which microbes use photosynthesis
Photosynthetic Prokaryotes
-Cyanobacteria (oxygenic phototrophs)
-Purple bacteria (anoxygenic)
-Green sulfur bacteria (anoxygenic)
-Green non-sulfur bacteria (anoxygenic)
-Heliobacteria
Photosynthetic Eukaryotes
-Algae
-Plants
what is the energy source, e- source, carbon source for phototrophy
energy source = light = photo
e- source = inorganic = litho
carbon source = inorganic/C1 = auto
or = organic = hetero
autotrophic
- fix CO2 to organic carbon
- primary producers
-> algae from cyanobacteria, purple bacteria, green sulfur bacteria, photosynthetic eukaryotes
heterotrophic
- require an external organic carbon source
-> green non-sulfur bacteria, heliobacteria, some purple bacteria
what are the 2 types of photosynthesis - how did they arise (oxygenation)
- anoxygenic phototrophs harvested energy from light in shallow ancient ocean
-> does not produce oxygen - oxygenic phototrophs (cyanobacteria) evolved from them
-> produces oxygen
-> the great oxidation event - oxygenation resulted in mass extinction but resulted in enhanced primary production and enabled diversification and new metabolisms that led to the evolution of multicellularity
cyanobacteria
- oxygenic photosynthesis
- chlorophyll A and B
- contains chloroplast
explain oxygenic photosynthesis
- photons excite chlorophyll which excite e- in the reaction centers of PSl and PSll = decreasing their reduction potentials (makes them good e- donors)
- cyclic photophosphorylation involved only PSl (P700) and is used for producing ATP
- non-cyclic photophosphorylation is used to generate reducing power (NADPH)
- e- are donated by H2O to PSll (P680)
- NADPH is used for CO2 fixation (dark reactions when associated with photosynthesis)
non-cyclic
-H2O gives e- -> P680 gets excited, protons -> Cyt b6 -> P700 ->PMF -> Fd -> e- donated to NADP+ -> NADPH
cyclic
-Fd gives e- back to cyt b -> P700 -> produce ATP
what is anoxygenic photosynthesis for purple non-sulfur and green sulfur bacteria
purple non-sulfur bacteria
- e- donors = H2, organics, H2S
- reduction potential of NAD+ (E=0.32V) is too low to spontaneously receive e- from cyt b/c1(E=o.25V)
- reducing power must be generated using PMF to drive excitation of e- to reduce NAD+
-> reverse electron flow to produce NADH
green sulfur bacteria
- e- donors = H2S, So, thiosulfate
- can divert e- directly to NAD+ (E=-0.32V) from Fd (E= -0.42) to generate reducing power
explain reverse e- transport
- many chemolithotrophs and anoxygenic phototrophs do not have e- at a sufficiently low reduction potential to generate reducing power
- use reverse e- flow to generate reducing power
- requires energy input to transfer to NADP+ or FAD = to move e- up the tower
- proton gradient provides the energy
what is the energy source, e- source, and carbon source for chemolithotrophy
energy source = chemical = chemo
e- source = inorganic = litho
carbon source = inorganic = auto or organic = hetero
- occurs under aerobic and anerobic conditions
- metabolism is linked to an electron transport chain
- many chemolithotrophs are also autotrophs = need to produce substantial reducing power
-> reverse electron transport chain is required
hydrogen oxidation - chemolithotrophy
- H2 = excellent e- donor
- TEA = oxygen, nitrate, Fe3+, sulfate/sulfur, CO2
- key enzyme = hydrogenase
- can transfer e- directly to NAD(P)+
- cytoplasmic or membrane associated
methanogenesis - chemolithotrophy
- hydrogenotrophic methanogenesis involves H2 oxidation coupled to CO2 reduction
- methane = product
- strictly anaerobic process = methanogens are sensitive to O2
- all methanogens = archaea (phylum euryarchaeota)
- key enzyme = methyl coenzyme-M reductase (mcr) -> catalyzes the last 3 steps
- specialized co factors are required for metabolism
-> MFR, tetra hydromethanopterin = 1C carrier
-> coenzyme F420 = e- carrier
-> coenzyme F430 = e- carrier with CoM - delta G = -130
