Metabolic Diversity: Phototrophy, Autotrophy, Chemolithotrophy, and Nitrogen Fixation

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


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


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)


Figure 20.1

Classification of Phototrophic Organisms


Figure 20.2

Patterns of Photosynthesis


Figure 20.2

Patterns of Photosynthesis



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


Figure 20.3a

Structure and Spectra of Chloro- and Bacteriochlorophyll


Figure 20.3b

Structure and Spectra of Chloro- and Bacteriochlorophyll

Absorption Spectrum


Figure 20.4

Structure of All Known Bacteriochlorophylls


Figure 20.4



Figure 20.4



Figure 20.5a

Photomicrograph of Algal Cell Showing Chloroplasts


Figure 20.5b

Chloroplast Structure



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


Figure 20.6

Arrangement of Light-Harvesting Chlorophylls


Figure 20.7

The Chlorosome of Green Sulfur and Nonsulfur Bacteria

Electron Micrograph of Cell of Green Sulfur Bacterium


Figure 20.7

The Chlorosome of Green Sulfur and Nonsulfur Bacteria

Model of Chromosome Structure



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


Figure 20.8

Structure of -carotene, a Typical Carotenoid


Figure 20.9

Structures of Some Common Carotenoids


Figure 20.9

Structures of Some Common Carotenoids



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


Figure 20.10

Phycobiliproteins and Phycobilisomes


Figure 20.11

Absorption Spectrum with an Accessory Pigment


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


Figure 20.12

Membranes in Anoxygenic Phototrophs

Chromatophores Lamellar Membranes in the Purple BacteriumEctothiorhodospira


Figure 20.13

Structure of Reaction Center in Purple Bacteria

Arrangement of Pigment Moleculesin Reaction Center


Figure 20.13

Structure of Reaction Center in Purple Bacteria

Molecular Model of the Protein Structure of the Reaction Center


Figure 20.14

Example of Electron Flow in Anoxygenic Photosynthesis


Figure 20.15

Arrangement of Protein Complexes in Reaction Center


Figure 20.16

Map of Photosynthetic Gene Cluster in Purple Phototroph


Figure 20.17

Phototrophic Purple and Green Sulfur Bacteria

Purple Bacterium, Chromatium okenii Green Bacterium, Chlorobium limicola


Figure 20.18

Electron Flow in Purple, Green, Sulfur and Heliobacteria


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


Figure 20.19

The “Z scheme” in Oxygenic Photosynthesis


II. Autotrophy

20.6 The Calvin Cycle

20.7 Other Autotrophic Pathways in Phototrophs


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


Figure 20.21a

Key Reactions of the Calvin Cycle


Figure 20.21b



Figure 20.21c



Figure 20.22

The Calvin Cycle


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


Figure 20.24a

Autotrophic Pathways in Phototrophic Green Bacteria


Figure 20.24b

Autotrophic Pathways in Phototrophic Green Bacteria


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


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


Energy Yields from Oxidation of Inorganic Electron Donors


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


Figure 20.25

Two Hydrogenases of Aerobic H2 Bacteria


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


Figure 20.26

Sulfur Bacteria


Figure 20.27a

Oxidation of Reduced Sulfur Compounds

Steps in the Oxidation of Different Compounds


Figure 20.27b

Oxidation of Reduced Sulfur Compounds


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


Figure 20.28

Iron-Oxidizing Bacteria

Acid Mine Drainage


Figure 20.28

Iron-Oxidizing Bacteria

Cultures of A. Ferrooxidans Shown in Dillution Series


Figure 20.29

Iron Bacteria Growing at Neutral pH: Sphaerotilus


Figure 20.30

Electron Flow During Fe2+ Oxidation


Fe2+ Oxidation in Anoxic Tube CulturesFigure 20.31

Ferrous Iron Oxidation by Anoxygenic Phototrophs


Figure 20.31

Ferrous Iron Oxidation by Anoxygenic Phototrophs

Phase-contrast Photomicrograph Of an Iron-Oxidizing Purple Bacterium


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


Figure 20.32

Oxidation of Ammonia by Ammonia-Oxidizing Bacteria


Figure 20.33

Oxidation of Nitrite to Nitrate by Nitrifying Bacteria


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


Figure 20.34a-b

Anammox

Phase-contrast Photomicrograph of Brocadia Anammoxidans cells

Transmission Electronic Micrograph of a Cell


Figure 20.34c

Reactions in the Anammoxosome


IV. Nitrogen Fixation

20.14 Nitrogenase and Nitrogen Fixation

20.15 Genetics and Regulation of Nitrogen Fixation


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


Figure 20.35

FeMo-co, the Iron-Molybdenum Cofactor from Nitrogenase


Figure 20.36

Nitrogenase Function


Figure 20.37

Induction of Slime Formation by O2 in Nitrogen-Fixing Cells


Figure 20.38

Reaction of Nitrogen Fixation in S. thermoautotrophicus


Figure 20.39

The Acetylene Reduction Assay for Nitrogenase Activity


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


Figure 20.40

The nif regulon in K. pneumoniae

Documents

Metabolic Diversity: Phototrophy, Autotrophy, Chemolithotrophy, and Nitrogen Fixation