Ch. 27: Bacteria and Archaea

Modern/regular/eubacteria and the ancient methanogens Prokaryote cells with cell membranes,

cytoplasm/cytosol, DNA in the form of one circular chromosome and many plasmids, and 70s ribosomes.

Shapes are cocci, bacilli, spirillum May have cell wall, flagella, cilia and

other structures

Adaptations

Adaptations to extremes of climate from freezing to boiling to acidic and salty. (species specific ranges) Salt tolerant up to 32% Hot springs - thermophiles Near frozen waters at arctic Acid conditions; 0.03 pH !! – acidophiles 3 million Rads of radiation

Fig. 27-1

Structure and functions contribute to success Unicellular but may aggregate into colonies Cell walls; Gram positive and gram negative

based on peptidoglycans and lipids Capsules; waxy layer that helps avoid

antibiotics Fimbriae (like velcro) and pili (trade plasmids) Motility; cilia and flagella and taxis; roughly 50%

are capable of movement – at relatively fast speeds

Plasmids

Fig. 27-3

Cellwall

Peptidoglycanlayer

Plasma membrane

Protein

Gram-positivebacteria

(a) Gram-positive: peptidoglycan traps crystal violet.

Gram-negativebacteria

(b) Gram-negative: crystal violet is easily rinsed away, revealing red dye.

20 µm

Cellwall

Plasma membrane

Protein

Carbohydrate portionof lipopolysaccharide

Outermembrane

Peptidoglycanlayer

Internal and Genomic Organization

Not usually any internal, membrane-bound structures

May have specialization built into PLASMA MEMBRANE

70s ribosomes; smaller than eukaryotic, solid (erythromycin and tetracycline)

Nucleoid region One, circular chromosome, hundreds of genes, fills

central portion, Many plasmids – copies of frequently or currently

used genes

Adaptations of reproduction

Binary fission – one cell divides into 2 those into 4 those into 8, etc.

Can occur every hour at optimal conditions, some species every 20 minutes, typical is 24 hours

1 bacteria could create a colony outweighing Earth in 3 days…. Obvious checks and balances here. Nutrient supply Toxins/ poison selves Competition Space - pressure

Bacterial Populations1. They are very small organisms

0.5 – 5 m ( eukaryotic are 10-100 m)2. They reproduce by binary fission3. They have very short generation times4. ENDOSPORES can survive harsh

conditions and survive for centuries5. MSU study looked at 20,000

generations in 8 years – evidence of evolution

6. Simpler – but not inferior or primative7. On Earth for over 3.5 billion years now

Diversity Three events lead to diversity

Rapid reproduction Most variety in sexually reproducing species is

from arrangement/ shuffling of alleles during meiosis

Insertions, deletions, base pair substitutions Mutations still very RARE, but sheer numbers of

organisms and time per generation means more are expressed

Mutation More variety in ribosomal RNA between 2 strains

of E.coli than between human and platypus Genetic recombination

Next page

Genetic Recombination

Transformation Bacteria are able to absorb genetic

information from their surroundings Transduction

Bacterial genes are also spread between bacteria populations by viruses known as bacteriophages

Conjugation Pili bridge bacteria and they trade plasmids F factor and R factor

Fig. 27-11-4

Recombinant cell

Recipientcell

A+ B–

B–

A+

A–

Recombination

A+

Donorcell

A+ B+

A+ B+

Phage DNA

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

Metabolic adaptations (table 27.1)

Metabolism Oxygen Metabolism

Obligate aerobes Obligate anaerobes Facultative anaerobes

Nitrogen Metabolism N is essential for amino acids Atmospheric N isn’t highly useable Microbes ‘fix’ nitrogen into nitrate, nitrites and

ammonium ions that are useable Metabolic Cooperation

Colonies of cells that fix nitrogen and produce oxygen so that neighboring area is hospitable

Ocean floor and dental plaque

Molecular Systematics Previously bacterial classification (systematics)

used motility, shape, nutrition and gram staining Molecular systematics has drastically changed

the classification – Much more diverse than assumed 6000+ species/strains ID and named A soil sample could contain over 10,000 species Horizontal transfers of genes blur “root” for this

region of the tree of life Two main branches are Archaea and Bacteria

Groups of Bacteria

Eukarya

Archaea

Bacteria

Fig. 27-18a

Alpha

Beta

Gamma

Delta

Epsilon

Proteobacteria

Subgroup: Beta Proteobacteria

Nitrosomonas (colorized TEM)

1 µ

m

Subgroup: Delta Proteobacteria

10 µ

m

Fruiting bodies ofChondromyces crocatus, amyxobacterium (SEM)

Bdellovibrio bacteriophorusattacking a larger bacterium(colorized TEM)

5 µ

m

Helicobacter pylori (colorized TEM)

2 µ

m0.

5 µ

m

Subgroup: Epsilon Proteobacteria

B. bacteriophorus

Thiomargarita namibiensiscontaining sulfur wastes (LM)

Subgroup: Gamma Proteobacteria

Subgroup: Alpha Proteobacteria

Rhizobium (arrows) inside aroot cell of a legume (TEM)

2.5

µm

Fig. 27-18i

CHLAMYDIAS

2.5

µm

CYANOBACTERIA

SPIROCHETES

GRAM-POSITIVE BACTERIA

Chlamydia (arrows) inside ananimal cell (colorized TEM)

Leptospira, a spirochete(colorized TEM)

5 µ

m

50

µm

Two species of Oscillatoria,filamentous cyanobacteria (LM)

Streptomyces, the source ofmany antibiotics (colorized SEM)

5 µ

m

1 µ

m

Hundreds of mycoplasmascovering a human fibroblastcell (colorized SEM)

Positive Roles of Bacteria Decomposers Symbioses

Mutualism Commensalism – normal flora (parasitism – not positive)

Chemical recycling Nitrogen Oxygen Carbon

Research and Technology Food (cheese) and beverages Waste water treatment Genetic engineering

Negative Impacts of Bacteria Parasitic bacteria that cause disease are

called PATHOGENS Opportunistic Exotoxins and endotoxins