1. Introduction to Microbiology Lecture 7
“Small creatures, big impacts”
Lecture 7

2. Introduction to Microbiology
Next lecture
Everyone should read the paper “Tree of Life”
11:10- 11:45:
Student evaluation
Open discussion and questions
Early ending if desired!
Introduction to Microbiology

3. Introduction to Microbiology
Lecture outline
Early Earth
Origin of life on Earth
Introduction to Microbiology

4. Early Earth and Origin of Life

5. Early Earth and Origin of Life
The Earth is ~ 4.5 billion years old
First evidence for microbial life : found in rocks ~ 3.86 billion years old??
Scanning Electron Micrograph of Microfossil Prokaryotes from 3.45 Billion Year old rocks of the Barberton Greenstone belt of South Africa
Early Earth and Origin of Life

6. Early Earth and Origin of Life
Stromatolites
Fossilized microbial mats
layers of filamentous prokaryotes and trapped sediment
Found in rocks 3.5 billion years old or younger
Comparisons of ancient and modern stromatolites:
Anoxygenic phototrophic filamentous bacteria formed ancient stromatolites (e.g. similar to Green non-sulfur Bacteria)
Oxygenic phototrophic cyanobacteria dominate modern stromatolites
Early Earth and Origin of Life

7. Conditions on early Earth
Anoxic
Surface temperatures of ~ 100ºC
Abundant methane, carbon dioxide, nitrogen and ammonia
Large reservoirs of sulfide (H2S and FeS)
Frequently bombarded by meteorites
Liquid water not possible
Liquid water accumulated after Earth cooled
Early life forms still heat tolerant
Early Earth and Origin of Life

8. The first biomolecules
Synthesis of biomolecules occurs spontaneously when gases and energy source present
Intense UV radiation (no ozone layer), lightning, radioactivity, heat from meteorite impacts, volcanic eruptions
Lab experiments-
Amino acids, nucleotides and fatty acids can form abiotically
Building blocks can polymerize
Degradation does not occur due to lack of life
Early Earth and Origin of Life

9. Urey-Miller experiment (1952)
Early Earth and Origin of Life

10. Early Earth and Origin of Life
Catalytic surfaces
Surfaces of clay or pyrite
Experiments with montmorillonite clay
Lipid vesicles form from fatty acids
Can enclose RNA
Early Earth and Origin of Life
Lipid vesicle
RNA

11. Early Earth and Origin of Life
The RNA world
Self replicating RNA
Catalytic RNAs (Ribozymes) catalyze several reactions including self replication
Eventually DNA and proteins evolved
DNA is more stable
Proteins are better catalysts (higher specificity)
Early Earth and Origin of Life

12. Surface origin hypothesis
Contends that the first membrane-enclosed, self-replicating cells arose out of primordial soup rich in organic and inorganic compounds in ponds on Earth’s surface
Dramatic temperature fluctuations and mixing from meteor impacts, dust clouds, and storms argue against this hypothesis
Early Earth and Origin of Life

13. Sub-surface origin hypothesis
States that life originated at hydrothermal springs 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
Early Earth and Origin of Life

14. Sub-surface origin hypothesis
Early Earth and Origin of Life

15. Primitive life: energy sources
No free oxygen: anoxic chemoautotrophs
Early Earth and Origin of Life

16. Primitive life: carbon sources
Likely C source: CO2 (abundant on early Earth)
Produce enough C from chemoheterotrophs
Autotrophic prokaryotes like Aquifex
Hyperthermophile
Contains small and simple genome
Branches near root of evolutionary tree
Early Earth and Origin of Life

17. Early Earth and Origin of Life
Molecular oxygen
Evolution of oxygenic photosynthesis
Cyanobacteria appeared ~ 2.8 Ga
Oxygen did not accumulate immediately due to large amounts of FeS
Early Earth and Origin of Life
Banded Iron Formation:
Alternating Iron-rich and silica rich layers

18. Early Earth and Origin of Life

19. Early Earth and Origin of Life
LUCA: Last Universal Common Ancestor
Population of early cells from which cellular life may have diverged into ancestors of modern day Bacteria and Archaea
Early Earth and Origin of Life

20. Endosymbiosis theory Early Earth and Origin of Life
Well-supported hypothesis for origin of eukaryotic cells
Contends that mitochondria and chloroplasts arose from symbiotic association of prokaryotes within another type of cell
More in paper “Tree of Life”
Early Earth and Origin of Life