Joshua Sterling Bentley and Dr. Joel S. Griffitts, Micro and Molecular Biology

vUnderstanding the molecular mechanism permitting symbiosis is not completely understood. A more confounding question is why do closely related bacteria demonstrate variable specificity? In my project we attempted to answer this very question by attempting to identify the gene or genes responsible for the variability.

In order to conduct experiments that would lead us to identifying the genes involved the projected required extensive testing to insure accurate results were being recorded. This wasn’t as easy as we thought it would have been. During the initial testing of hundreds of plants we found out that they were infected by some unknown contaminate giving us invalid results and further postponing the project. Ten different Medicago species were selected to test over 100 bacterial strains on to look for patterns in results. Almost every strain was test twice to ensure accurate results.

We did notice that symbiosis isn’t a clear cut process but rather it is on a continuum. This is believed to be due to different parts of the process being affected differently by each bacterial strain. Because of this we elected it would be best to first study plants at both ends of the continuum. Figure 2 shows the 42 strains elected as models for future study because the covered the spectrum of interactions we were able to view in the initial studies. All but one of the strains that displayed partial symbiosis were eliminated from this group.

The next step in the process was to perform transduction to introduce fragmented genes from a strain that allowed symbiosis into one that did not. In order to do this we were required to insert streptomycin resistance into several strains permitting us to know if the event was successful. This stage went very smoothly and we were able to several colonies from the transductions. The next step that I was unable to perform is to use the new isolates on the five Medicago species to determine if we were able to introduce the genes responsible for symbiosis into a previously ineffective bacterial strain.