Page 1
Copyright © 2009 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Brock Biology of Microorganisms
Twelfth Edition
Madigan / Martinko Dunlap / Clark
Metabolic Diversity: Phototrophy, Autotrophy, Chemolithotrophy, and Nitrogen Fixation
Chap
ter 2
0
Lectures by Buchan & LeCleir
Page 2
Copyright © 2009 Pearson Education Inc., publishing as Pearson Benjamin Cummings
I. The Phototrophic Way of Life
20.1 Photosynthesis
20.2 Chlorophylls and Bacteriochlorophylls
20.3 Carotenoids and Phycobilins
20.4 Anoxygenic Photosynthesis
20.5 Oxygenic Photosynthesis
Page 3
Copyright © 2009 Pearson Education Inc., publishing as Pearson Benjamin Cummings
20.1 Photosynthesis
Photosynthesis is the most important biological process on
Earth Phototrophs are organisms that carry out photosynthesis
Most phototrophs are also autotrophs
Photosynthesis requires light-sensitive pigments called
chlorophyll
Photoautotrophy requires ATP production and CO2 reduction
Oxidation of H2O produces O2 (oxygenic photosynthesis)
Oxygen not produced (anoxygenic photosynsthesis)
Page 4
Copyright © 2009 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Figure 20.1
Classification of Phototrophic Organisms
Page 5
Copyright © 2009 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Figure 20.2
Patterns of Photosynthesis
Page 6
Copyright © 2009 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Figure 20.2
Patterns of Photosynthesis
Page 7
Copyright © 2009 Pearson Education Inc., publishing as Pearson Benjamin Cummings
20.2 Chlorophylls and Bacteriochlorophylls
Organisms must produce some form of chlorophyll (or
bacteriochlorophyll) to be photosynthetic
Chlorophyll is a porphyrin
Number of different types of chlorophyll exist Different chlorophylls have different absorption spectra
Chlorophyll pigments are located within special
membranes In eukaryotes, called thylakoids
In prokaryotes, pigments are integrated into cytoplasmic
membrane
Page 8
Copyright © 2009 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Figure 20.3a
Structure and Spectra of Chloro- and Bacteriochlorophyll
Page 9
Copyright © 2009 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Figure 20.3b
Structure and Spectra of Chloro- and Bacteriochlorophyll
Absorption Spectrum
Page 10
Copyright © 2009 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Figure 20.4
Structure of All Known Bacteriochlorophylls
Page 11
Copyright © 2009 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Figure 20.4
Structure of All Known Bacteriochlorophylls
Page 12
Copyright © 2009 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Figure 20.4
Structure of All Known Bacteriochlorophylls
Page 13
Copyright © 2009 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Figure 20.5a
Photomicrograph of Algal Cell Showing Chloroplasts
Page 14
Copyright © 2009 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Figure 20.5b
Chloroplast Structure
Page 15
Copyright © 2009 Pearson Education Inc., publishing as Pearson Benjamin Cummings
20.2 Chlorophylls and Bacteriochlorophylls
Reaction centers participate directly in the conversion
of light energy to ATP
Antenna pigments funnel light energy to reaction
centers
Chlorosomes function as massive antenna complexes
Found in green sulfur bacteria
Page 16
Copyright © 2009 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Figure 20.6
Arrangement of Light-Harvesting Chlorophylls
Page 17
Copyright © 2009 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Figure 20.7
The Chlorosome of Green Sulfur and Nonsulfur Bacteria
Electron Micrograph of Cell of Green Sulfur Bacterium
Page 18
Copyright © 2009 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Figure 20.7
The Chlorosome of Green Sulfur and Nonsulfur Bacteria
Model of Chromosome Structure
Page 19
Copyright © 2009 Pearson Education Inc., publishing as Pearson Benjamin Cummings
20.3 Carotenoids and Phycobilins
Phototrophic organisms have accessory pigments in
addition to chlorophyll, including carotenoids and
phycobiliproteins
