Microbiology - Ch. 13 - Microbe Evolution And Systematics

Front 1

Origin of Earth

Back 1

Earth is ~4.5 billion years old.

Liquid water required for life; first appeared ~4.3 billion years ago.

Evidence for life ~4.1 billion years ago.

Fossilized remains of cells can be found in rocks ~3.86 billion years old.

Front 2

Origin of Cellular Life Pt. 1

Back 2

Life may have originated at hydrothermal systems on ocean floor.

Conditions would have been more stable.

Steady and abundant supply of energy (e.g., H2 and H2S) may have been available at these sites.

Front 3

Origin of Cellular Life Pt. 2

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Geochemistry can support abiotic production of molecules required for life (e.g., amino acids, lipids, sugars, and nucleotides).

Mineral structures may have produced compartments for conserving energy.

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Life May Have Begun in an RNA World Pt. 1

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RNA is part of essential cofactors and molecules (e.g., ATP, NADH, coenzyme A).

RNA can bind small molecules (e.g., ATP, other nucleotides, amino acids).

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Life May Have Begun in an RNA World Pt. 2

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RNA has catalytic activity; may have catalyzed its own synthesis.

Earliest viruses may have evolved from RNA genome cell-like structures.

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Origin of Cellular Life Pt. 3

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Proteins eventually replaced RNAs as catalysts.

DNA (more stable) became genome and template.

Earliest cells probably had DNA, RNA, protein, and membrane system for energy conservation.

Front 7

LUCA

Back 7

Last Universal Common Ancestor.

(LUCA) existed 3.8–3.7 billion years ago, then Bacteria and Archaea diverged.

Front 8

Metabolic Diversification: Consequences for Earth’s Biosphere Pt. 1

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Because early Earth was anoxic, energy-generating metabolism of primitive cells was exclusively anaerobic.

Obtained carbon from CO2 (autotrophy).

Evolved ability to use N2 (nitrogen fixation).

Obtained energy from H2; S may have been an early electron acceptor.

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Metabolic Diversification: Consequences for Earth’s Biosphere Pt. 2

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Early forms of chemolithotrophic metabolism would have supported production of large amounts of organic compounds.

Accumulated organic material provided conditions needed for evolution of chemoorganotrophic metabolisms.

Eventually Earth became highly oxic.

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Photosynthesis and the Oxidation of Earth Pt. 1

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Phototrophs use energy from sun to oxidize H2S, S, and H2O to synthesize complex organic molecules from CO2 or simple organics.

First phototrophs were anoxygenic.

Cyanobacteria (O2 producers; oxygenic phototrophs) evolved.

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Photosynthesis and the Oxidation of Earth Pt. 2

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Stromatolites (fossilized microbial formations) found in rocks 3.5 billion years old.

Phototrophic bacteria (cyanobacteria and Chloroflexus) from modern stromatolites.

Ancient stromatolites contain fossils similar to modern phototrophic bacteria.

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Photosynthesis and the Oxidation of Earth Pt. 3

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Between 2.5 and 3.3 billion years ago, cyanobacteria evolved a photosystem that could use H2O instead of H2S, generating O2.

Rise of O2 allowed evolution of life to exploit energy from O2 respiration.

Front 13

The Rise of Oxygen: Banded Iron Formations (Part 1)

Back 13

Most iron would have been reduced (Fe0 and Fe+2) and dissolved in anoxic oceans.

O2 produced reacted spontaneously with reduced iron forming iron oxides instead of accumulating.

By 2.4 billion years ago, O2 rose to one part per million (Great Oxidation Event).

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The Rise of Oxygen: Banded Iron Formations (Part 2)

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Iron oxides precipitated and formed banded iron formations: laminated sedimentary rocks.

Atmosphere gradually became oxic.

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The Rise of Oxygen: Banded Iron Formations (Part 3)

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New metabolisms (e.g., sulfide oxidation, nitrification, other aerobic chemolithotrophy) evolved.

Respiring O2 energetically advantageous because of high reduction potential, allowing aerobes to reproduce much faster than anaerobes.

Front 16

The Ozone Shield

Back 16

Formation of ozone (O3) shield that protects Earth’s surface from UV radiation.

Before, Earth’s surface was inhospitable.

Ozone shield allowed organisms to range over surface, exploiting new habitats and evolving diversity.

Front 17

Def: Phylogeny

Back 17

Evolutionary history of related DNA sequences.

Front 18

Carl Woese and the Tree of Life Pt. 1

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Universal tree of life (Figure 13.9) based on nucleotide sequence similarity in ribosomal RNA (rRNA).

Genealogy of all life on Earth.

Established the presence of three domains of life: Bacteria, Archaea, Eukarya.

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Carl Woese and the Tree of Life Pt. 2

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Root represents when all life shared the last universal common ancestor (LUCA).

Shows first life forms were microorganisms and that microbes have dominated most of history of life.

Front 20

Carl Woese and the Tree of Life Pt. 3

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Genomics supports three-domain concept through analysis of central cellular function genes.

