[asa] Building a flagellum step by step

Biological complexity reduced:

Open access to the full article at
http://www.pnas.org/cgi/reprint/104/17/7116

Stepwise formation of the bacterial flagellar system
Renyi Liu* and Howard Ochman*†‡

Elucidating the origins of complex biological structures has been
one of the major challenges of evolutionary studies. The bacterial
flagellum is a primary example of a complex apparatus whose
origins and evolutionary history have proven difficult to reconstruct.
The gene clusters encoding the components of the flagellum
can include >50 genes, but these clusters vary greatly in their
numbers and contents among bacterial phyla. To investigate how
this diversity arose, we identified all homologs of all flagellar
proteins encoded in the complete genome sequences of 41 flagellated
species from 11 bacterial phyla. Based on the phylogenetic
occurrence and histories of each of these proteins, we could
distinguish an ancient core set of 24 structural genes that were
present in the common ancestor to all Bacteria. Within a genome,
many of these core genes show sequence similarity only to other
flagellar core genes, indicating that they were derived from one
another, and the relationships among these genes suggest the
probable order in which the structural components of the bacterial
flagellum arose. These results show that core components of the
bacterial flagellum originated through the successive duplication
and modification of a few, or perhaps even a single, precursor
gene.

-- 
Dr. David Campbell
425 Scientific Collections
University of Alabama
"I think of my happy condition, surrounded by acres of clams"
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