Ch 27: Prokaryotes - Bacteria and Archaea
• Prokaryotes are divided
into two domains
– bacteria and archaea
• thrive in diverse habitats
– including places too acidic,
salty, cold, or hot for most
other organisms
• Most are microscopic
– but what they lack in size
they make up for in
numbers
– For example: more in a
handful of fertile soil than
the number of people who
have ever lived
Great Salt Lake – pink color
from living prokaryotes;
survive in 32% salt
Prokaryotes
• Single cell
– Some form colonies
• Very small
– 0.5–5 µm (10-20 times smaller
than Eukaryotes)
• Lacks nucleus and most other
membrane bound organelles
• Reproduce very quickly
– Asexual binary fission
– Genetic recombination
• variety of shapes
– spheres (cocci)
– rods (bacilli)
– spirals
• Cell wall
More structural & functional characteristics in (Ch.27)
Bacilli
• Rod shaped
– Example: E. coli
• Usually solitary
• Sometimes chains
– streptobacilli
Cocci
• Spherical
– Clumps or clusters (like
grapes)
• E.g. Staphylococcus aureus
– Streptococci – chains of
spheres
– Diplococci – pairs of
spheres
• E.g. Neisseria gonnorheae
Streptococcus 1
Streptococcus 2
Diplococcus 1
Diplococcus 2
Spiral prokaryotes
• Spirilla – spiral shaped
– With external flagella
– Variable lengths
• Spirochaetes
– Internal flagella
– Corkscrew-like
• Boring action
• E.g. Treponema pallidum (Syphilis)
Cell-Surface Structures
• Cell wall is important
– maintains cell shape
– protects the cell
– prevents it from bursting in a
hypotonic environment
• Eukaryote cell walls are
made of cellulose or chitin
• Bacterial cell walls contain
peptidoglycan
– network of sugar polymers
cross-linked by polypeptides
• Archaea cell walls
– polysaccharides and proteins
but lack peptidoglycan
• Scientists use the Gram stain to classify bacteria by cell
wall composition
– Counter stains to differentiate between cell wall
characteristics
Gram-positive
bacteria
Gram-negative
bacteria
10 m
– Gram-positive bacteria
• simpler walls with a large amount of peptidoglycan
– Gram-negative bacteria
• less peptidoglycan and an outer membrane that can be toxic
Gram positive bacteria
• Thick layer of
peptidoglycans
• Retains crystal violet
– Doesn’t wash out
– Masks red safranin
• Stains dark purple or
blue-black
Gram negative
bacteria
• Thin sandwiched layer
of peptidoglycans
• Rinses away crystal
violet
• Stains pink or red
(b) Gram-negative bacteria: crystal violet is easily rinsed
away, revealing red dye.
Carbohydrate portion
of lipopolysaccharide
Outer
membrane
Cell
wall Peptidoglycan
layer
Plasma membrane
• Extra capsule covers
many prokaryotes
Bacterial
cell wall
– polysaccharide or protein
layer
Bacterial
capsule
Tonsil
cell
• Some also have fimbriae
– stick to substrate or other
individuals in a colony
• Pili (or sex pili)
– longer than fimbriae
– allow prokaryotes to
exchange DNA
200 nm
Fimbriae
1 m
Diverse nutritional and metabolic adaptations have
evolved in prokaryotes
• Prokaryotes can be categorized by how they obtain energy and carbon
–
–
–
–
Phototrophs obtain energy from light
Chemotrophs obtain energy from chemicals
Autotrophs require CO2 as a carbon source
Heterotrophs require an organic nutrient to make organic compounds
• Energy and carbon sources are combined to give four major modes
of nutrition
The Role of Oxygen in Metabolism
• Prokaryotic metabolism varies with respect to O2
– Obligate aerobes require O2 for cellular
respiration
– Obligate anaerobes are poisoned by O2 and use
fermentation or anaerobic respiration
– Facultative anaerobes can survive with or
without O2
Nitrogen Metabolism
• Nitrogen is essential for the production
of amino acids and nucleic acids –
nitrogen fixation
– some prokaryotes convert atmospheric
nitrogen (N2) to ammonia (NH3)
– Some cooperate between cells of a colony
• allows them to use environmental resources
they could not use as individual cells
– E.g. cyanobacterium Anabaena, photosynthetic
cells and nitrogen-fixing cells called heterocysts
(or heterocytes) exchange metabolic products
Photosynthetic
cells
Heterocyst
20 m
Molecular systematics led to the splitting of
prokaryotes into bacteria and archaea
Eukaryotes
Euryarchaeotes
Crenarchaeotes
UNIVERSAL
ANCESTOR
Nanoarchaeotes
Domain Archaea
Korarchaeotes
Proteobacteria
Spirochetes
Cyanobacteria
Gram-positive
Domain Bacteria
Chlamydias
Clades of Domain Bacteria
• Fig 27.18
(27.13 in 7th ed.)
