Diversity of Microbes Chapter 13 Part 1

What are microbial mats?

Microbial mats are layered sheets of microorganisms growing together.

Characteristics:

• Mostly bacteria

• Some archaea

• Several centimeters thick

• Grow in moist environments

• Among the earliest ecosystems on Earth

Where were the first microbial mats likely found?

Near deep-sea hydrothermal vents.

They obtained energy from chemicals released by the vents before photosynthesis evolved.

How did microbial mats change after phototrophs evolved?

Phototrophic microbes could use sunlight instead of vent chemicals.

This allowed microbial mats to spread into shallow waters and across much of Earth.

What are stromatolites?

Stromatolites are layered sedimentary rock structures formed when microbial mats trap sediments and minerals.

Most stromatolites are fossils, but some are still living today.

Why are stromatolites important?

They provide some of the oldest fossil evidence of life on Earth.

Many are over 3 billion years old.

What are extremophiles?

Extremophiles are microorganisms that live in environments most organisms cannot survive.

Examples include:

• Very hot

• Very cold

• Extremely salty

• Highly acidic

• Highly alkaline

Why are extremophiles important to evolutionary biology?

They may resemble some of Earth's earliest life forms because early Earth had similarly harsh conditions.

What is a biofilm?

A biofilm is a community of microorganisms attached to a surface and embedded in a sticky extracellular matrix.

Biofilms often contain many different microbial species.

What is the extracellular matrix of a biofilm made of?

Mostly polysaccharides (sugars).

It helps microbes:

• Stick together

• Attach to surfaces

• Resist drying

• Resist chemicals and antibiotics

Where are biofilms commonly found?

occur almost everywhere:

• Rocks

• Streams

• Lakes

• Ocean docks

• Water pipes

• Sewage treatment plants

• Household surfaces

• Medical devices

• Dental plaque

Why do bacteria prefer living in biofilms?

Biofilms provide:

• Protection from predators

• Protection from antibiotics

• Better nutrient access

• Improved survival

• Easier communication between cells

What structures do all cells (prokaryotic and eukaryotic) have?

Every cell contains:

• Plasma membrane

• Cytoplasm

• DNA

• RNA

• Ribosomes

What are the three major bacterial shapes?

1. Cocci = spherical

2. Bacilli = rod-shaped

3. Spirilla = spiral-shaped

Memory Trick: CBS

• Cocci = Circle

• Bacilli = Bar (rod)

• Spirilla = Spiral

What is the function of the bacterial cell wall?

The cell wall:

• Maintains shape

• Prevents bursting

• Protects the cell

In bacteria, it is made of peptidoglycan.

What is peptidoglycan?

A strong material made of:

• Sugars

• Short protein chains

It forms bacterial cell walls.

Only bacteria have peptidoglycan.

How are archaeal cell walls different from bacterial cell walls?

Archaea do not contain peptidoglycan.

Their cell walls are made from different materials.

What is a bacterial capsule?

A sticky protective layer outside the cell wall.

Functions:

• Prevents dehydration

• Helps bacteria attach to surfaces

• Protects against immune cells

What is the nucleoid?

The nucleoid is the region containing the bacterial chromosome.

Characteristics:

• No membrane

• Circular chromosome

• Not a true nucleus

What is the function of flagella?

Flagella provide movement.

They allow bacteria to swim toward nutrients or away from harmful substances.

How do prokaryotes reproduce?

By binary fission.

One cell divides into two genetically identical daughter cells.

What are the steps of binary fission?

1. DNA replicates.

2. Cell elongates.

3. Plasma membrane pinches inward.

4. Cell wall forms.

5. Two identical daughter cells separate.

Why can bacterial populations grow so quickly?

Some bacteria divide every 20 minutes.

Each division doubles the population.

Example:

1 → 2 → 4 → 8 → 16 → 32...

Do bacteria exchange genetic material?

Yes.

Although binary fission produces identical cells, bacteria also exchange DNA.

What are the three methods of bacterial genetic recombination?

1. Transformation

2. Transduction

3. Conjugation

What is transformation?

A bacterium picks up free DNA from its environment.

What is transduction?

DNA is transferred from one bacterium to another by a virus (bacteriophage).

What is conjugation?

DNA is transferred directly between bacteria through a pilus.

Often called bacterial "mating."

Why do bacteria stain Gram-positive or Gram-negative?

Because of differences in their cell walls, especially the thickness of peptidoglycan.

What is a chemotroph?

A chemotroph obtains energy from chemical compounds instead of sunlight.

What is a phototroph?

A phototroph obtains energy from sunlight.

What is a pathogen?

A microorganism that causes disease.

Examples:

• Bacteria

• Viruses

• Fungi

• Protists

What is the difference between an epidemic and a pandemic?

