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Physiology and Diversity of Prokaryotes WS 2010/2011 (www.icbm.de/pmbio/)
PHOTOTROPHS
Martin Könneke
Lithotrophic Processes
Elektronendonor Oxidized product Process/ organism
H2
H+ (H2O)
Knallgas reaction/ Ralstonia
NH4
+
NO3
-
Nitrification (2 types)
NH4
+
NO2
-
Ammonia oxidizer (Nitroso-)
NO3
-
Nitrite oxidizer (Nitro-)
NO2
-
CH4
CO2
Methane oxidizer (Methylo-)
H2S, S
SO42-
Sulfur oxidizer/Thiobacillus,
Beggiatoa
Fe2+
Fe3+
Iron oxidation/Thiobacillus
H 2O
O2
Photosynthesis
1!
Lithotrophic processes are essential for the
reoxidation of reduced electron acceptors!
All chemolithotrophes are prokaryotes!
Almost all known lithotrophes are autotroph!
Energieform
Elektronendonor
Kohlenstoffquelle
Chemo-
Organo-
heterotroph
Photo-
Litho-
autotroph
2!
CO2 fixation pathways
At present, 6 different pathways are known,
just a single one within the Eukarya
Differ with regard to energy requirement, end
products and oxygene sensitivity
Calvin Cycle
Reductive (reverse) citric acid cycle
Reductive acetyl-CoA pathway
3-Hydroxypropionate cycle ( 3 variations)
3!
CO2 fixation: Calvin Cycle
Most widespead carbon fixation pathway
(RubisCO most abundant enzyme on Earth)
Occurs in chloroplast, cyanobacteria, and most
chemolithoautotrophic bacteria
Some bacteria contain speciallized compartements,
carboxysome, with high RubisCO concentration
Reduces CO2 even at high oxygen concentrations
Can also funtion as oxygenase
CO2 fixation via the Calvin Cycle
(Calvin-Bassham-Benson-cylcle)
Key enzyme: RubisCO
Ribulosebisphosphat-Carboxylase/Oxygenase
Used by all plants, cyanobacteria, and most of the aerobic
chemolithoautotrophic bacteria
Reduction of CO2 to the oxidation state of sugar:
CO2 + 3 ATP + 4[H] ! <CH2O> + H2O + 3 ADP + 3 Pi
- IV
0
4!
CO2 Fixierung:
Calvin Cycle
RubisCO
CO2 Fixierung: Calvin Cycle
15 C
3C
Phosphoribulokinase
18 C
3C
15 C
RubisCO
5!
CO2 fixation: Calvin Cycle
Key enzyme: RubisCO
Ribulosebisphosphat-Carboxylase/Oxygenase
Requirements for the synthesis of
3-phosphate glycerine aldehyde
3 CO2 + 9 ATP + 6 NADPH
carbon energy reducing power
Energy expensive pathway!
Reductive (reverse) citric acid cycle
Represents the reversion of the citric acid cycle
Replacement of 3 enzymes:
1) ATP-citrate lyase instead of the citrate synthase
2) !-ketoglutarate-synthase instead of "ketoglutaratedehydrogenase
3) Fumarate synthase instead of succinate dehydrogenase
Final product of the cycle is acetyl-CoA, that is further
carboxylized to pyruvate. A third step is the ATP dependent
conversion to triose-phosphate .
6!
Reductive citric acid pathway
Reductive citric acid pathway
7!
Reductive (reverse) citric acid cycle
Present in:
Phototrophic green sulfur bacteria (e.g. Chlorobium limicola)
Sulfate reducers (Desulfobacter hydrogenophilus)
Knallgas bacteria (Hydrogenobacter thermophilus)
Thermophilic, sulfur-reducing archaea (Thermoproteus
neutrophilus)
The acetyl-CoA pathway
-! In contrast to other carbon fixation pathways, not a cycle
-! two linear reaction series resulting in A) a methyl- and
B) a carbonyl group
-! key enzyme: CO-DH (Carbon monooxide dehydrogenase)
CO2 + H2 ! CO + H2O
-! The CO2 reduction must be considered as bifunctional
pathway: A) energy metabolism B) C-fixation for biosynthesis
8!
