Parasitology

Research Article

Bacterial symbiont and salivary peptide evolution in the context of leech phylogeny

MARK E. SIDDALLa1 c1, GI-SIK MINa2, FRANK M. FONTANELLAa3, ANNA J. PHILLIPSa1a4 and SARA C. WATSONa1

a1 Sackler Institute of Comparative Genomics & Division of Invertebrate Zoology, American Museum of Natural History, New York, NY, USA

a2 Department of Biological Sciences, Inha University, Yonghyun-dong, Nam-Gu, Incheon 402-751, Korea

a3 Department of Biology, Brigham Young University, Provo, UT 84602, USA

a4 Department of Biology, The Graduate Center, The City University of New York, New York, NY, USA

SUMMARY

The evolutionary history of leeches is employed as a general framework for understanding more than merely the systematics of this charismatic group of annelid worms, and serves as a basis for understanding blood-feeding related correlates ranging from the specifics of gut-associated bacterial symbionts to salivary anticoagulant peptides. A variety of medicinal leech families were examined for intraluminal crop bacterial symbionts. Species of Aeromonas and Bacteroidetes were characterized with DNA gyrase B and 16S rDNA. Bacteroidetes isolates were found to be much more phylogenetically diverse and suggested stronger evidence of phylogenetic correlation than the gammaproteobacteria. Patterns that look like co-speciation with limited taxon sampling do not in the full context of phylogeny. Bioactive compounds that are expressed as gene products, like those in leech salivary glands, have ‘passed the test’ of evolutionary selection. We produced and bioinformatically mined salivary gland EST libraries across medicinal leech lineages to experimentally and statistically evaluate whether evolutionary selection on peptides can identify structure-function activities of known therapeutically relevant bioactive compounds like antithrombin, hirudin and antistasin. The combined information content of a well corroborated leech phylogeny and broad taxonomic coverage of expressed proteins leads to a rich understanding of evolution and function in leech history.

(Received February 2011)

(Revised March 07 2011)

(Accepted March 08 2011)

(Online publication May 10 2011)

Correspondence:

c1 Corresponding author: Mark E Siddall. E-mail: siddall@amnh.org

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