Early Microbial metabolic stragegies Flashcards
(30 cards)
what type of organism is at the deepest branches of the tree of life?
thermophilic and hyperthermophilic autotrophs
(survive in hot temperatures)
what PEDs and TEAs do thermo and hyperthermophilic bacteria use and for what mechanism
H2 as PED
NO3-, O2, S, Fe(III) as TEAS
to fix CO2
what are common PEDs and TEAs for both early bacteria and prokaryotes
H2 as PED
S as TEA
what metabolism do we think earliest life used
chemolithoautotrophy
(using chemical energy to fixing inorganic carbon and using inorganic carbon as a TEA)
what was adaptive metabolism developed to consume complex carbon formed by earliest life?
fermenters - to use of complex organic carbons
What is a problem with fermentation?
Does not oxidize organic matter completely
What was a likely TEA allowing for fully oxidized products of fermentation?
elemental sulfur and sulfate
what type of organism likely evolved to consume products of fermentation?
anoxic respirers
When did BIFs form?
3.5 Ga to 1.8 Ga
What is a BIF?
Banded Iron Formation
sedimentary rock of alternating iron oxide shale (dark) and chert (red)
Generally accepted ideas about BIF formation
1- iron is of hydrothermal formation
2- ferric iron (iron III) is unsoluble so precipitates out easily, but is indicative of oxidizing conditions
3- for iron to be transported, it must be iron II, which is soluble and indicative of reducing conditions
4- thus redox chem plays role
dilemma with BIF formatin
no microbial evidence, even though that would be most obvious manner to flip between iron II and iron III
Conventional theory of BIF formation
formed in sea water as a result of oxygen released by photosynthetic cyanobacteria which would oxidize Fe2+ into Fe3+ and it would precipitate out, something would block the cyanobacteria from metabolizing which would stop the fe2+ from oxidizing, leaving a layer of chert
Protoenzyme theory of BIF formation
a primitive photosynthetic bacteria (predecessor to cyanobacteria) produced O2 as a waste product but there was no mechanism to deal with it. Fe2+ would be protoenzyme that reduced O2 and thereby reduced toxicity for the bacteria. A cyclic process that controlled the hydrothermal Fe2+ would explain the layering.
who proposed protoenzyme theory and when
Cloud, 1965
Gallionella BIF formation theory
chemolithoautotroph that uses iron(II) as its energy source, uses O2, so aerobic but can happen in low O2 environments. This is 60 times faster than abiotic oxidation of iron (II). An ocean with limited photosynthetic oxygen would explain the cyclic nature.
who proposed Gallionella theory and when
Holm, 1989
Anoxygenic Photosynthesis BIF formation theory
purple sulfur bacteria coupling Fe2+ oxidation with reduction of CO2 during anoxygenic photosynthesis which explains iron deposition before free oxygen was available
Surface adsorption BIF formation theory
passive process involving surface binding of ferrous iron or aqueous ferric species to microbial surfaces. This would allow ferrous iron to be transported to oxygenated environments and reduces activation energy for precipitation so mineralization would occur more rapidly
Key significant outcome of the oxidation of earth, why?
production of ozone - protects life from UV radiation and life was able to expand to new environments
methanotrophs
microbes that eat methane using O2
(as opposed to methanogens that produce methane)
identifying methanotrophs in rock record
-extreme levels of 13C depletion in kerogens
- biomarkers in bacterial membranes
biomarkers
compounds found within bacterial membranes that can be altered and preserved in kerogen
chemical evidence for methotrophs
extremely light carbon values (enriched in C12) of -40 0/00 to -60 0/00 around 2.8-2.6 Ga
this require an extremely rich C12 environment which could be a result of methanogenic C12 production which were used by methanotrophic bacteria
