1. The bacterial world

2. Bacteria in the living world
Bacteria = one of the three groups of organisms on Earth
The first bacteria appeared on Earth 3,8 billion years ago !!
« Only » 7300 species known at this time
(but it’s estimated that there are several million undiscovered…)

3. What are bacteria ?
Bacteria = also named prokaryotes, compared to eukaryotes cells
Prokaryotes (bacteria) Eukaryotes (for example animal cell or vegetal cell)

4. Comparison of characteristics
What are bacteria ?
Comparison of characteristics
Bacteria
Eukaryotes
Always unicellular
Unicellular or multicellular
1 to 5 μm on average
10 to 100 μm on average
No organits
Many differents organits (Golgi, reticulum…)
Free nuclear DNA in cell (no envelope to delimit)
Organized nucleus with DNA enclosed in an envelope
Not a real nucleus
 Pro ( = nearly in Greek) karyo (= nucleus in Greek)
Real nucleus
 Eu ( = true in Greek) karyo (= nucleus in Greek)

5. Different groups of bacteria
Two main groups depending on the form of bacteria
Rods
Cocci
Examples :
Staphylococcus, Streptococcus, Lactococcus…
Examples :
Salmonella, E.coli, Pseudomonas…

6. Bacteria structure
Example with a rod :

7. Bacteria structure
Their structural characteristics confer special properties :
Thick cell wall and capsule
 resistance in environment and against immune system of humans and animals…
Dynamic genetic material
 rapid acquisition of new properties (antibiotics resistance, toxin production…)
Flagellum
 mobility
Pili
 adhesiveness on different
materials or living tissue

8. Bacterial ecology Where live bacteria ??? … EVERYWHERE ON EARTH !!
Independently in the environment :
- aquatic (pond, river, sea…)
- soil
- air (only a way of conveyance)
… sometimes in extreme environments (volcano, geyser, deep trenches…)
In contact with other living organisms :
- humans
- animals
- plants…
Example : Thermotoga maritima, bacteria that lives at 90°C in volvanic hot springs

9. Bacterial ecology
The differents relationship bacteria with humans, animals, plants…
Symbiosis
 Bacteria do not cause problems and are benefit to the host
Pathogenic
 Bacteria cause troubles and diseases to their host
Commensalism
 Bacteria live on the host without causing troubles
Only some dozen of species (a few part of the 7300 species known) !!!! But control of these bacteria is important :
-in medical context
-in consumer products (pharmaceuticals, food…)