Bacteria and Archaea

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many antibiotics (colorized SEM)

5 µm

1 µm

Hundreds of mycoplasmas

covering a human fibroblast

cell (colorized SEM)

Slide 41

Cyanobacteria

Cyanobacteria are photoautotrophs that generate O2

Plant chloroplasts likely evolved from cyanobacteria by endosymbiosis.

Slide 42

Cyanobacteria: One of the Major Groups of Bacteria

50 µm

Two species of Oscillatoria,

filamentous cyanobacteria (LM)

Slide 43

Gram-Positive Bacteria

Gram-positive bacteria include

Actinomycetes, which decompose soil.

Bacillus anthracis, the cause of anthrax.

Clostridium botulinum, the cause of botulism.

Some Staphylococcus and Streptococcus, which can be pathogenic.

Mycoplasms, the smallest known cells.

Slide 44

Prokaryotes play crucial roles in the biosphere. Chemical Cycling

Prokaryotes play a major role in the recycling of chemical elements between the living and nonliving components of ecosystems.

Chemoheterotrophic prokaryotes function as decomposers (saphrophytes) breaking down corpses, dead vegetation, and waste products.

Nitrogen-fixing prokaryotes add usable nitrogen to the environment.

Prokaryotes can increase the availability of nitrogen, phosphorus, and potassium for plant growth.

Prokaryotes can also “immobilize” or decrease the availability of nutrients.

Slide 45

Ecological Interactions

Symbiosis is an ecological relationship in which two different species live in close contact: a larger host and smaller symbiont.

In mutualism, + + both symbiotic organisms benefit.

In commensalism, + 0 one organism benefits while neither harming nor helping the other.

In parasitism, + - an organism called a parasite harms but does not kill its host. Parasites that cause disease are called pathogens.

Slide 46

Pathogens: Bacteria Causing Lyme Disease are transmitted by deer ticks

5 µm

Slide 47

Pathogenic prokaryotes typically cause disease by releasing exotoxins or endotoxins.

Exotoxins cause disease even if the prokaryotes that produce them are not present.

Endotoxins are released only when bacteria die and their cell walls break down.

Many pathogenic bacteria are potential weapons of bioterrorism.

Slide 48

Prokaryotes in Research and Technology