Transcript Prokaryotes and the origins of Metabolic Diversity

Bacteria and Archea:
The Prokaryotes
Archae & Bacteria
There are almost everywhere
!!!
They are the most numerous
organisms that can be
found in all habitats
Prokaryotes
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Appear approximately 3.5 BYA
Were the earliest living organisms
Have specialized into all habitats
Have all types of metabolism
– Origin of aerobic and other types of
respiration
– Origin of several types of photosynthesis
Prokaryotes: Tremendous impact on
the Earth
• Very few cause diseases
• As fixers and decomposers they are
essential in geo-chemical cycles
• Many form symbiotic relationships with
other prokaryotes and eukaryotes
• Mitochondria and chloroplasts may be
descended from symbiotic bacteria
Prokaryotes as compared to eukaryotes:
• Typically smaller in size
• Lack membrane bound
organelles
• Most have cell walls – but
different chemical composition
• Have simpler genomes
Morphological Diversity of Prokaryotes
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Cells have a diversity of shapes the
most common being
– spheres (cocci)
– rods (bacilli)
– helices (spirilla and spirochetes).
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Prokaryotes are generally single-celled
– some aggregate into two-celled to several
celled groups
– Some have specialized functions,
heterocysts in Anabaena.
• Fig 27.3
Fig. 27-16
Euryarchaeotes
Crenarchaeotes
UNIVERSAL
ANCESTOR
Domain Archaea
Korarcheotes
Domain
Eukarya
Eukaryotes
Nanoarchaeotes
Proteobacteria
Spirochetes
Cyanobacteria
Gram-positive
bacteria
Domain Bacteria
Chlamydias
Prokaryote Cell walls:
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Cell walls:
– Maintain the cell shape.
– Protect the cell.
– Prevent the cell from bursting in a
hypotonic environment.
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Eubacteria walls contain peptidoglycan
– archae cell walls lack peptidoglycan
– Peptidoglycan = Modified sugar polymers
cross-linked by short polypeptides.
Gram Staining
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Gram stain is used to distinguish two
groups of eubacteria by structural
differences in their cell walls.
Gram-positive eubacteria.
– Cell walls with large amounts of
peptidoglycan that react with Crystal
Violet stain
Gram-negative eubacteria.
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Have more complex cell walls with less
peptidoglycan.
An outer lipopolysaccharide-containing
membrane blocking the stain from the
peptidoglycan.
– Stain pink, with safranin
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More likely to be disease causing
Fig 7.4 Prokaryote cell structure
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Capsule= a gelatinous secretion which
provides cells with additional protection
Pili = Surface appendages used for
adherence to a host (in the case of a
pathogen), or for transferring DNA in
conjugate.
Fig 27.6 Pili
The Motility of Prokaryotes: three
mechanisms :
1. Swimming with Flagella: differ from
eukaryotic:
1. Solid protein
2. Rotate like an oar, rather than whip back
and forth
3. The basal apparatus rotation is powered by
the diffusion of protons into the cell.
Flagella
Fig 27.7
2. Filaments
– axial filaments are attached to basal
motors at either end of the cell.
– rotate the cell like a corkscrew.
– more effective in viscous substrates than
flagella.
3. Gliding
– Some bacteria move by gliding through a
layer of slimy chemicals secreted by the
organism.
Taxis= Directed Movement towards or away
from a stimulus.
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light (phototaxis)
chemical (chemotaxis)
magnetic field (magnetotaxis)
Positive taxis movement toward a
stimulus.
• Movement away from a stimulus is a
negative taxis
Non directional
Directional
Chemotaxis Test
Internal Membranous Organization
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Some prokaryotes have specialized
regions of internal membranes
– formed by invaginations of the plasma
membranes.
Fig 27.8 Specialized membranes
Prokaryotic Genomes
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Genophore = usually one doublestranded, circular DNA molecule
– attached to cell membrane.
Plasmid
• Smaller independent rings of DNA
– “extra genes” -antibiotic resistance or
metabolism of unusual nutrients.
– Replicate independently of the genophore.
– Can be transferred between partners
during conjugation
– Also found in yeasts, (fungi - eukaryotes)
Amount of DNA
Genetic Recombination
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Transformation = external DNA is
incorporated by bacterial cells.