Carotenoids
Always found in phototrophic organisms
Typically yellow, red, brown, or green
Energy absorbed by carotenoids can be transferred to a
reaction center
Prevent photo-oxidative damage to cells
Page 20
Copyright © 2009 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Figure 20.8
Structure of -carotene, a Typical Carotenoid
Page 21
Copyright © 2009 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Figure 20.9
Structures of Some Common Carotenoids
Page 22
Copyright © 2009 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Figure 20.9
Structures of Some Common Carotenoids
Page 23
Copyright © 2009 Pearson Education Inc., publishing as Pearson Benjamin Cummings
20.3 Carotenoids and Phycobilins
Phycobiliproteins are main antenna pigments of
cyanobacteria and red algae
Form into aggregates within the cell called
phycobilisomes
Allow cell to capture more light energy than
chlorophyll alone
Page 24
Copyright © 2009 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Figure 20.10
Phycobiliproteins and Phycobilisomes
Page 25
Copyright © 2009 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Figure 20.11
Absorption Spectrum with an Accessory Pigment
Page 26
Copyright © 2009 Pearson Education Inc., publishing as Pearson Benjamin Cummings
20.4 Anoxygenic Photosynthesis
Anoxygenic photosynthesis is found in at least four
phyla of Bacteria
Electron transport reactions occur in the reaction
center of anoxygenic phototrophs
Reducing power for CO2 fixation comes from reductants
present in the environment (i.e., H2S, Fe2+, or NO2-)
Requires reverse electron transport for NADH production in
purple phototrophs
Page 27
Copyright © 2009 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Figure 20.12
Membranes in Anoxygenic Phototrophs
Chromatophores Lamellar Membranes in the Purple BacteriumEctothiorhodospira
Page 28
Copyright © 2009 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Figure 20.13
Structure of Reaction Center in Purple Bacteria
Arrangement of Pigment Moleculesin Reaction Center
Page 29
Copyright © 2009 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Figure 20.13
Structure of Reaction Center in Purple Bacteria
Molecular Model of the Protein Structure of the Reaction Center
Page 30
Copyright © 2009 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Figure 20.14
Example of Electron Flow in Anoxygenic Photosynthesis
Page 31
Copyright © 2009 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Figure 20.15
Arrangement of Protein Complexes in Reaction Center
Page 32
Copyright © 2009 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Figure 20.16
Map of Photosynthetic Gene Cluster in Purple Phototroph
Page 33
Copyright © 2009 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Figure 20.17
Phototrophic Purple and Green Sulfur Bacteria
Purple Bacterium, Chromatium okenii Green Bacterium, Chlorobium limicola
Page 34
Copyright © 2009 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Figure 20.18
Electron Flow in Purple, Green, Sulfur and Heliobacteria
Page 35
Copyright © 2009 Pearson Education Inc., publishing as Pearson Benjamin Cummings
20.5 Oxygenic Photosynthesis
Oxygenic phototrophs use light to generate ATP and
NADPH
The two light reactions are called photosystem I and
photosystem II
“Z scheme” of photosynthesis
Photosystem II transfers energy to photosystem I
ATP can also be produced by cyclic photophosphorylation
Page 36
Copyright © 2009 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Figure 20.19
The “Z scheme” in Oxygenic Photosynthesis
Page 37
Copyright © 2009 Pearson Education Inc., publishing as Pearson Benjamin Cummings
II. Autotrophy
20.6 The Calvin Cycle
20.7 Other Autotrophic Pathways in Phototrophs
Page 38
Copyright © 2009 Pearson Education Inc., publishing as Pearson Benjamin Cummings
20.6 The Calvin Cycle
The Calvin Cycle Named for its discoverer Melvin Calvin
Fixes CO2 into cellular material for autotrophic growth
Requires NADPH, ATP, ribulose bisphophate
