Lesson 1: A Microbial Planet

What is the general definition of a microbe?

A free-living organism that can only be seen under a microscope, typically <100 μm, although exceptions exist

Why is Chlamydia trachomatis an exception to the general definition of a microbe?

It is not free-living; it is an obligate intracellular pathogen that cannot replicate outside host cells

Why does the professor not consider viruses microbes/living organisms?

They are acellular, cannot replicate independently, and cannot perform their own metabolism

What is the general size order from smallest to largest?

Viruses → bacteria → unicellular eukaryotes (such as yeast) → larger microbes

What is an example of an unusually large microbe?

Epulopiscium fishelsoni; it can reach 200–700 μm

What are the major bacterial shapes?

Coccus = sphere; Bacillus = rod; Vibrio = curved rod; Coccobacillus = between sphere and rod; Spirillum = thick and rigid spiral; Spirochete = thin and flexible corkscrew

Why are spirochetes good at moving through viscous environments?

Their thin, flexible corkscrew shape allows movement through substances like mucus and mud

What diseases are associated with the spirochetes discussed in lecture?

Borrelia burgdorferi → Lyme disease; Treponema pallidum → syphilis

What organisms are prokaryotes?

Bacteria and Archaea

What is the key difference between prokaryotic and eukaryotic cells?

Prokaryotes lack a true membrane-bound nucleus and membrane-bound organelles; eukaryotes have them

What is a nucleoid?

The non-membrane-bound region containing the genome of a prokaryotic cell