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