carboxylase (RubisCO), and phosphoribulokinase
6 molecules of CO2 are required to make 1 molecule
of glucose
Page 39
Copyright © 2009 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Figure 20.21a
Key Reactions of the Calvin Cycle
Page 40
Copyright © 2009 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Figure 20.21b
Key Reactions of the Calvin Cycle
Page 41
Copyright © 2009 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Figure 20.21c
Key Reactions of the Calvin Cycle
Page 42
Copyright © 2009 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Figure 20.22
The Calvin Cycle
Page 43
Copyright © 2009 Pearson Education Inc., publishing as Pearson Benjamin Cummings
20.7 Other Autotrophic Pathways in Phototrophs
Green sulfur bacteria use the reverse citric acid cycle
to fix CO2
Green nonsulfur bacteria use the hydroxyproprionate
pathway to fix CO2
Page 44
Copyright © 2009 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Figure 20.24a
Autotrophic Pathways in Phototrophic Green Bacteria
Page 45
Copyright © 2009 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Figure 20.24b
Autotrophic Pathways in Phototrophic Green Bacteria
Page 46
Copyright © 2009 Pearson Education Inc., publishing as Pearson Benjamin Cummings
III. Chemolithotrophy
20.8 The Energetics of Chemolithotrophy
20.9 Hydrogen Oxidation
20.10 Oxidation of Reduced Sulfur Compounds
20.11 Iron Oxidation
20.12 Nitrification
20.13 Anammox
Page 47
Copyright © 2009 Pearson Education Inc., publishing as Pearson Benjamin Cummings
20.8 The Energetics of Chemolithotrophy
Chemolithotrophs are organisms that obtain energy
from the oxidation of inorganic compounds
Mixotrophs are chemolithotrophs that require organic
carbon as a carbon source
Many sources of reduced molecules exist in the
environment
The oxidation of different reduced compounds yields
varying amounts of energy
Page 48
Copyright © 2009 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Energy Yields from Oxidation of Inorganic Electron Donors
Page 49
Copyright © 2009 Pearson Education Inc., publishing as Pearson Benjamin Cummings
20.9 Hydrogen Oxidation
Anaerobic H2 oxidizing Bacteria and Archaea are
known
Catalyzed by hydrogenase
In the presence of organic compounds such as
glucose, synthesis of Calvin cycle and hydrogenase
enzymes is repressed
Page 50
Copyright © 2009 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Figure 20.25
Two Hydrogenases of Aerobic H2 Bacteria
Page 51
Copyright © 2009 Pearson Education Inc., publishing as Pearson Benjamin Cummings
20.10 Oxidation of Reduced Sulfur Compounds
Many reduced sulfur compounds are used as electron donors
Discovered by Sergei Winogradsky
H2S, S0, S2O3- are commonly used
One product of sulfur oxidation is H+, which results in a
lowering of the pH of its surroundings
Sox system oxidizes reduced sulfur compounds directly to
sulfate
Usually aerobic, but some organisms can use nitrate as an
electron acceptor
Page 52
Copyright © 2009 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Figure 20.26
Sulfur Bacteria
Page 53
Copyright © 2009 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Figure 20.27a
Oxidation of Reduced Sulfur Compounds
Steps in the Oxidation of Different Compounds
Page 54
Copyright © 2009 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Figure 20.27b
Oxidation of Reduced Sulfur Compounds
Page 55
Copyright © 2009 Pearson Education Inc., publishing as Pearson Benjamin Cummings
20.11 Iron Oxidation
Ferrous iron (Fe2+) oxidized to ferric iron (Fe3+)
Ferric hydroxide precipitates in water
Many Fe oxidizers can grow at pH <1
Often associated with acidic pollution from coal mining
activities
Some anoxygenic phototrophs can oxidize Fe2+
anaerobically using Fe2+ as an electron donor for CO2
reduction
Page 56
Copyright © 2009 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Figure 20.28
Iron-Oxidizing Bacteria
Acid Mine Drainage
Page 57
Copyright © 2009 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Figure 20.28
Iron-Oxidizing Bacteria