• Proteobacteria
– diverse & includes gram-negatives
– Subgroups: α, β, γ, δ, ε
•
•
•
•
Chlamydias
Spirochaetes
Cyanobacteria
Gram positive bacteria
Proteobacteria
• Alpha subgroup
• Rhizobium
– Nitrogen-fixing
bacteria reside in
nodules of legume
plant roots
– Convert atmospheric
N2 to usable inorganic
form for making
organics (i.e. amino
acids)
Proteobacteria
Gamma subgroup
• Includes many Gram
negative bacteria
– E. coli
• common intestinal flora
– Enterobacter aerogenes
• Pathogenic; causes UTI
– Serratia
• Facultative anaerobe
• Characteristically red
cultures
Proteobacteria: Myxobacteria
• Delta subgroup of
Proteobacteria
– Slime-secreting
decomposers
– Elaborate colonies
• Thrive collectively, yet
have the capacity to
live individually at some
point in their life cycle
– Release myxospores
from “fruiting” bodies
Chlamydias
Chlamydias
2.5 m
• parasites that live
within animal cells
• Chlamydia trachomatis
causes blindness and
nongonococcal
urethritis by sexual
transmission
Chlamydia (arrows) inside an
animal cell (colorized TEM)
Spirochaetes
• Long spiral or helical
heterotrophs
– Flagellated cell wall
• Decomposers &
pathogens
• Some are parasites,
including Treponema
pallidum, which causes
syphilis, and Borrelia
burgdorferi, which
causes Lyme disease
Cyanobacteria
• “blue-green algae”
• Photoautotrophic
– Generate O2 as a
significant primary
producer in aquatic
systems
• Typically colonial
– Filamentous
• Plant chloroplasts likely
evolved from
cyanobacteria by the
process of endosymbiosis
Oscillatoria (Cyanobacteria) 1
Oscillatoria 2
Anabaena (Cyanobacteria) 1
• Vegetative cell
– Primary metabolic function
(photosynthesis)
• Heterocyst
– Nitrogen fixation
• Akinete
– Dormant spore forming cell
Anabaena 2
Anaebena 3
Nostoc (Cyanobacteria) 1
Nostoc 2
Gleocapsa (Cyanobacteria) 1
Gleocapsa 2
Gram positive bacteria
• Gram stains – purple
– Thick cell wall
• Includes:
– Micrococcus
• Common soil bacterium
• M. luteus cultures have a yellow
pigment
– Some Staphylococcus and
Streptococcus, can be
pathogenic
– Bacillus
• B. subtilis are relatively large rods;
common “lab organism”
• Bacillus anthracis, the cause of
anthrax
– Actinomycetes, which
decompose soil
– Clostridium botulinum, the
cause of botulism
– Mycoplasms, the smallest
known cells
Hundreds of mycoplasmas covering a human fibroblast cell
(colorized SEM)
Domain Archaea
Archaea -- “Extremophiles”
Many are tolerant to extreme
environments
– Extreme thermophiles
• High and low temperature
• Commonly acidophilic
• E.g. hot sulfer springs, deep
sea vents
– Extreme halophiles
• High salt concentration
• Often contains carotenoids
• E.g. Salton Sea
– Methanogens
• Anaerobic environments
– Release methane
– E.g. animal guts