Bacteria and Archaea

Chapter 20

Prokaryotes

Organisms in the domains Bacteria and Archaea that lack a true nucleus.

Main prokaryotic domains

Bacteria and Archaea.

Prokaryotic cell size

About 1–10 μm in length.

Three regions of a prokaryotic cell

Cell envelope, cytoplasm, and appendages.

Cell envelope

The structures surrounding the cytoplasm, including the plasma membrane, cell wall, and glycocalyx.

Plasma membrane

A phospholipid bilayer that surrounds the cell.

Cell wall

A support structure outside the plasma membrane that helps prevent the cell from bursting.

Glycocalyx

A polysaccharide layer, sometimes containing protein, that surrounds many prokaryotes.

Functions of the glycocalyx

Protects cells, helps hold colonies together, forms biofilms, and helps with communication.

Cytoplasm

The fluid and structures inside the plasma membrane.

Nucleoid region

The region containing the prokaryote's single large, looping chromosome.

Plasmid

A small loop of DNA separate from the main chromosome.

Thylakoids

Folded regions of the plasma membrane in some bacteria that increase surface area for processes such as photosynthesis.

Fimbriae

Hairlike bristles used by prokaryotes to attach to surfaces.

Conjugation pilus

A long, hollow structure used by prokaryotes to exchange DNA.

Flagella

Structures that rotate and propel prokaryotic cells.

Binary fission

An asexual form of prokaryotic reproduction in which one cell divides into two cells.

Conjugation

Genetic recombination in which two prokaryotic cells exchange DNA through a pilus.

Transformation

Genetic recombination in which a prokaryotic cell takes in DNA from its surroundings.

Transduction

Genetic recombination in which a virus or another mechanism inserts DNA into a prokaryotic cell.

Bacterial cell wall

A cell wall containing peptidoglycan that helps prevent bacterial cells from rupturing.

Peptidoglycan

A molecule found in bacterial cell walls.

Gram stain

A test used to determine the amount of peptidoglycan in a bacterial cell wall.

Gram-positive bacteria

Bacteria with a thick peptidoglycan layer that retain the violet color during a Gram stain.

Gram-negative bacteria

Bacteria with less peptidoglycan and a thin outer membrane; they lose the violet stain and retain the pink color.

Gram-positive vs. Gram-negative

Gram-positive bacteria have thick peptidoglycan and stain purple; Gram-negative bacteria have less peptidoglycan, an outer membrane, and stain pink.

Three common bacterial shapes

Spiral-shaped, rod-shaped, and spherical.

Spirilli

Spiral-shaped bacteria.

Bacilli

Rod-shaped bacteria.

Cocci

Spherical bacteria.

Obligate aerobes

Organisms that cannot grow without free oxygen.

Obligate anaerobes

Organisms that cannot grow in the presence of free oxygen.

Facultative anaerobes

Organisms that can grow with or without free oxygen.

Photoautotrophs

Organisms that use light energy to convert inorganic CO2 into organic molecules.

Chemoautotrophs

Organisms that use energy from inorganic compounds to convert inorganic CO2 into organic molecules.

Chemoheterotrophs

Organisms that break down organic materials for carbon and energy.

Saprotrophs

Organisms that obtain nutrients by decomposing organic material from dead organisms.

Symbiosis

An interaction in which two organisms are dependent on each other for some function.

Mutualism

A relationship in which both organisms benefit.

Commensalism

A relationship in which one organism benefits while the other is neither helped nor harmed.

Parasitism

A relationship in which one organism benefits at the expense of the other.

Pathogen

A disease-causing parasite or organism.

Endospore

A dormant cell surrounded by a thick protein coat that allows some bacteria to survive unfavorable conditions.

Biofilm

A colony of microorganisms held together by a glycocalyx.

Why are biofilms important?

They allow prokaryotic cells to stay together, communicate, and gain protection.

Cyanobacteria

Photoautotrophic Gram-negative bacteria that are thought to be the original photosynthesizers.

Cyanobacteria and chloroplasts

Cyanobacteria lack chloroplasts but have pigments that capture light for photosynthesis.

Cyanobacteria and lichens

Cyanobacteria can form mutualistic relationships with fungi to create lichens.

Archaea

A prokaryotic domain whose members lack peptidoglycan and have branched membrane phospholipid tails.

Why are Archaea different from Bacteria?

Archaea have different ribosomal RNA sequences, lack peptidoglycan, and have branched membrane phospholipid tails.

Extremophile

An organism that prefers environmental conditions that are too harsh for most organisms.

Halophile

An archaeon that prefers environments with high salt concentrations.

Thermoacidophile

An archaeon that prefers extremely hot and acidic environments.

Thermoacidophile habitat

They can live in environments such as geysers and volcanic vents.

Methanogen

An archaeon that produces methane (CH4) as a metabolic by-product.

Archaea in moderate environments

Not all Archaea are extremophiles; some live in moderate environments.