This project was done in collaboration with Mark Siddall, also here at the AMNH.
It began with a simple question. It was known that some groups of leeches had bacteria in specialized structures called mycetomes, but what were these bacteria?
Some photos of the bacteria- on the left are TEM images, on the right is an image of a dissected leech with mycetomes (M) and salivary glands (SAL) labeled.
They turned out to be:
Below are fluorescent in situ hybridization (FISH) images of the bacteria in Placobdella leeches, including, on the right, juveniles which had not yet fed on blood.
Two other groups of leeches also have "mycetome" structures where bacteria are housed. One is the genus, Haementeria, which has 4 globular sacs.
The other is the genus Placobdelloides, which has an esophogeal organ, a cluster of cells surrounding the esophagus. The type species, P. jaegerskieoldi, lives in the rectal region of hippos.
The symbionts from these two groups of leeches turned out to be gammaproteobacteria instead.
A FISH picture of the Placobdelloides symbionts, hybridized with a gammaproteobacterial probe.
This work, combined with that of Joerg Graf and others, means that leeches have forged partnerships with bacteria at least 4 times over their evolutionary history.
