Download The bacterial world

The bacterial world
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…)
What are bacteria ?
Bacteria = also named prokaryotes,
compared to eukaryotes cells
Prokaryotes (bacteria)
Eukaryotes (for example
animal cell or vegetal cell)
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)
Different groups of bacteria
Two main groups depending on the
form of bacteria
Cocci
Examples :
Staphylococcus,
Streptococcus, Lactococcus…
Rods
Examples :
Salmonella, E.coli,
Pseudomonas…
Bacteria structure
Example with a rod :
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
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…)
Example : Thermotoga
maritima, bacteria that
lives at 90°C in
volvanic hot springs
In contact with other
living organisms :
- humans
- animals
- plants…
Bacterial ecology
The differents relationship bacteria with
humans, animals, plants…
Symbiosis
 Bacteria do not
cause problems and are
benefit to the host
Commensalism
 Bacteria live on the
host without causing
troubles
Pathogenic
 Bacteria cause
troubles and diseases
to their host
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…)