Conjugation = transfer of genes from
one bacterium to another.
Transduction = transfer of genes
between bacteria via viruses.
Conjugation
Fig. 27-13
F plasmid
Bacterial chromosome
F+ cell
F+ cell
Mating
bridge
F– cell
F+ cell
Bacterial
chromosome
(a) Conjugation and transfer of an F plasmid
Hfr cell
A+
A+
F factor
F– cell
A+
A+
A–
Recombinant
F– bacterium
A–
A–
(b) Conjugation and transfer of part of an Hfr bacterial chromosome
A+
A–
A+
Examples of Conjugation
Why is antibiotic resistance increasing ?
Gene Expression
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Prokaryotic and eukaryotic DNA
replication and translation are similar
– Same genetic code
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Bacterial ribosomes smaller and have
different protein and RNA content
Cell Growth
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They divide by Binary Fission.
– Genophore attached to plasma
membrane
– Copies as membrane elongates
– New wall forms in between
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Mitochondria, chloroplasts divide by
binary fission too
No Mitosis, nor Meiosis.
All haploid
Binary
Fission
Fig. 12.10
• Endospore =
Resistant cells
– Genophore
surrounded by
a thick wall.
Anthrax sp. endospore
Major Modes of Nutrition
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Energy source (make ATP)
– from light (phototrophs),
– use chemicals in the environment
(chemotrophs).
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Carbon source
– autotrophs utilize CO2 directly
– heterotrophs require at least one organic
nutrient as a carbon source.
Major Modes of Nutrition:
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Photoautotrophs
Chemoautotrophs
Photoheterotrophs
Chemoheterotrophs
Table 27-1
Nutritional Diversity Among
Chemoheterotrophs
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Saprobes are decomposers that
absorb nutrients from dead organic
matter.
Parasites are cells that absorb
nutrients from body fluids of living
hosts
compounds that cannot be used as a
carbon source by bacteria/fungi are
termed non-biodegradable
Nitrogen Metabolism
In amino acids, nucleotides
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Nitrogen fixing bacteria (N2 ->NH3)
– In soil, and some plant root nodules
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Nitrifying bacteria convert NH3 -> NO2
– In soil, or biotower in treatment plant
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Denitrifying bacteria N02 -(Nitrite) or
N03 (Nitrate) to atmospheric N2
– In soil, counter-act fertilizers
The nitrogen fixing Cyanobacteria are very self-sufficient, they need only
light energy, C02, N2, water and a few minerals to grow
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Oxygen metabolism
• Obligate aerobes
• Facultative anaerobes
• Obligate anaerobes
Three Domains Fig 27.2
Domain Bacteria (Eubacteria)
• a very diverse assemblage of
organisms.
• forms which exhibit every known mode
of nutrition and energy metabolism.
Domain Archaea (Archaebacteria)
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Cell walls lack peptidoglycan.
Plasma membranes have a unique
lipid composition.
RNA polymerase and ribosomal
protein are more like those of
eukaryotes than of eubacteria
Common ancestor with Eukaryotes after
split from Bacteria.
Domain Archaea (Archaebacteria)
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Methanogens.
– Use H2 to reduce C02 to CH4 and are
strict anaerobes
– In Digester at treatment plant
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Extreme Halophiles
– inhabit high salinity ( 15-20%)
environments (e.g. Dead Sea).
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Extreme Thermophiles
– Live in habitats of 60 - 80C.
Hot springs
Salt ponds
Bacteria and Disease:
• Pathogenic= invade, attack host
• Opportunistic = Normal inhabitants of
the body that become pathogenic
• Defense: greatly reduced mortality due
to bacterial diseases
Cause disease by
• Growth and invasion of tissues
• Production of a toxin
– Exotoxin =Proteins secreted by bacterial
cells.
– Endotoxin = Toxic component of outer
membranes of some gram-negative
bacteria
Non-Life Bio-particles
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Virus: need a living cell to reproduce
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Viroids: naked RNA
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Prions: rogue free proteins
Viral cycle
Fig 18.3
Herpes
Prions Fig. 18.10