Towards multicellularity Colonial organizati on Informatio n exchange Apoptosis External secretion Four elements to make a multicelluar organism Paenibacillus dendritiformis Bacteria Paenibacillus •forms colonies •moves on hard surfaces through jointly secreted lubricants •communicates with other cells •no apoptosis •no real cell differentiation Myxococcus xanthus Myxobacteria •form colonies of millions of cells •Some have coordinated movements •form biofilms •largest bacterial genomes (9 - 12 kB) •some produce fruiting bodies for the release of spores •no apoptosis •rudimentary cell differentiation Why did Bacteria not evolve true multicellularity? Maybe their limits in genome size do not allow for higher order differentiation.
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Towards multicellularity Colonial organization Information exchange Apoptosis External secretion Four elements to make a multicelluar organism Paenibacillus.
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Towards multicellularity
Colonial organization
Information exchange
ApoptosisExternal secretion
Four elements to make a multicelluar organism
Paenibacillus dendritiformis
Bacteria
Paenibacillus•forms colonies•moves on hard surfaces through jointly secreted lubricants•communicates with other cells•no apoptosis•no real cell differentiation
Myxococcus xanthus
Myxobacteria•form colonies of millions of cells•Some have coordinated movements•form biofilms•largest bacterial genomes (9 - 12 kB)•some produce fruiting bodies for the release of spores•no apoptosis•rudimentary cell differentiation
Why did Bacteria not evolve true multicellularity?
Maybe their limits in genome size do not allow for higher order differentiation.
During the Cambrian atmospheric oxygen concentration increased to a level to allow for the development of hard skeletons. Probably all today’s phyla were already present.
First complicated food webs including higher predators appeared. This might have caused the disappearance of the Ediacaran fauna.
http://www.palaeos.com/Paleozoic/Cambrian/Cambrian.htmThe history of life: http://www.palaeos.com/The tree of life: http://www.tolweb.org/tree/The virtual fossil museum: http://www.fossilmuseum.net/
On the cambrian explosion: http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1578734
Metazoan phylogeny: the state of art.:http://icb.oxfordjournals.org/cgi/content/full/46/2/93
Dunn C. W. et al. (2008) Broad phylogenomic sampling improves resolution of the animal tree of life. Nature 452: 745-750. Srivastava M. et a. 2008. The Trichoplax genome and the nature of placozoans. Nature 453: 855-960..