Lec 19: Microbes

Microbe

tiny living thing

so not based on lineage, just small living shit

Types of Microbes

bacteria (cyanobacteria and most prokaryotes)

some eukaryotes (protists [all eukaryotes that are not animals, fungi, or land plants], animals, fungi, and most algae)

archaea (extremophiles, love places too extreme for other animals)

What do bacteria and archaea have in common?

they are prokaryotes, small cells without a nucleus or specialized organelles

How do most bacteria/archaea reproduce?

By binary fission

Are bacteria and archaea from the same lineage?

NO

T or F: Are eukaryotes nested within archaea?

True

Endosymbiont hypothesis

Eukaryotic mitochondria and chloroplasts were once separate prokaryotic microbes

Key cell structure differences between prokaryotes and eukaryotes

Prokaryotes: lack membrane-bound organelles, DNA not enclosed in a nucleus

Eukaryotes: membrane-bound organelles, DNA enclosed in nuclei

Key size differences between prokaryotes and eukaryotes

prokaryotes are usually smaller

Key reproductive differences between prokaryotes and eukaryotes

Prokaryotes: reproduce asexually through binary fission

Eukaryotes: reproduce both asexually and sexually

Key genetic differences between prokaryotes and eukaryotes

Pro: single circular chromosome, often contain additional small DNA molecules called plasmids

Euk: multiple linear chromosomes contained within the nucleus

Archaea

generally extremophiles with anaerobic metabolisms (must occur in places without oxygen)

found in harsh anoxic (total lack of oxygen) environments of extreme salinity or temp (animal guts, in ice, etc.)

T or F: some archaea are chemoautotrophs that live in volcanic vents where water is rich in hydrogen sulfide

True

Methanogens

archaea that produce methane as a byproduct

Bacteria

Highly diverse group that contains species that live by every mode of nutrition and metabolism possible

T or F: some bacteria are parasites

T or F: some bacteria are pathogens

T or F: some bacteria decompose organic matter

T or F: some bacteria are symbionts in animal guts

True for all

Oxygenic photoautotrophs

oxygen-releasing photosynthesis

Anoxygenic photoautotrophs

photosynthesis without producing oxygen

T or F: cyanobacteria are oxygenic photoautotrophs and not anoxygenic photoautotrophs

False, they can be either

Define these word-pieces

Photo-

Chemo-

-autotroph

-heterotroph

Photo: photosynthesis, energy from sunlight

Chemo: Energy from chemical reactions

autotroph: carbon from CO2

heterotroph: carbon from organic molecules

What ____troph are humans?

Chemoheterotroph

What ____troph is this?
Only grows in darkness, and when glucose is supplied

Chemoheterotroph

What changes as you move down a gradient (ancient mats, dental biofilms, host microbiomes)?

Oxygen decreases, light decreases, available energy sources change

What is the gradient of a microbial mat from atmosphere to sediment?

Cyanobacteria (oxygenic photosynthesis)

Aerobic heterotrophs (use O2 and organic carbon)

Fermenters (low O2 and organic carbon)

Anaerobes (sulfur, methane, nitrate chemistry)

How did cyanobacteria change the chemistry of Earth?

Its waste product (oxygen) became a global environment variable

It was the first bump in the wave of oxygen in Earth (second bump is land plants!)

Oxygenation affect on Anaerobes

O2 can be toxic, so many lineages persist where O2 is low

Oxygenation affect on aerobes

O2 enables high-energy metabolism in many organisms

Oxygenation affect on eukaryotic complexity

Mitochondria and aerobic metabolism support larger cells

Oxygenation affect on new ecosystems

Oxygen gradients create new niches and interactions

Did oxygenic photosynthesis transform environmental chemistry before or after complex life diversified?

Before, necessary for the diversification

Microbiome

Ecosystem inside or on a host (host being a habitat, resource provider, selective environment, or participant)

What factors can differ across microbiomes?

Community composition: which taxa are present and how abundant

Disturbance: what changes after antibiotics, diet shifts, disease, etc.

Community function: what metabolites or signals are produced?

Causality: does the community CAUSE an outcome/respond to it, or both?

How to establish causality

Through an experiment, using controls

How do microbiomes affect their hosts?

Disturbance to microbiome (antibiotic, diet, infection) —> [Possible Restoration (intervention)] —> Community shift (taxa change in abundance) —> Function shift (metabolites and signals change) —> Host outcome (symptoms, inflammation, recovery)