Epidemic

Disease spreads through one region or population.

Pandemic

Disease spreads across multiple countries or worldwide.

What is the bubonic plague?

A bacterial disease caused by Yersinia pestis.

It caused one of history's deadliest pandemics.

What are antibiotics?

Medicines that kill bacteria or stop bacterial growth.

Many antibiotics are naturally produced by fungi or bacteria.

What causes antibiotic resistance?

Natural selection caused by antibiotic overuse.

Examples:

• Not finishing prescriptions

• Unnecessary antibiotic use

• Antibiotics in livestock

Resistant bacteria survive and reproduce.

What is MRSA?

Methicillin-Resistant Staphylococcus aureus

A strain of bacteria resistant to many antibiotics.

How are prokaryotes used in food production?

Bacteria help produce:

• Yogurt

• Cheese

• Vinegar

• Soy sauce

• Salami

What is bioremediation?

The use of microorganisms to remove pollutants from the environment.

Examples:

• Oil spill cleanup

• Sewage treatment

• Waste decomposition

How do bacteria clean oil spills?

Some bacteria use hydrocarbons (oil) as an energy source, breaking the oil down into simpler substances.

What is normal microbiota (normal flora)?

The microorganisms that normally live on and inside the human body.

Locations include:

• Skin

• Mouth

• Gut

• Nose

• Urinary tract

Why is normal microbiota beneficial?

Normal microbiota:

• Compete with pathogens

• Aid digestion

• Produce vitamins

• Support immune function

When did prokaryotes first appear?

Approximately 3.5 billion years ago.

When did eukaryotes evolve?

About 2.1 billion years ago.

They evolved long after prokaryotes.

How did membrane-bound organelles first evolve?

The plasma membrane folded inward, forming structures such as:

• Nucleus

• Endoplasmic reticulum

• Lysosomes

What is endosymbiosis?

A process where one organism lives inside another in a mutually beneficial relationship.

This explains the origin of mitochondria and chloroplasts.

How did mitochondria evolve?

An ancestral eukaryotic cell engulfed an aerobic bacterium.

Instead of being digested, it became a mitochondrion.

How did chloroplasts evolve?

A eukaryotic cell engulfed a cyanobacterium.

The cyanobacterium evolved into a chloroplast.

Which evolved first: mitochondria or chloroplasts?

Mitochondria

All eukaryotes have mitochondria (or evolved from ancestors that did), but only plants and algae have chloroplasts.

What evidence supports the endosymbiotic theory?

Mitochondria and chloroplasts:

• Have their own circular DNA

• Have bacterial-like ribosomes

• Reproduce by binary fission

• Have double membranes

• Are similar in size to bacteria

Why do mitochondria and chloroplasts have two membranes?

• Inner membrane: from the original bacterium.

• Outer membrane: from the host cell that engulfed it.

This supports endosymbiosis.

The first forms of life on Earth were:

Prokaryotes

The organisms that first oxygenated Earth's atmosphere were:

Cyanobacteria

Which domains contain prokaryotic cells?

Bacteria and Archaea

Gram staining depends primarily on differences in the ______.

Cell wall

Organisms obtaining energy from chemicals are called:

Chemotrophs

True or False: Every generation of bacteria is always genetically identical.

False

Bacteria exchange DNA through:

• Transformation

• Transduction

• Conjugation

True or False: Bacteria can exchange genetic material.

True

Bioremediation is the use of microorganisms to:

Clean up pollutants

What event helped eukaryotes evolve?

Oxygenation of Earth's atmosphere

Mitochondria most likely evolved from:

Aerobic bacteria

Microbial mats

earliest layered microbial communities.

Stromatolites

fossilized microbial mats.

Extremophiles

microbes living in extreme environments.

Biofilms

communities of microbes attached to surfaces in a sticky matrix.

Three bacterial shapes

Cocci, Bacilli, Spirilla (CBS).

Peptidoglycan

found only in bacterial cell walls.

Binary fission

produces two genetically identical daughter cells.

Genetic recombination occurs

by Transformation, Transduction, and Conjugation (TTC).

Antibiotic resistance

evolves through natural selection.

Bioremediation

uses microbes to clean pollutants.

Normal microbiota

protect against pathogens and aid health.

Endosymbiotic theory

Mitochondria evolved from aerobic bacteria; chloroplasts evolved from cyanobacteria.

Evidence for endosymbiosis

circular DNA, bacterial ribosomes, binary fission, double membranes, and bacterial size.

What are microorganisms?

Microorganisms (microbes) are organisms that are too small to be seen clearly with the naked eye.

Most require a microscope to observe.

Examples include:

• Bacteria

• Archaea

• Many protists

• Some fungi

• Some microscopic animals

In which three domains are microorganisms found?

