Post on 29-Dec-2015
The bacterial world
Bacteria in the living Bacteria in the living worldworld
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 ?What are bacteria ?
Bacteria = also named prokaryotes, compared to eukaryotes cells
Prokaryotes (bacteria) Eukaryotes (for example animal cell or vegetal cell)
What are bacteria ?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 Different groups of bacteriabacteriaTwo main groups depending on the form of bacteria
Cocci Rods
Examples :Staphylococcus, Streptococcus, Lactococcus…
Examples :Salmonella, E.coli, Pseudomonas…
Bacteria structureBacteria structureExample with a rod :
Bacteria structureBacteria structureTheir structural characteristics confer special properties :
Thick cell wall and capsule resistance in environment and against
immune system of humans and animals…
Flagellum mobility
Pili adhesiveness on differentmaterials or living tissue
Dynamic genetic material rapid acquisition of new properties (antibiotics resistance, toxin production…)
Bacterial ecologyBacterial ecologyWhere 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 ecologyBacterial ecologyThe 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…)