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Hundreds of thousands of people die annually from malaria; a protozoan of the genus Plasmodium is responsible for this mortality. The Plasmodium parasite undergoes several life stages within the mosquito vector, the transition between which require passage across the lumen of the mosquito midgut. It has been observed that in

Hundreds of thousands of people die annually from malaria; a protozoan of the genus Plasmodium is responsible for this mortality. The Plasmodium parasite undergoes several life stages within the mosquito vector, the transition between which require passage across the lumen of the mosquito midgut. It has been observed that in about 15% of parasites that develop ookinetes in the mosquito abdomen, sporozoites never develop in the salivary glands, indicating that passage across the midgut lumen is a significant barrier in parasite development (Gamage-Mendis et al., 1993). We aim to investigate a possible correlation between passage through the midgut lumen and drug-resistance trends in Plasmodium falciparum parasites. This study contains a total of 1024 Anopheles mosquitoes: 187 Anopheles gambiae and 837 Anopheles funestus samples collected in high malaria transmission areas of Mozambique between March and June of 2016. Sanger sequencing will be used to determine the prevalence of known resistance alleles for anti-malarial drugs: chloroquine resistance transporter (pfcrt), multidrug resistance (pfmdr1) gene, dihydropteroate synthase (pfdhps) and dihydrofolate reductase (pfdhfr). We compare prevalence of resistance between abdomen and head/thorax in order to determine whether drug resistant parasites are disproportionately hindered during their passage through the midgut lumen. A statistically significant difference between resistance alleles in the two studied body sections supports the efficacy of new anti-malarial gene surveillance strategies in areas of high malaria transmission.

ContributorsPhillips, Keeley Isabella (Author) / Huijben, Silvie (Thesis director) / Gile, Gillian (Committee member) / Young, Steven (Committee member) / School of Life Sciences (Contributor) / Barrett, The Honors College (Contributor)
Created2021-05
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Biocrusts are microbial communities that inhabit arid soil surfaces, providing essential services to dryland ecosystems. A paradoxical filamentous cyanobacterium, Microcoleus vaginatus, resides within the biocrust. While is often pioneers the colonization of bare, nutrient-poor desert soils worldwide, it cannot fix dinitrogen. In nature, M. vaginatus coexists with a unique microbial

Biocrusts are microbial communities that inhabit arid soil surfaces, providing essential services to dryland ecosystems. A paradoxical filamentous cyanobacterium, Microcoleus vaginatus, resides within the biocrust. While is often pioneers the colonization of bare, nutrient-poor desert soils worldwide, it cannot fix dinitrogen. In nature, M. vaginatus coexists with a unique microbial community, a “cyanosphere”, that is characterized by a high abundance of diazotrophic heterotrophs. This suggests mutualistic relationships wherein nutrients are traded between phototrophs and heterotrophs. To explore these relationships, I performed targeted, pedigreed isolation of cyanosphere members and used co-cultivation to recreate the mutualism in culture. Results showed that, in the absence of fixed nitrogen, M. vaginatus grew well when co-cultured with cyanosphere diazotrophs, but only poorly or not at all when alone or with non-cyanosphere diazotrophs. In agreement with this, the experimental provision of nitrogen to natural populations resulted in a loss of diazotrophs from the cyanosphere compared to controls, but the addition of phosphorus did not. Additionally, the convergence of M. vaginatus trichomes into large bundles held by a common sheath was elicited in culture by the addition of cyanosphere diazotrophs, pointing to a role of cyanobacterial motility responses in the development of mutualistic interactions. I then demonstrated that the tendency of M. vaginatus to stay within bundles and close to the sheath-dwelling cyanosphere was dependent on the cyanosphere population size. This effect was likely mediated by glutamate that acted as a signaling molecule rather than as a N source and impacted the gliding speed and negative chemophobic responses on the cyanobacterium. Glutamate seems to be used as a cue to spatially optimize cyanobacterium-cyanosphere mutualistic exchanges. My findings have potential practical applications in restoration ecology, which I further pursued experimentally. Co-inoculation of soil with cyanosphere diazotrophs resulted in swifter development of biocrusts over inoculation with the cyanobacterium only. Further, their addition to disturbed native soils containing traces of cyanobacteria sufficed for the formation of cohesive biocrusts without cyanobacterial inoculation. The inclusion of such “biocrust probiotics” in biocrust restoration is recommended. Overall, this body of work elucidates the hitherto unknown role of beneficial heterotrophic bacteria in the initial formation and development of biocrusts.
ContributorsNelson, Corey (Author) / Garcia-Pichel, Ferran (Thesis advisor) / Penton, C. Ryan (Committee member) / Gile, Gillian (Committee member) / Bean, Heather (Committee member) / Arizona State University (Publisher)
Created2021