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

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

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

Early Earth and Origin of Life

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

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

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

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

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

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

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

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

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

Sub-surface origin hypothesis Early Earth and Origin of Life

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

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

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

Early Earth and Origin of Life

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

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