Cultures of A. Ferrooxidans Shown in Dillution Series
Page 58
Copyright © 2009 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Figure 20.29
Iron Bacteria Growing at Neutral pH: Sphaerotilus
Page 59
Copyright © 2009 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Figure 20.30
Electron Flow During Fe2+ Oxidation
Page 60
Copyright © 2009 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Fe2+ Oxidation in Anoxic Tube CulturesFigure 20.31
Ferrous Iron Oxidation by Anoxygenic Phototrophs
Page 61
Copyright © 2009 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Figure 20.31
Ferrous Iron Oxidation by Anoxygenic Phototrophs
Phase-contrast Photomicrograph Of an Iron-Oxidizing Purple Bacterium
Page 62
Copyright © 2009 Pearson Education Inc., publishing as Pearson Benjamin Cummings
20.12 Nitrification
NH3 and NO2- are oxidized by nitrifying bacteria during the
process of nitrification
Two groups of bacteria work in concert to fully oxidize
ammonia to nitrate
Key enzymes are ammonia monooxygenase,
hydroxylamine oxidoreductase, and nitrite oxidoreductase
Only small energy yields from this reaction
Growth of nitrifying bacteria is very slow
Page 63
Copyright © 2009 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Figure 20.32
Oxidation of Ammonia by Ammonia-Oxidizing Bacteria
Page 64
Copyright © 2009 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Figure 20.33
Oxidation of Nitrite to Nitrate by Nitrifying Bacteria
Page 65
Copyright © 2009 Pearson Education Inc., publishing as Pearson Benjamin Cummings
20.13 Anammox
Anammox: anoxic ammonia oxidation
Performed by unusual group of obligate aerobes
Anammoxosome is compartment where anammox
reactions occur
Protects cell from reactions occuring during anammox
Hydrazine is an intermediate of anammox
Anammox is very beneficial in the treatment of sewage
and wastewater
Page 66
Copyright © 2009 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Figure 20.34a-b
Anammox
Phase-contrast Photomicrograph of Brocadia Anammoxidans cells
Transmission Electronic Micrograph of a Cell
Page 67
Copyright © 2009 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Figure 20.34c
Reactions in the Anammoxosome
Page 68
Copyright © 2009 Pearson Education Inc., publishing as Pearson Benjamin Cummings
IV. Nitrogen Fixation
20.14 Nitrogenase and Nitrogen Fixation
20.15 Genetics and Regulation of Nitrogen Fixation
Page 69
Copyright © 2009 Pearson Education Inc., publishing as Pearson Benjamin Cummings
20.14 Nitrogenase and Nitrogen Fixation
Only certain prokaryotes can fix nitrogen
Some nitrogen fixers are free living and others are
symbiotic
Reaction is catalyzed by nitrogenase
Sensitive to the presence of oxygen
A wide variety of nitrogenases use different metal
cofactors
Nitrogenase activity can be assayed using the acetylene
reduction assay
Page 70
Copyright © 2009 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Figure 20.35
FeMo-co, the Iron-Molybdenum Cofactor from Nitrogenase
Page 71
Copyright © 2009 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Figure 20.36
Nitrogenase Function
Page 72
Copyright © 2009 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Figure 20.37
Induction of Slime Formation by O2 in Nitrogen-Fixing Cells
Page 73
Copyright © 2009 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Figure 20.38
Reaction of Nitrogen Fixation in S. thermoautotrophicus
Page 74
Copyright © 2009 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Figure 20.39
The Acetylene Reduction Assay for Nitrogenase Activity
Page 75
Copyright © 2009 Pearson Education Inc., publishing as Pearson Benjamin Cummings
20.15 Genetics and Regulation of Nitrogen Fixation
Highly regulated process because it is such an energy-
demanding process
nif regulon coordinates regulation of genes essential to
nitrogen fixation
Oxygen and ammonia are the two main regulatory
effectors
Page 76
Copyright © 2009 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Figure 20.40
The nif regulon in K. pneumoniae