Pathogens or Symbionts? A study of the slime mold Cavenderia aureostipes var. Helvetia and its associated bacteria




Ruff, Kara

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The model organism Dictyostelium discoideum (D. discoideum) has been found to have an endosymbiotic relationship with Burkholderia sp. that confers novel traits to the Dictyostelid; however, investigations into whether or not other Dictyostelids have symbiotic relationships with bacteria have not been conducted. In our study, the Dictyostelid cellular slime mold Cavenderia aureostipes var. Helvetia (C. aureostipes var. Helvetia) was collected from the wild, and it was found to have five bacterial species associated with it. Three of these, Achromobacter species 1 and 2, and Escherichia coli strain 1 (E. coli strain 1) were culturable, and their relationship with C. aureostipes var. Helvetia was investigated. Achromobacter species 1 and 2 were found to be most closely related to Achromobacter xylosoxidans strain I2_5 and Achromobacter piechaudii strain B4b52 while E. coli strain 1 was found to be most closely related to Escherichia coli strain CAU10007. The location of the bacteria was investigated using TEM, the edibility of the bacteria was tested in an edibility assay, and the effect of bacterial cell free supernatant on sori production was analyzed. Micrographs showed that there were no bacteria contained within the spores, and aggregations of bacteria in a biofilm like substance could be viewed only on the outer surface of stalk cells. A. xylosoxidans is known to be able to produce biofilms, and that may be how these bacteria persist during propagation though multiple social cycles. The edibility assay revealed Achromobacter species 1 had poor edibility, Achromobacter species 2 was inedible, and E. coli strain 1 was even less edible than Achromobacter species 2. The resistance to phagocytosis of E. coli strain 1 may be attributed to virulence genes. The results regarding the effect of bacterial cell free supernatant revealed no significant difference in number of sori produced per square centimeter. Overall, we conclude that these bacteria are not endosymbionts as Burkholderia was discovered to be for D. discoideum, and there was no effect of bacterial cell-free supernatant on the sori production of C. aureostipes var Helvetia. Our results also indicate that these bacteria are not a preferred food source, and that E. coli strain 1 may have developed mechanisms to resist phagocytosis, and possibly be pathogenic toward C. aureostipes var Helvetia.



Slime mold, endosymbionts, bacterial symbionts, symbiotic relationship, dictyostelid