Microbes 4 Key Concepts + Terms

What lineages did LUCA give rise to?

Archea and Bacteria, Eukaryotes later evolved from within Archaea group.

What information did LUCA have?

DNA genome, DNA polymerase, RNA polymerase, ribosomes, tRNAs

What is the Two-Domain Hypothesis?

Newer genomic data suggested eukaryotes evolved within archea. Asgard archea were discovered in deep sea hydrothermal vents (Loki’s Castle) and show complex cell shapes —> how eukaryotic complexity began. 

What is the basis of endosymbiotic theory?

That organelles such as mitochondria and chloroplasts originated as free living bacteria that were engulfed by another cell and then formed a symbiotic relationship.

What are the key evidences proving endosymbiotic theory?

Organelles look like bacteria (shape, size, membranes)

Molecularly, organelle DNA resembles bacterial DNA more than nuclear DNA

Genetically, many organelles were transferred to the host nucleus

What is HGT?

The exchange of genes between unrelated organisms, and makes evolution non tree like.

What are the types of HGT?

Transformation, Conjugation and Transduction

What is transformation?

What is conjugation?

What is transduction?

What is the Biological Species Concept?

“A group of individuals that can interbreed with one another but are reproductively isolated from other such groups.”

Species boundaries are maintained by barriers to gene flow (e.g., different mating systems, physical separation, or genetic incompatibility).

But microbes don’t “mate” sexually like animals — so scientists adapt this concept for bacteria and archaea.

Biological Species Concept in Microbes?

Gene flow still occurs through HGT, and microbial species under the BSC are groups of strains that exchange genes frequently with each other but rarely with members of other groups.

What are viruses?

Non-cellular infectious particles made of:

• Genome (DNA or RNA)

• Protein coat (capsid)

• Sometimes a lipid envelope

Why are viruses not cells?

They have no cytoplasm, ribosomes or metabolism. They also must hijack a host cell to reproduce.

What are phages? (Bacteriophages)

Viruses that infect bacteria or archea.

What are the ecological implications of phages?

Control bacterial populations, can transfer genes between cells (HGT), regulate blooms and pathogens

What is coevolution?

When two species change over time because they affect each other’s survival — like a virus evolving to infect a bacterium and the bacterium evolving to resist it. In other words, each one’s evolution causes the other to evolve too.

Explain phage therapy?

• Using lytic phages to kill antibiotic-resistant bacteria.

• Example: A 15-year-old patient with multi-drug-resistant infection was cured after screening >10,000 phages to find a match.

• Phages are highly specific — they target only certain bacteria.

Ecotype (or ecological) species concept?

A species concept in which species remain distinct due to adaptation to distinct
ecological niches, with selection within one niche having no effect on the other niche. There is little or no role for gene flow.