Bacteria and Archea : The Prokaryotes
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Transcript of Bacteria and Archea : The Prokaryotes
Bacteria and Archea:Bacteria and Archea:The ProkaryotesThe Prokaryotes
Archae & Bacteria
There are almost everywhere !!!
They are the most numerous organisms
that can be found in all habitats
Prokaryotes
• 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
• Cells have a diversity of shapes the most common being
– spheres (cocci)– rods (bacilli)– helices (spirilla and spirochetes).
• 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
UNIVERSALANCESTOR
Eukaryotes
Korarcheotes
Euryarchaeotes
Crenarchaeotes
Nanoarchaeotes
Proteobacteria
Chlamydias
Spirochetes
Cyanobacteria
Gram-positivebacteria
Dom
ainE
ukarya
Dom
ain A
rchaeaD
omain
Bacteria
Prokaryote Cell walls:
• Cell walls:– Maintain the cell shape.– Protect the cell.– Prevent the cell from bursting in a
hypotonic environment.
• Eubacteria walls contain peptidoglycan
– archae cell walls lack peptidoglycan– Peptidoglycan = Modified sugar
polymers cross-linked by short polypeptides.
Gram Staining
• 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.
• Have more complex cell walls with less peptidoglycan.
• An outer lipopolysaccharide-containing membrane blocking the stain from the peptidoglycan.
– Stain pink, with safranin
• More likely to be disease causing
Fig 7.4 Prokaryote cell structure
• 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 protein2.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.
• 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
• Some prokaryotes have specialized regions of internal membranes
– formed by invaginations of the plasma membranes.
Fig 27.8 Specialized membranes
Prokaryotic Genomes
• Genophore = usually one double-stranded, 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
• 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
F+ cell
F– cell
Matingbridge
Bacterial chromosome
Bacterialchromosome
(a) Conjugation and transfer of an F plasmid
F+ cell
F+ cell
F– cell
(b) Conjugation and transfer of part of an Hfr bacterial chromosome
F factor
Hfr cell A+A+
A+
A+
A+A– A– A–
A– A+
RecombinantF– bacterium
Examples of Conjugation
Why is antibiotic resistance increasing ?
Gene Expression
• Prokaryotic and eukaryotic DNA replication and translation are similar
– Same genetic code
• Bacterial ribosomes smaller and have different protein and RNA content
Cell Growth
• They divide by Binary Fission.– Genophore attached to plasma
membrane– Copies as membrane elongates– New wall forms in between
• 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
• Energy source (make ATP) – from light (phototrophs),– use chemicals in the environment
(chemotrophs).
• Carbon source – autotrophs utilize CO2 directly
– heterotrophs require at least one organic nutrient as a carbon source.
Major Modes of Nutrition:
• Photoautotrophs• Chemoautotrophs• Photoheterotrophs• Chemoheterotrophs
Table 27-1
Nutritional Diversity Among Chemoheterotrophs
• 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
• Nitrogen fixing bacteria (N2 ->NH3)– In soil, and some plant root nodules
• Nitrifying bacteria convert NH3 -> NO2 – In soil, or biotower in treatment plant
• 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
.
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)
• 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)
• Methanogens. – Use H2 to reduce C02 to CH4 and
are strict anaerobes– In Digester at treatment plant
• Extreme Halophiles – inhabit high salinity ( 15-20%)
environments (e.g. Dead Sea).
• Extreme Thermophiles – Live in habitats of 60 - 80C.
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
• 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
Cause disease by
Non-Life Bio-particles
• Virus: need a living cell to reproduce
• Viroids: naked RNA
• Prions: rogue free proteins
Viral cycleFig 18.3
Herpes
Prions Fig. 18.10