Lecture 25-26: Microbial Ecology

What forms the foundation of Earth’s biosphere?

Microbial communities.

What do we mean when we say that microbes are ubiquitous?

They are found in every habitable environment and fill every potential niche imaginable.

What determines the ability of a microbe to fill a niche?

Microbial genome + environmental factors.

What is assimilation?

The process by which organisms acquire an element to build into cells.

What is dissimilation?

The process of breaking down organic nutrients to inorganic molecules.

What is a biomass?

Bodies of living organisms.

How do organisms obtain energy and materials for biomass?

By participating in the food web.

What are levels of consumption called?

Trophic levels.

What do food webs depend on primary producers for?

Absorbing energy from outside the ecosystem and assimilating minerals into biomass.

What are the two types of consumers?

Grazers and predators, microbes can be both.

What are bodies of dead organisms consumed by at each trophic level?

Decomposers.

Marine producers:

CO₂ fixation and biomass are performed by the phototrophic bacteria.

Marine consumers:

Protists and viruses.

Terrestrial producers:

Plants.

Terrestrial consumers:

Herbivores.

Lichens:

Fungus + (alga or cyanobacterium: sometimes both).

Rhizobium:

Inside leguminous (bean) plants.

Lichens Symbiotic Relationship:

Relationship between a fungal partner and a photosynthetic partner (green algae or cyanobacteria), mutualistic.

Rhizobia/Legume Interactions:

Rhizobia fix atmospheric nitrogen to ammonia and provide it to the plants, plants provide carbon source and shelter.

What are bacteroids?

Irregular shapes with no cell wall.

What is a Myxotricha paradoxa (multiple symbiont)?

A digestive symbiont of termites.

What is Myxotricha paradoxa?

A large ciliate (not bacteria) that grows in the guts of termites.

What types of symbionts does M. paradoxa have?

Bacterial endosymbionts-digest the cellulose found in wood.

What type of bacteria does M. paradoxa have?

Two spirochetes and two anchor bacteria.

What are the most common plant pathogens?

Fungi.

What do Ti plasmids do?

Induce tumor growth.

In the open ocean, what is the water column known as?

The pelagic zone.

Neuston (about 10 um):

Air-water interface.

Which zone has the highest microbe concentration?

The Neuston.

Euphotic zone (100-200 m):

Receives light, and so phototrophs grow.

Aphotic zone:

Only heterotrophs and lithotrophs can grow, below the reach of light.

What are benthos?

Ocean floor plus sediment below surface.

Benthic organisms:

Thermal vent communities.

Why are many prokaryotes from marine communities said to be uncultured?

We do not know their culture requirements.

What is metagenomics?

The analysis of total microbial community DNA, revealed approximately 25,000 different microbial species/liter seawater.

Where are mutualistic Zooxanthellae found?

In coral, algal symbionts.

What happens in coral bleaching?

Algal symbionts die or are expelled.

What is your microbiome?

Trillions of microorganisms living on and inside you.

What does the microbiome do?

Vitamin production, immune system development, digestion, and keeps out pathogens.

What is the microbiome made up of?

Mostly bacteria, also lots of archaea, fungi, and eukaryotes, as well as some viruses (especially bacteriophages).

How does the body control microbes?

Low pH (inhibits bacterial growth), bile salts (kill bacteria), and antimicrobial compounds produced in the gut.

How do we get a microbiome?

Infants are colonized by maternal vaginal and fecal microbes at birth.

The Human Genome Project:

They sequenced >11,000 samples in two phases and sequenced ~3,000 bacterial isolates.

What methods can be used to identify bacteria from a sample?

16S rRNA gene sequencing, whole genome sequencing, and metagenomic sequencing.

What is metagenomic “shotgun” sequencing useful for?

Identifying the functional potential of microbes.

Where can Clostridioides difficile Colitis (or diarrhea) be picked up?

Hospital environments or taking antibiotics.