Microorganisms occur in all three domains of life:

1. Bacteria → bacteria

2. Archaea → archaea

3. Eukarya → some fungi, protists, and microscopic animals

Which microorganisms are eukaryotes?

Eukaryotic microorganisms include:

• Protists

• Many fungi (such as yeasts)

• Some microscopic animals

They have:

• A nucleus

• Membrane-bound organelles

Which microorganisms are prokaryotes?

Prokaryotic microorganisms include:

• Bacteria

• Archaea

They lack:

• A nucleus

• Membrane-bound organelles

What is a prokaryote?

A prokaryote is an organism whose cells do not have:

• A nucleus

• Mitochondria

• Golgi apparatus

• Endoplasmic reticulum

• Other membrane-bound organelles

DNA is located in the nucleoid region.

Why were bacteria and archaea originally classified together?

Both have:

• Prokaryotic cells

• No nucleus

• No membrane-bound organelles

Scientists originally grouped them into one kingdom because of these similarities.

Why are bacteria and archaea now placed in separate domains?

DNA and molecular studies revealed major differences in:

• Genetics

• Cell membranes

• Cell walls

• Ribosomal RNA

• Biochemistry

Although both are prokaryotes, they evolved separately.

How old is Earth?

Earth formed approximately 4.54 billion years ago.

What were conditions like on early Earth?

Early Earth was extremely harsh.

Characteristics included:

• No oxygen (anoxic atmosphere)

• High volcanic activity

• Intense ultraviolet radiation

• Extremely high temperatures

• Frequent meteor impacts

Only specialized organisms could survive.

What does "anoxic atmosphere" mean?

An anoxic atmosphere contains little or no oxygen (O₂).

Early Earth's atmosphere could not support modern oxygen-dependent organisms.

What kinds of organisms were the first living things?

The earliest organisms were:

• Simple

• Single-celled

• Prokaryotic

• Anaerobic

They survived without oxygen.

What is an anaerobic organism?

An anaerobic organism can:

• Live

• Grow

• Reproduce

Without oxygen.

Some oxygen is actually toxic to these organisms.

Why couldn't early organisms rely on oxygen?

Because oxygen did not yet exist in Earth's atmosphere.

Life evolved before oxygen became abundant.

Where may the first life have originated?

Scientists think early life may have developed in protected environments such as:

• Deep oceans

• Hydrothermal vents

• Warm underwater environments

These areas protected organisms from harmful UV radiation.

Why were hydrothermal vents good locations for early life?

Hydrothermal vents provided:

• Heat

• Minerals

• Chemical energy

• Protection from UV radiation

These conditions may have supported the earliest microorganisms.

What is a phototroph?

A phototroph is an organism that converts light energy into chemical energy.

Light is used to produce energy for cellular processes.

What were anaerobic phototrophs?

Anaerobic phototrophs were early organisms that:

• Used sunlight for energy

• Did not require oxygen

They were among the first organisms on Earth.

What are cyanobacteria?

Cyanobacteria are photosynthetic bacteria that:

• Use sunlight

• Use carbon dioxide

• Release oxygen

They transformed Earth's atmosphere.

Why are cyanobacteria important in evolution?

Cyanobacteria produced oxygen through photosynthesis.

This changed Earth's atmosphere forever and allowed aerobic organisms to evolve.

What process do cyanobacteria perform?

Photosynthesis

Overall reaction:

Carbon dioxide + Water + Sunlight → Glucose + Oxygen

What gas is released during photosynthesis?

Oxygen (O₂)

This oxygen gradually accumulated in Earth's atmosphere.

How did photosynthesis change Earth?

Photosynthesis:

• Increased atmospheric oxygen

• Reduced carbon dioxide

• Allowed aerobic organisms to evolve

• Changed Earth's climate and ecosystems

What are aerobic organisms?

Aerobic organisms require oxygen for cellular respiration.

They evolved only after oxygen became abundant.

Which evolved first: anaerobic or aerobic organisms?

Anaerobic organisms

Reason:

There was no oxygen on early Earth.

Aerobic organisms evolved later after cyanobacteria increased oxygen levels.

Compare anaerobic and aerobic organisms.

Anaerobic

• Do not require oxygen

• First organisms on Earth

• Oxygen may be toxic

Aerobic

• Require oxygen

• Evolved later

• Produce much more ATP during respiration

Compare prokaryotic and eukaryotic cells.

Prokaryotes

• No nucleus

• No membrane-bound organelles

• Smaller

• Simpler

Examples:

• Bacteria

• Archaea

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Eukaryotes

• Nucleus present

• Membrane-bound organelles

• Larger

• More complex

Examples:

• Animals

• Plants

• Fungi

• Protists