Senior Honors Projects, 2010-current

Date of Award

Fall 2015

Document Type

Dissertation/Thesis

Degree Name

Bachelor of Science (BS)

Department

Department of Biology

Advisor(s)

Reid Harris

Eria Rebollar

Abstract

An emerging infectious disease caused by the fungus Batrachochytrium dendrobatidis (Bd) is leading to global amphibian declines and is threatening the biodiversity of amphibians. Bd susceptibility varies among individuals, species, and populations perhaps due to defensive mechanisms such as symbiotic skin microbes. Some species of amphibians such as Craugastor fitzingeri, a terrestrial frog native to Central America, continue to persist in Bd-positive environments in Panama. My study focused on identifying antifungal bacterial isolates and determining the culturability of the bacterial community on 15 individuals of C. fitzingeri. Morphologically distinct isolates were challenged against Bd in inhibition assays to determine an inhibition score for each isolate. The 16S rRNA sequences of all cultured isolates were aligned and grouped in Operational Taxonomic Units (OTUs). The relative abundance of cultured OTUs was compared to that of the entire bacterial community obtained with the culture-independent method. Over 80% of the individuals had at least one morphologically distinct Bd-inhibitory isolate at an inhibition score of 80% or greater. In comparing culturability, the cultured community was significantly more relatively abundant than the entire culture-independent community (Wilcoxon test: W=101130, p= 2.53e-14). Specifically, Cellulomonas, Comamonas testosteroni, and Acinetobacter johnsonii were highly relative abundant and were culturable. However, one relatively abundant species of Pseudomonas was not culturable. Additionally, I was able to culture 17.92% of the total relative abundance within the entire bacterial community. Identifying inhibitory isolates and the relative abundances of culturable OTUs are crucial steps to designing an ideal probiotic to potentially protect amphibian populations from Bd.

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