Evolution & Evolution & ClassificationClassificationof Microbesof Microbes

Unit 10Unit 10

Donna HowellDonna Howell

Medical MicrobiologyMedical Microbiology

Blacksburg High SchoolBlacksburg High School

What is a Prokaryote?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.

Evolution of MicrobesEvolution 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.

Evolution of MicrobesEvolution 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.

First Living OrganismsFirst 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!

Evolution of MicrobesEvolution 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.

Evolution of MicrobesEvolution 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.

Evolution of MicrobesEvolution 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.

Evolutionary Time LineEvolutionary Time Line

Carl Woese’s Tree of LifeCarl Woese’s Tree of Life

What is a Eukaryote?What is a Eukaryote?

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

Eukaryotic EvolutionEukaryotic 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.

Endosymbiotic TheoryEndosymbiotic 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.

Endosymbiotic TheoryEndosymbiotic 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.”

Endosymbiotic TheoryEndosymbiotic 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

Endosymbiotic TheoryEndosymbiotic Theory

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

Binomial NomenclatureBinomial Nomenclature

• The correct way to write an organism’s name is:– Genus, then

species– Whole name

italicized– Genus capitalized,

species not capitalized

Canis lupus

Viral NomenclatureViral NomenclatureThe 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.

Evolution on Fast ForwardEvolution on Fast ForwardAs 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.

Vertical Gene TransferVertical Gene Transfer

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

Horizontal Gene TransferHorizontal Gene TransferWhen 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.

The Success of Microbes!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.

The End!The End!Doesn’t all

that give you warm fuzzies

all over?