Reductive acetyl-CoA pathway
9!
3-Hydroxypropionate cycle
Reduction of bicarbonate to gyoxylate
Bicarbonate fixing enzymes are: acetyl-CoA
carboxylase and propionyl-CoA carboxylase
3-hydroxypropionyl-CoA as characteristic
intermediate
Recycling of the primary carbonate acceptor
acetyl-CoA
3-Hydroxypropionate cycle
10!
3-Hydroxypropionate cycle
3-Hydroxypropionate bicycle in Chloroflexus spec.
Zarzycki et al 2009
11!
3-Hydroxypropionate cycle
At present only found in the green nonsulfur
phototrophic members of the genus Chloroflexus
and in thermophilic Crenarchaeota
(Metallosphaera)
Suggested to be oldest pathway of autotrophy in
anoxygenic phototrophes
The
hydroxypropionate/
hydroxybutyrate cycle
in Crenarchaeota
Acetyl-CoA
Acetoacetyl-CoA !-ketothiolase
(Nmar_0841 or Nmar_1631)
Acetoacetyl-CoA
3-Hydroxybutyryl-CoA dehydrogenase
(Nmar_1028)
Acetyl-CoA
3-Hydroxybutyryl-CoA
HCO3-
Crotonyl-CoA hydratase
Acetyl-CoA carboxylase
(Nmar_1308)
(Nmar_0272, 0273, 0274)
Crotonyl-CoA
4-Hydroxybutyryl-CoA dehydratase
Malonyl-CoA
(Nmar_0207)
Malonyl-CoA reductase
Malonate semialdehyde reductase
4-Hydroxybutyryl-CoA
4-Hydroxybutyryl-CoA synthetase
(unknown)
(Nmar_0206)
3-Hydroxypropionate
3-Hydroxypropionyl-CoA synthetase
3-Hydroxypropionyl-CoA dehydratase
Acryloyl-CoA reductase (unknown)
Propionyl-CoA
Propionyl-CoA carboxylase
HCO3-
(Nmar_0272, 0273, 0274)
Methylmalonyl-CoA
4-Hydroxybutyrate
Succinate semialdehyde reductase
(Nmar_1110 or Nmar_0161)
Succinate-semialdehyde
Succinyl-CoA reductase
(Nmar_1608)
Succinyl-CoA
Methylmalonyl-CoA epimerase
Methylmalonyl-CoA mutase
(Nmar_0953, 0954, 0958)
12!
Berg et al. 2010
13!
14!
Photosynthetic organisms
Distinction between light and dark reaction
Light reaction conserve energy of light into
chemical energy (ATP)
Dark reaction involves the consumption of ATP for
fixation of CO2
Depending on electron donor:
Oxygen-producing: oxygenic
Non oxygen-producing: anoxigenic
Oxygenic photosynthesis
2e2H+
Water serves as electron donor
15!
Anoxygenic photosynthesis
Hydrogen sulfide (or sulfur) serves as electron donor
16!
17!
Structure of a chloroplast
Arrangement of light-harvesting
Chlorophylls
versus reaction center
18!
Phylogenetic affiliation of phototrophic bacteria
Oxigenic photosynthetic bacteria
Cyanobacteria
- Only bacteria which gain energy by oxigenic
photosynthesis (formation of O2)
- Large and heterogeneous group of bacteria
-! Major primary producer in many habitats (aquatic and
terrestrial habitats, symbiotic with Eukaryotes)
-! Ancestor of chloroplasts (Endosymbiosis theory)
-! Many can fix N2 (Heterocyst or temporal seperation)
-! Occur as unicellular and filamentous forms
19!
Absorption spectrum of cyanobacterium
20!
21!
22!
Phototrophic purple bacteria
- gain energy by anoxic photosynthesis (no formation of O2)
- contain bacteriochlorophyll and a variety of carotonoids
-! electron carriers are arranged in specific
intracytoplasmatic photosynthetic membranes (increase
of pigment density)
-! electron carriers are in the order of more electronegative
to higher electropositive reduction potential
Intracytoplasmic membranes
in anoxygenic phototrophs
23!
