Download Metabolic Diversity: Phototrophy, Autotrophy, Chemolithotrophy

Brock Biology of
Microorganisms
Twelfth Edition
Madigan / Martinko
Chapter 20
Dunlap / Clark
Metabolic Diversity: Phototrophy, Autotrophy, Chemolithotrophy,
and Nitrogen Fixation
Lectures by Buchan & LeCleir
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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
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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)
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Classification of Phototrophic Organisms
Figure 20.1
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Patterns of Photosynthesis
Figure 20.2
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Patterns of Photosynthesis
Figure 20.2
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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
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Structure and Spectra of Chloro- and Bacteriochlorophyll
Figure 20.3a
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Structure and Spectra of Chloro- and Bacteriochlorophyll
Absorption Spectrum
Figure 20.3b
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Structure of All Known Bacteriochlorophylls
Figure 20.4
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Structure of All Known Bacteriochlorophylls
Figure 20.4
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Structure of All Known Bacteriochlorophylls
Figure 20.4
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Photomicrograph of Algal Cell Showing Chloroplasts
Figure 20.5a
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Chloroplast Structure
Figure 20.5b
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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
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Arrangement of Light-Harvesting Chlorophylls
Figure 20.6
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The Chlorosome of Green Sulfur and Nonsulfur Bacteria
Electron Micrograph of Cell of Green Sulfur Bacterium
Figure 20.7
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The Chlorosome of Green Sulfur and Nonsulfur Bacteria
Model of Chromosome Structure
Figure 20.7
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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
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Structure of -carotene, a Typical Carotenoid
Figure 20.8
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Structures of Some Common Carotenoids
Figure 20.9
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Structures of Some Common Carotenoids
Figure 20.9
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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
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Phycobiliproteins and Phycobilisomes
Figure 20.10
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Absorption Spectrum with an Accessory Pigment
Figure 20.11
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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
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Membranes in Anoxygenic Phototrophs
Chromatophores
Lamellar Membranes in the Purple Bacterium
Ectothiorhodospira
Figure 20.12
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Structure of Reaction Center in Purple Bacteria
Arrangement of Pigment Molecules
in Reaction Center
Figure 20.13
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Structure of Reaction Center in Purple Bacteria
Molecular Model of the Protein Structure
of the Reaction Center
Figure 20.13
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Example of Electron Flow in Anoxygenic Photosynthesis
Figure 20.14
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Arrangement of Protein Complexes in Reaction Center
Figure 20.15
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Map of Photosynthetic Gene Cluster in Purple Phototroph
Figure 20.16
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Phototrophic Purple and Green Sulfur Bacteria
Purple Bacterium, Chromatium okenii
Green Bacterium, Chlorobium limicola
Figure 20.17
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Electron Flow in Purple, Green, Sulfur and Heliobacteria
Figure 20.18
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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
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The “Z scheme” in Oxygenic Photosynthesis
Figure 20.19
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II. Autotrophy
 20.6 The Calvin Cycle
 20.7 Other Autotrophic Pathways in Phototrophs
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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
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Key Reactions of the Calvin Cycle
Figure 20.21a
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Key Reactions of the Calvin Cycle
Figure 20.21b
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Key Reactions of the Calvin Cycle
Figure 20.21c
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The Calvin Cycle
Figure 20.22
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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
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Autotrophic Pathways in Phototrophic Green Bacteria
Figure 20.24a
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Autotrophic Pathways in Phototrophic Green Bacteria
Figure 20.24b
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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
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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
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Energy Yields from Oxidation of Inorganic Electron Donors
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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
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Two Hydrogenases of Aerobic H2 Bacteria
Figure 20.25
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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
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Sulfur Bacteria
Figure 20.26
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Oxidation of Reduced Sulfur Compounds
Steps in the Oxidation of Different Compounds
Figure 20.27a
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Oxidation of Reduced Sulfur Compounds
Figure 20.27b
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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
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Iron-Oxidizing Bacteria
Acid Mine Drainage
Figure 20.28
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Iron-Oxidizing Bacteria
Cultures of A. Ferrooxidans Shown
in Dillution Series
Figure 20.28
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Iron Bacteria Growing at Neutral pH: Sphaerotilus
Figure 20.29
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Electron Flow During Fe2+ Oxidation
Figure 20.30
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Ferrous Iron Oxidation by Anoxygenic Phototrophs
Fe2+ Oxidation in Anoxic Tube Cultures
Figure 20.31
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Ferrous Iron Oxidation by Anoxygenic Phototrophs
Phase-contrast Photomicrograph
Of an Iron-Oxidizing Purple Bacterium
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Figure 20.31
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
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Oxidation of Ammonia by Ammonia-Oxidizing Bacteria
Figure 20.32
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Oxidation of Nitrite to Nitrate by Nitrifying Bacteria
Figure 20.33
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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
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Anammox
Phase-contrast Photomicrograph of
Brocadia Anammoxidans cells
Transmission Electronic Micrograph of a Cell
Figure 20.34a-b
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Reactions in the Anammoxosome
Figure 20.34c
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IV. Nitrogen Fixation
 20.14 Nitrogenase and Nitrogen Fixation
 20.15 Genetics and Regulation of Nitrogen Fixation
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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
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FeMo-co, the Iron-Molybdenum Cofactor from Nitrogenase
Figure 20.35
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Nitrogenase Function
Figure 20.36
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Induction of Slime Formation by O2 in Nitrogen-Fixing Cells
Figure 20.37
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Reaction of Nitrogen Fixation in S. thermoautotrophicus
Figure 20.38
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The Acetylene Reduction Assay for Nitrogenase Activity
Figure 20.39
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20.15 Genetics and Regulation of Nitrogen Fixation
 Highly regulated process because it is such an energydemanding process
 nif regulon coordinates regulation of genes essential to
nitrogen fixation
 Oxygen and ammonia are the two main regulatory
effectors
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The nif regulon in K. pneumoniae
Figure 20.40
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