Nick Matzke’s problematic evolutionary narrative of the Type Three Secretory System (TTSS) into the bacterial flagellum quickly made it into a peer reviewed journal while the response from the ID camp took two years longer. Our position, which I mentioned several times in the past, was that the flagellum preceded the TTSS in nature and thus the TTSS represents a devolution from flagella rather than flagella being evolved from a TTSS. Nick had it ass-backward. No surprise there. Devolution is much easier than evolution, Nick. Always look for devolutionary explanations first. I’d like to say that devolution being far easier than evolution is something that ID predicts but alas, it’s predicted by nothing more than common sense. Of course ID is predicated by common sense too so there is that kinship to consider.
Molecular Biology and Evolution 2008 25(9):2069-2076
The evolution of the flagellar assembly pathway in endosymbiotic bacterial genomes
Toft C and Fares MA
Department of Genetics, Smurfit Institute of Genetics, University of
Dublin, Trinity College, Dublin 2, Ireland.
Genome shrinkage is a common feature of most intra-cellular pathogens
and symbionts. Reduction of genome sizes is among the best-characterised
natural strategies adopted by intra-cellular organisms to save and avoid
maintaining expensive redundant biological processes. Endosymbiotic
bacteria of insects are examples of biological economy taken to
completion because their genomes are dramatically reduced. These
bacteria are non-motile and their biochemical processes are intimately
related to those of their host. Because of this relationship, many of
the processes in these bacteria have been either lost or have suffered
massive re-modelling to adapt to the intra-cellular symbiotic lifestyle.
An example of such changes is the flagellum structure that is essential
for bacterial motility and infectivity. Our analysis indicates that
genes responsible for flagellar assembly have been partially or totally
lost in most intra-cellular symbionts of gamma-Proteobacteria.
Comparative genomic analyses show that flagellar genes have been
differentially lost in endosymbiotic bacteria of insects. Only proteins
involved in protein export within the flagella assembly pathway (type
III secretion system and the basal-body) have been kept in most of the
endosymbionts whereas those involved in building the filament and hook
of flagella have only in few instances been kept, indicating a change in
the functional purpose of this pathway. In some endosymbionts, genes
controlling protein-export switch and hook length have undergone
functional divergence as shown through an analysis of their evolutionary
dynamics. Based on our results we suggest that genes of flagellum have
diverged functionally as to specialise in the export of proteins from
the bacterium to the host.