1. Evolution & Classification of Microbes Unit 10
Donna Howell
Medical Microbiology
Blacksburg High School

2. What is a Prokaryote?
A prokaryote is an organism whose cells do NOT have a nucleus – the only organisms in this group are the Archaea and the Bacteria.

3. Evolution of Microbes
Hard to find evidence of microbes in fossil record – they do not have bones, so do not preserve well.
Wasn’t until the 1960’s that we really began studying microbial evolution due to limitations in technique.

4. Evolution of Microbes
In 1965, scientists found fossilized remnants of microbes in rocks dated to 2 billion years ago.
Oldest evidence of microbial life is in rocks that date to 3.5 billion years ago.

5. First Living Organisms
Scientists estimate that the world is about 4.5 billion years old. Bacteria are estimated to have been around 3.5 billion of these years! Eukaryotes would not appear for 2 million years!

6. Evolution of Microbes
Scientists believe that an early photosynthetic bacterium, Cyanobacterium, was responsible for changing the Earth’s early atmosphere from one of methane, carbon dioxide, nitrogen, and ammonia to one of oxygen.

7. Evolution of Microbes
When DNA was discovered, microbes began to be classified. By comparing the number of mutations in DNA, scientists could deduce how closely related two microbes were.

8. Evolution of Microbes
Carl Woese of University of Illinois created a new universal “tree of life” by analyzing ribosomal RNA.
He divided it into three main branches: Archaea, Bacteria, and Eukarya.

9. Evolutionary Time Line

10. Carl Woese’s Tree of Life

11. What is a Eukaryote?
A eukaryote is an organism whose cells DO have a nucleus – this includes the protists, fungi, plants and animals.

12. Eukaryotic Evolution
About 1 billion year ago, scientists believe that complex cells began to evolve.
In response to evolutionary pressure, these new cells began to evolve new things to keep cells running smoother, such as a nucleus, organelles, and sexual reproduction.

13. Endosymbiotic Theory
Scientists realized that certain organelles (mitochondria, chloroplast) inside eukaryotic cells resembled prokaryotes.
They hypothesized that bacteria “took up residence” inside cells and formed a symbiotic relationship.

14. Endosymbiotic Theory
How did Eukaryotes arise? Lynn Margulis believes they came from prokaryotes. “Larger bacterial cells lost their cell walls and engulfed smaller bacterial cells, which became the nucleus.”

15. Endosymbiotic Theory
Mitochondria remind scientists of bacteria for the following reasons:
Have own DNA in circular form
Own RNA and ribosomes for protein synthesis
Divide by binary fission

16. Endosymbiotic Theory
It is believed that chloroplasts were once Cyanobacteria that were eaten by another cell, and a symbiotic relationship between the two resulted.

17. Binomial Nomenclature
The correct way to write an organism’s name is:
Genus, then species
Whole name italicized
Genus capitalized, species not capitalized
Canis lupus

18. Viral Nomenclature
The only exception to this naming rule is the viruses, which are not considered to be living things. They are called by their common name, i.e. Hantavirus.

19. Evolution on Fast Forward
As scientists tried to construct the tree of life for bacteria, it was difficult because they had conflicting data. It was generally assumed, until this point, that genes were ONLY transferred from parent to offspring. But the microbes had a surprise in store for us! Microbes have TWO methods of gene transfer.

20. Vertical Gene Transfer
When genes are passed from one microbe to another through the normal division process – binary fission.

21. Horizontal Gene Transfer
When microbes pass genes to their neighboring microbes, like handshaking! A microbe can take DNA from another microbe in a few ways (discussed next unit), thereby gaining new genes and therefore new capabilities.

22. The Success of Microbes!
The two phenomena most responsible for the enormous biologic success of microbes on our planet are: 1) the ability to reproduce so quickly and 2) the ability to share genes.

23. Doesn’t all that give you warm fuzzies all over?
The End!
Doesn’t all that give you warm fuzzies all over?