The bacterial world Bacteria in the living 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…)