Speaker
Description
Symbiotic relationships between unicellular eukaryotes (protists) and endosymbiotic bacteria are widespread, unexpectedly diverse, dynamic and have been established independently many times. We explore the interactions between intracellular rickettsiae, chlamydiae, and holosporacea and diplonemids, which are extremely diverse, abundant yet understudied free- living marine flagellates. While some diplonemids have no endosymbionts, others host one or even two bacterial species. Interestingly, these endosymbionts can be quite easily removed from and reintroduced into their host, without a growth effect in culture. However, when aposymbiotic diplonemids originally hosting chlamydiae and holosporacea are first infected with chlamydiae, it is impossible to subsequently introduce holosporacea, and the same applies vice versa, a strong indication of protective endosymbiosis. We are also exploring metabolic alterations between the symbiotic and aposymbiotic diplonemids. We propose that diplonemids may serve as vectors for chlamydial pathogens of marine fish. In another endosymbiotic system, we study cytoplasmic β-proteobacteria in the parasitic trypanosomatid flagellates of the genera Angomonas, Strigomonas, Kentomonas and Novymonas. While some endosymbionts can be eliminated when the culture medium is supplemented with heme, most relationships are permanent, as the bacteria provide essential nutrients such as amino acids, purines, vitamins, and heme to their hosts. In some cases, the host keeps a single bacterium per cell, while other flagellates exercise no tight control, resulting in a variable number of bacteria per the protist host. We are in the process of functional characterization of several host genome-encoded proteins that have been neo- functionalized in order to control the number and intracellular position of the endosymbionts.
