iron is more expensive to the cell
- Applications and implications: More to metabolism than simple theoretical energy in food
- Also consider genetic and machinery requirement costs
- If hard to afford facility to use nuclear power, can’t use it
- Or if can’t digest steak, less-energetic food is better
- Clarifications if necessary: Same in nature/community as in lab?
- Often pairing with microbes with other metabolisms enhances both kinds
- Might make higher-energy pairings more favorable for Acidianus
- What do I think: Wonder how competition affects metabolism preferences of this species
- Maybe other species can utilize iron more effectively, hard for Acidianus to compete
- So it doesn’t try very hard, goes for other energy source
- Need more study to find out if this is the case, or what
- Human takeaway: Sometimes what seems like the most profitable or powerful approach is not always the best
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