Phototrophic purple sulfur bacteria
Purple sulfur bacteria
e.g. Chromatium okenii
Gamma proteobacteria
Habitat: stratified lakes
Electron donor: reduced sulfur compounds
H2S, S0, S2O32Sulfur can be stores in globules inside the cell
Mixotrophic:
CO2 fixation (Calvin Cyclus), organic acids
Phototrophic purple sulfur bacteria
Purple sulfur bacteria
Ectothiorhodospira sp., Halorhodospira sp.
Gamma proteobacteria
Habitats: sola lakes, marine environments
halophilic = salt-loving
Produce sulfur outside the cell
Electron donor: reduced sulfur compounds
H2S, S0, S2O32Mixotrophic:
CO2 fixation (Calvin Cyclus), organic compounds
24!
Phototrophic purple nonsulfur bacteria
e.g. Rhodospirillum rubrum
Alpha or beta proteobacteria
Electron donor: hydrogen, sulfur, organic
substrates (no storage of sulfur)
Some can grow in the dark by fermentation,
anaerobic respiration, or aerobic respiration
Can also fix N2
Mixotrophic:
CO2 fixation (Calvin Cyclus), organic compounds
25!
Vesicular photosymthetic membranes
Rhodobacter
capsulatus
Anoxygenic photosynthesis
in purple bacteria
Only 1 light reaction!
26!
Arrangement of protein complexes in
phototrophic purple bacteria
Green sulfur bacteria
z.B. Chlorobium limicola
Phylum green sulfur bacteria
All isolates are obligate anaerobic and phototrophic
contain chlorosoms (location of photosynthesis)
electron donors: reduced sulfur compounds
H2S, S0, S2O32produced sulfur resides outside the cells
Mixotrophic:
CO2 fixation (reverse citric acid cycle)
organic compounds (photoheterotrophy)
27!
Chlorosomes in green sulfur bacteria
Chlorophyl-rich bodies, connected to cytoplasma membrane
Model of chlorosome structure (green
sulfur and green nonsulfur bacteria)
28!
Green Sulfur bacteria Consortia
"Chlorochromatium aggregatum"
Symbiosis between
Phototrophic green sulfur bacterium (epibiont)
and a chemotrophic beta proteobacterium
(by J. Overmann, mikrobiologischer-garten.de)
Green nonsulfur bacteria (“Chloroflexi“)
e.g. Chloroflexus aurantiacus
All isolated members are thermophilic
Formation of thick microbial mats in hot habitats.
Electron donor: H2 and organic compounds
CO2 fixation via 3-hydroxypropionate bicycle
Heterotrophic with organic acids
In the dark, chemoorganotrophic by aerobic respiration
29!
Green nonsulfur bacteria
(“Chloroflexi“)
Chloroflexus aurantiacus
Heliobacteria
z.B. Heliobacillus chlorum
contain bacteriochlorophyl g!
Strict anaerobic, N2-fixation!
Anoxygenic phototrophic Gram-positive bacteria!
Spore-forming
Electron donor: H2 and pyruvate (fermentation)
Mixotrophic:
CO2 fixation (reverse citric acid cycle)
organic compounds
30!
Bundles of cells of Heliophilum fasciatum
Spore formation
Heliobacterium gestii
31!
Physiological properties of phototrophic Bacteria
Cyanobacteria
Purplebacteria
Green
Sulfur bacteria
Green nonSulfur bacteria
Heliobacter
PS-type
PS I and II
PS II
PS I
PS II
PS I
Pigments
Chl a (b)
BChl a, b
BChl a, c, (d, e)
BChl a, c
BCHl g
Autotrophy
+
(+)
+
+/-
-!(?)
Physiology
PhotoautoLithoauto-
PhotoautoLithoautoOrganohetero-
PhotoautoLithoauto-
PhotoautoLithoautoOrganohetero-
PhotoautoOrganohetero-
CO2 fixation
Calvin-cycle
Calvin-cycle
Reductive TCA
3OH-Propionate
None ?
Electron donor
H 2O
H2S/ organic
H 2S
H2/ organic
Organic
Adapted from Fuchs and Schlegel
‘Allgemeine Mikrobiologie’
32!
Comparison of electron flow
33!