Peter’s Notes and Links on Giardia

Pictures at MBL microscope

How to build trees:  Parsimony, ml, distance (see here)

Logdet: distances that work well when the composition of sequences varies, but the measure is very sensitive to among site rate variation. 

Long Branch Attraction (LBA) tendency to long branches to group together in phylogenetic reconstructions.  (See Olga’s online poster)

Giardia:  ATPase subunit phylogenies (as well as most other protein families) have Giardia as deepest eukaryotic branch (however Giardia shares only 5 signature residues with the outgroup, (Trichomonas share 25) (Microsporidia go with the fungi));  however, the V-ATPase is a typical eukaryotic V-ATPase.  There are no indications whatsoever that this ATPase might function in ATP synthesis (similar to the archaeal type ATP synthases (here).

Also:

•    While Giardia normally does not have a visible Golgi apparatus (nor do fast growing yeast cells), it was suggested to be present during encystation (here recent review here), and many Golgi typical enzymes were discovered in the Giardia genome (e.g. here and here)
•    Giardia has spliceosomal introns (here)
•    Giardia contains mitosomes, which apparently have evolved from mitochondria (or the endosymbiont that gave rise to the mitochondria. (here)

Bottomline:  Giardia and other diplomonads, while possibly representing a deep branching eukaryotic lineage, do not appear to be a missing link between the prokaryotic and the eukaryotic cell organization.