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

Abstract

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.

Metagenomic analysis of the medicinal leech gut microbiota

“…Prior studies of the leech gut microbiome relied on culturing or Sanger sequencing of clone libraries (Graf, 1999; Worthen et al, 2006; Siddall et al, 2007, 2011; Laufer et al, 2008). In this study, we utilized V6 region pyrosequencing of the 16S rRNA gene to characterize the two compartments of the leech digestive tract, the crop and intestinum, to determine the presence of less abundant organisms (Figure 1).…”

Bacterial symbioses of the medicinal leech Hirudo verbana

“…However, it is possible that each species produces a different complement of secreted proteins, and greater attention should be given to correctly identify the species of leech used in medical procedures. 26,30,31 Although standard practice dictates the administration of certain antibiotics prior to treatment, in ~5-15% of leech therapy cases for venous congestion treatment is followed by a bacterial infection of the bite wound, with higher rates of infection (~25-35%) occurring in patients that were not treated with antibiotics prophylactically. 26,31,32 Culture-based recovery and biochemical identification of wound isolates indicated that Aeromonas species were typically the cause of these infections.…”

“…45 Of note, recent work by Siddall et al has interestingly shown that the phylogenetic distribution of Aeromonas sp recovered from different species of leeches caught in the wild does not accurately reflect the established phylogeny of the leeches themselves. 30 This apparent lack of co-evolution is intriguing, however only a few specimens have so far been analyzed, and these studies utilized sequenced PCR products, which often detect only the most abundant organisms. Considering that the taxonomy of the Aeromonads is still very much in the process of being refined, and that commercial phenotypic tests used in clinical settings often miss-identify some Aeromonas species as A. hydrophila, there is a concern that isolates previously identified as A. hydrophila from wound infections following leech therapy could be actually be A. veronii.…”

Genetic variation and species identification among selected leeches (Hirudinea) revealed by RAPD markers

“…However, most are famous as ectoparasitic bloodsuckers with the best-known "medicinal leeches", which have attracted therapeutic applications for centuries. Several species from the Glossiphoniidae family are also of commercial interests owing to anticoagulative properties of the salivary secretions, antistasin, ghilanten, lefaxin, therostatin, for instance (Siddall et al 2011). Many species feed on fishes and birds, frequently transmitting viruses, bacteria and intracellular parasites, thus triggering diseases.…”