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Susanne DiSalvo
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Burkholderia Symbionts of Social Amoebae 

Infection Dynamics:

A central project in the lab is to understand the interaction between Dictyostelium discoideum amoebae and their Burkholderia bacterial symbionts. These Burkholderia symbionts fall into three novel groups (putative species: B. agricolaris, B. hayleyella, and B. bonniea) which are all capable of intracellularly infecting amoebae hosts, but appear to have distinct infectious properties and result in distinct host outcomes. Currently we are trying to characterize these properties using multiple bacterial strains for each species group. Through this characterization, we are examining the consistency of traits within species and exploring potential patterns between infection perameters and host outcomes.


Burkholderia Symbiont Host Range:

We are determining the host range of our D. discoideum associated Burkholderia symbionts across a variety of closely related social amoebae. For this project, we want to determine whether some Burkholderia symbiont strains are specialists or generalists, whether there are infectious characteristics associated with these strategies, and what consequence Burkholderia exposure has to different slime mold species according to their infectious capacity. Finally, we wish to use this system to explore cross-species transmission.


Contextual Modifiers of Symbiotic Outcomes:

Burkholderia infections can have distinct outcomes on host fitness depending on the environmental context. For instance, some Burkholderia strains induce secondary bacterial colonization of amoebae hosts throughout the social stage. This can lead to the carraige of bacterial food during dispersal of host spores, resulting in a fitness advantage in food scarce dispersal conditions (and a disadvantage in food rich conditions). In addition to better characterizing this secondary colonization trait, we are continuing to examine whether and how other environmental conditions modify host-symbiont outcomes.


Burkholderia Specific Bacteriophages:

We have isolated several bacteriophages that infect some of our Burkholderia symbiont strains. Currently, we are characterizing these bacteriophages and testing their impact on the association between Burkholderia and D. discoideum. First, we are examining whether lytic bacteriophages can eliminate or reduce Burkholderia infections in the amoebae host (phage therapy). We are also exploring potential trade-offs between phage resistance and symbiotic ability. In the future, we would also like to explore the presence and role of lysogenic phages in Burkholderia symbionts.


Unculturable Symbionts of Dictyostelium 

Neochlamydia and Amoebophilus:

During our postdoctoral work (in the Strassmann-Queller (QS) lab at WashU), Dr. Tamara Haselkorn and I discovered that approximately half of the QS collection of wild D. discoideum isolates are infected with unculturable bacterial symbionts. According to 16s rRNA sequences, these unculturables are related to Neochlamydia and Amoebophilus symbionts found in other free-living amoebae such as Acanthameoba and Hartmannella. We are currently trying to understand the impact (if any) these infections have on their amoebae hosts.


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