Example: 60+ (including rRNA) genes shared by nearly all cells and must have been present in universal ancestor.

Of these, eukaryotic and archaeal genes share more similarity.

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Carl Woese and the Tree of Life Pt. 3

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Bacteria and Archaea likely diverged before Eukarya existed.

LUCA was likely prokaryotic with DNA genome and ability to transcribe and translate proteins.

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Carl Woese and the Tree of Life Pt. 4

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Carl Woese and the tree of life,other influences affecting phylogeny...

Many genes shared by two of three domains.

One hypothesis: Horizontal gene transfer was extensive before primary domains had diverged.

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Carl Woese and the Tree of Life Pt. 5

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Barriers likely evolved to maintain genomic stability.

Cells slowly sorted into primary lines of descent.

example: 60+ (including rRNA) genes shared by nearly all cells and must have been present in universal ancestor.

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Carl Woese and the Tree of Life Pt. 6

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Other influences affecting Phylogeny...

Bacteria and Archaea likely diverged ~3.7 billion years ago.

Eukarya diverged from Archaea ~1.2–2.7 billion years ago.

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Divergence of Eukarya from Archaea...

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... resulted in membrane-enclosed nucleus, and organelles gave rise to eukaryotic cell structures.

Front 26

Endosymbiosis Pt. 1

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Oxygen also spurred evolution of organelle-containing eukaryotic microorganisms.

Oldest eukaryotic microfossils ~ two billion years old.

Fossils of multicellular and more complex eukaryotes are found in rocks 1.9 to 1.4 billion years old.

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Endosymbiosis Pt. 2

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By 0.6 billion years ago, O2 was near present levels, and large multicellular organisms (Ediacaran fauna) were present in sea, then diversified into ancestors of algae, plants, fungi, animals.

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Endosymbiotic Hypothesis Pt. 1

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Well-supported hypothesis for origin of eukaryotic cells.

Contends that mitochondria arose from stable incorporation of an aerobic respiring bacterium into the cytoplasm of early eukaryotic cells.

Chloroplasts arose from stable incorporation of a cyanobacterium-like cell into cytoplasm of a eukaryotic cell, leading to eukaryotic photosynthesis.

Front 29

Endosymbiotic Hypothesis Pt. 2

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Oxygen spurred evolution of organelle-containing eukaryotic microorganisms.

Consumed by mitochondria, produced by chloroplast.

Physiology, metabolism, and genome structures/sequences of mitochondria and chloroplasts support endosymbiotic hypothesis.

70S ribosomes including 16S rRNA.

Mitochondria ancestor likely Alphaproteobacteria, chloroplast ancestor likely Cyanobacteria.

Front 30

Formation of the Eukaryotic Cell

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Eukaryotic cell is chimeric and made up of genes from both Bacteria and Archaea.

Eukaryotes have transcription and translational machinery similar to those of Archaea.

Eukaryotes have metabolisms similar to those of Bacteria.

Front 31

Two Hypotheses: Formation of the Eukaryotic Cell

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Serial Endosymbiosis Hypothesis

&

Symbiogenesis Hypothesis

Front 32

Serial Endosymbiosis Hypothesis Pt. 1

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Eukaryotes began as nucleus-bearing line that split from Archaea and later acquired mitochondria and chloroplasts by endosymbiosis.

Endosymbiosis occurred when line engulfed a bacterial cell that survived and replicated.

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Serial Endosymbiosis Hypothesis Pt. 2

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Eukaryotic genes that resemble bacterial genes were acquired through gene transfers from endosymbiont to nucleus.

Does not account for similarities in bacterial and eukaryotic membrane lipids.

Front 34

Symbiogenesis Hypothesis

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Eukaryotic cell arose from symbiotic relationship between Bacteria and Archaea; bacterial partner was engulfed to form mitochondria.

Front 35

Hydrogen Hypothesis

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Eukaryotic cell arose from an H2-producing bacterium and an H2-consuming Archaea.

Genes for lipid biosynthesis were transferred from bacterial symbiont to archaeal host.

Front 36

Origin of Nucleus

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Origin of nucleus unclear.

Formation may be associated with evolution of RNA processing (i.e., Nuclear membrane may have evolved to separate spliceosomes from ribosomes).

Front 37

Def: Evolution

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The change in allele (alternative version) frequencies in a population over time.

Front 38

Mutations

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Origins of genetic diversity.

Random changes in DNA sequence occurring over time.

Most mutations are neutral or deleterious; some are beneficial.

Several forms including substitutions, deletions, insertions, duplications.

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Def: Selection

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Selection is defined by fitness (ability of an organism to produce progeny and contribute to genetic makeup of future generations).

Front 40

Def: Genetic Drift

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Random process that can cause gene frequencies to change over time, resulting in evolution in the absence of natural selection.

Most powerful in small populations and those experiencing frequent “bottleneck” events.

Front 41

Evolution in Microorganisms

Back 41

New traits can evolve quickly in microorganisms.

Environmental change or introduction of new cells can cause rapid evolutionary changes.

Microbes form large populations and reproduce quickly.