Chapter 01: The Evolution of Microorganisms and Microbiology

What are microorganisms?

Microorganisms are

• Organisms that are too small to be see by the unaided eye (<1 mm)

• Simple in construction

• Lack differentiated tissues

What are the two types of Microbial cells?

Prokaryotes (an “open floor plan”)

Eukaryotes (a “closed floor plan” w/ a membrane-enclosed nucleus)

Eukaryotes are larger and more morphologically complex compared to Prokaryotes.

What are the three classification schemes (domains) of life?

Bacteria, Archaea, & Eukarya

Classified via small subunit ribosomal ribonucleic acid (SSU rRNA)

What are some qualities of members of the Bacteria domain?

• Typically Single-celled

• Cell walls w/ Peptidoglycan

• Lack membrane-bound nucleus

• Live in extreme environments

• Can be either disease-causing or non disease-causing

What are some qualities of members of the Archaea domain?

• Are distinguished from Bacteria by having unique rRNA sequences

• Unique membrane lipids

• Some have unusual metabolic characteristics

• Live in extreme environments

• Doesn’t cause diseases directly in humans

What are some qualities of members of the Eukarya domain?

Split into two camps: protists and fungi

Protists:

• Unicellular but larger than Bacteria and Archaea.

  • Protozoa — animal-like metabolism

  • Algae — photosynthetic

Fungi:

• Unicellular or Multicellular

  • Yeast — unicellular

  • Molds & Mushrooms — multicellular

What is the central dogma of biology?

DNA → RNA → Proteins

DNA stores hereditary information

RNA acts as a messenger and takes DNA info and synthesizes proteins from it

Proteins can be structural or catalytic (enzymes)

What is the RNA World Hypothesis?

The RNA World Hypothesis is the idea that RNA was the original genetic molecule and the precursor of DNA.

Some evidence to support this is:

• RNA can regulate gene expression

• Energy source of current cells are ribonucleotides

• Most cellular RNA is associated with the ribosome (mRNA, tRNA, rRNA) to construct proteins

• rRNA catalyzes peptide bond formation in protein synthesis

What is LUCA?

Last Universal Common Ancestor

The LUCA is the most recent organism from which the three domains of life arose.

Archaea and Eukarya evolved independently from Bacteria but diverged from common ancestry a long time ago.

What is endosymbiosis and the endosymbiotic theory?

Endosymbiosis — the interaction between two organisms in which one lives inside of the other.

The endosymbiotic theory is that mitochondria, chloroplasts, and hydrogenosomes are endosymbiotic with eukaryotic cells. This is due to these organelles having similar DNA sequences and ribosomes to bacteria that is different from the eukaryotic nucleus.

Mitochondria — proteobacteria

Chloroplasts — prochloron

How do Bacteria, Archaea, and Eukarya evolve?

All three domains undergo random mutations.

Bacteria & Archaea — increase gene pool via Horizontal Gene Transfer (HGT; when the microbe sends its genetic information to its surrounding microbes; i.e. plasmids)

Eukarya — increase diversity via sexual reproduction

What are the three phyletic classification systems?

Microbial Phylogeny — the comparison of cell wall structure, biomolecules, and nucleotide sequences.

Phylogenetic Tree — displays the evolutionary relationship between organisms.

Universal Phylogenetic Tree — based on comparisons of SSU rRNA; aligned rRNA sequences from diverse organisms are compared and the differences are counted to derive a value of evolutionary distance. This is how relatedness (but not divergence) is determined.

How are phylogenetic trees built?

Built using a distance-based approach.

The differences in sequences are made into a statistic that can be used to determine evolutionary distance. The more sequence differences, the greater the evolutionary distance.

Who are some notable figures that contributed to the earliest microscopic observations?

Antony van Leeuwenhoek — the first person to observe microorganisms accurately using a “microscope”

Francesco Stelluti — observed bees and weevils

Robert Hooke — published drawings of the fungus Mucor in his book

Who was Louis Pasteur and describe his Swan-Necked Flask Experiments.

Louis Pasteur was an important microbiologist that demonstrated microorganisms carried out fermentation. He helped the French wine industry by developing the technique of pasteurization to avoid wine spillage by microbes.

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Pasteur’s Swan Neck experiment was done to disprove spontaneous generation of life.

He did this by first heating up two flasks to kill all of the microbes living inside of the flasks

Then, he added sterile broth to both flasks to give any potential microbes ample resources to grow an populate.

Next, Pasteur broke one of the necks of the flasks directly over the opening of the flask chamber while keeping the other swan flask intact.

After waiting some time, Pasteur found that the broken flask had microbial growth occurring, whereas the unbroken swan flask had no microbial growth.

This is because airborne microbes could not fight gravity to go up the swan neck flask and was stuck at the base of the neck, resulting in no microbes reaching the broth. For the broken flask, however, the airborne microbes could get in through the opening, resulting in growth. Thus, Pasteur showed that spontaneous generation of microbes was not true.

Who was Robert Koch and describe his four postulates and limitations of such postulates.

Robert Koch was a microbiologist who established the relationship between Bacillus anthracis and anthrax. He also demonstrated that Mycobacterium tuberculosis causes Tuberculosis (TB). He also developed 4 postulates to help determine whether a microorganism causes disease.

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1. Microorganism must be present in every infected organisms but not in non-infected.

2. The microorganism needs to be isolated from an infected organism and grown in pure culture.

3. The isolated microorganism must cause the same disease when a healthy organism is infected with the microorganism.

4. The same microorganism must be able to be isolated again from the newly infected host of postulate 3.

Limitations:

• Some microorganisms can’t be grown in pure culture.

• There is no animal model to use to simulate a human when infected by the microorganism.

• It is unethical to use humans when completing the postulates.