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…)