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The contribution of microbiome communities in the gut of the mealybug Pseudococcus jackbeardsleyi to the detoxification of cocaine and other tropane alkaloids

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  • Full or part time
    Dr John D'Auria
    Prof J Gershenzon
  • Application Deadline
    No more applications being accepted
  • Competition Funded PhD Project (Students Worldwide)
    Competition Funded PhD Project (Students Worldwide)

About This PhD Project

Project Description

Background: Very little data exists regarding how a natural herbivore adapts to a host that is producing toxic defensive metabolites. Phloem feeding herbivores have been poorly studied in this regard. Tropane alkaloids are a class of bicyclic compounds found in plants. The alkaloids present in the phloem are typically toxic and serve as a natural pesticide; however, coca-feeding mealybugs survive on the phloem without any apparent negative effects. Recent results from the D’Auria lab have found natural mechanisms for tropane breakdown in mealybugs that are members of the family Pseudococcidae. Certain mealybugs are natural pests of coca plants, Erythroxylum coca and Erythroxylum novogranatense, feeding on phloem exudates from these plant species. In addition to understanding the chemical ecology of this interaction, our lab is interested in the possibility to exploit detoxification mechanisms for their medical treatment potential.

Project Description: The current hypothesis of the D’Auria lab is that microorganisms present within the guts of the mealybugs possess the ability to detoxify tropane alkaloids. Evidence for this interaction was obtained in the following set of experiments: Mealybugs were homogenized in a methanol solution, and mass spectrometry was used to determine the composition of the sample for comparison with standard spectra of metabolites related to known cocaine breakdown products. Furthermore, after surface sterilization, mealybugs were once again homogenized in nutrient broth, and their microbiota were grown in culture. The gut microbiota was cultured on plates containing several tropane alkaloids as the sole carbon source, and five different colonies with distinct morphologies were observed.

The IMPRS doctoral candidate would be responsible for the chemical analysis of breakdown products found in the bacteria after having fed on a host of tropane alkaloids. We envision performing experiments in which the bacteria are grown in the presence and in the absence of alkaloids to pinpoint any inducible detoxification mechanisms. Stable isotope labeling experiments will be used to follow the metabolites as they are processed. In addition, analysis of transcriptome and genome data obtained from the different isolates will be used to identify potential genes and their respective enzymes that participate in the metabolism of the alkaloids. This data will be combined with proteomic studies performed on the same isolates. All enzymes identified during this project will be fully biochemically characterized. This characterization will include enzyme assays, kinetics, and protein structure studies. We would like to prove the biological function of these detoxifying microorganisms by manipulating the microbiome.

Candidate profile: An ideal candidate will first and foremost have the desire to be part of a close-knit team who are passionate about science and learning. Useful skills to possess includes knowledge in molecular biology, biochemistry, and analytical chemistry, however, a deficit in one category should not hinder the successful candidate.


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