what is the significance of methanogenesis
- mineralization of organic matter in the subsurface
- mammalian gut - especially ruminants
- biogenic methane (natural gas)
-> from coal and oil deposits - anerobic digestion -> biogas
-> from compost, wastewater sludge, agricultural waste
nitrification - chemolithotrophy
- microbial oxidation of NH4+ to NO3- with oxygen as TEA
-> occurs within 2 different functional types - ammonia oxidizing bacteria and archaea (AOB)
-> key enzyme = ammonia monooxygenase (delta G = -275)
-nitrite oxidizing bacteria (NOB)
-> key enzyme = nitrite oxidoreductase (delta G= -74)
difference between AOM and NOB
AOM
- ammonia monooxygenase (AMO)
- hydroxylamine oxidoreductase (HAO)
NOB
- nitrite (oxido)reductase
- reverse electron transport is required to make reducing power for CO2 fixation (NADH)
anammox (anaerobic ammonia oxidation) - chemolithotrophy
- oxidation of ammonia coupled to nitrite reduction to N2
- anammox bacteria are restricted to the order brocadiales in the phylum planctomycetes
- 7 known species => none isolated in pure culture
- hydrazine (rocket fuel) is an intermediate of metabolism
-> metabolism is performed in a specialized organelle -> the anammoxosome to protect cells from reactive intermediates - beneficial process for wastewater treatment as oxygen is not required
-> significantly reduces energy needs for wastewater treatment (50-90%)
how does the mechanism of anammox work
- protons accumulate inside the anammoxosome, generating a PMF
- ATP synthesis is located in the anammoxosome membrane
- hydrazine is very electronegative which allows it to donate electrons to ferredoxin (E=-0.42)
- key enzyme = hydrazine synthase
what is syntrophy
- symbiotic metabolism process in which 2 different organisms cooperate to degrade a substance and conserve energy
- can’t degrade substance along (endergonic)
- syntrophs are mostly fermenters yielding H2, CO2 and acetate as end products
- > syntrophobacter, syntrophomonas
- combines chemoorganotrophic and chemolithotrophic reactions
how is H2 used as a fermentation product
- synthesis of H2 and acetate as fermentation products from pyruvate
- when acetate is produced, ATP can also be synthesized
- often catalyzed by enteric bacteria (living in your gut) / mixed acid fermentation
How does syntrophy makes unfavorable reactions feasible
- many fermentations are not thermodynamically feasible at standard conditions
-> butyrate +2 H2O -> 2 acetate + H+ + 2H2
solution
- remove the products -> bring them to low concentration (H2 in the environment often <1x10^-4 atm)
- couple this unfavorable reaction to a favorable one that consumes H2
-> 4H2 + CO2 -> CH4 + 2H2O (delta G =-130)
what is interspecies H2 transfer
- H2 production by one partner (the syntroph) is linked to the H2 consumption of the other
- removal of the product H2 pulls ethanol fermentation to the right, overall reaction is exergonic
- free energy released is shared by two organisms
- H2 transferred from the syntroph to the methanogen = interspecies H2 transfer
anaerobic foodwebs
- drives carbon cycling in both natural and engineered anoxic environments
- consortia of different microbes
-> hydrolysis -> fermentation -> terminal respiration - Terminal respiration by:
->Denitrifiers
->Sulfate reducers
->Metal reducers
->Methanogens
->Acetogens
assimilatory vs dissimilatory reduction
assimilation (anabolism)
-> the reduction of inorganic sources of elements into organic forms for biosynthesis
(CO2, N2, NO3-, SO42-)
- only enough reduction to satisfy the needs of biosynthesis
- requires an input of energy
dissimilation (catabolism)
- reduction of inorganic forms for energy production
- electron acceptor gets reduced and excreted
- large amount of electron acceptor is used
- associated with energy generation
N-autotrophy = Diazotrophy
- fixing N2 to NH3
- only by some bacteria and methanogenic archaea
- nitrogenase = key enzyme
-> oxygen sensitive, Fe-Mo-cofactor
