Date of Award

May 2024

Degree Type

Thesis

Degree Name

Master of Science

Department

Freshwater Sciences

First Advisor

Sandra McLellan

Committee Members

Harvey Bootsma, Gyaneshwar Prasad

Keywords

beaches, E. coli, freshwater, GFP, nutrients

Abstract

Escherichia coli (E. coli) are popular fecal indicator bacteria (FIB) used by many beach management programs in Wisconsin to evaluate the health risks posed by beaches. Prolonged survival of E. coli in beach sand undermines beach management practices that rely on FIB enumeration in surface water because sand and water are routinely mixed through wave action. Studies have shown that sand is a favorable environment for E. coli due to temperature, moisture, nutrient content, and protection from UV radiation. In addition, some sources of E. coli pose significantly less of a threat to human health than human fecal waste, but culture methods cannot determine the source of the pollution. In our project we further investigated why sand serves as a favorable environment for E. coli through field sampling of six Wisconsin freshwater beaches throughout the Summer of 2023. We determined the E. coli and nutrient concentrations in berm sand and surface water samples. Overall, E. coli and nutrient concentrations in berm sand were not significantly different across the six beaches. However, we determined that there are large and small-scale regional factors that can cause some beaches to have high bacteria and nutrient burdens, such as rainfall, beach size, and beach topography. In addition, we examined the molecular response of E. coli to nutrient modulation in beach sand using laboratory microcosms with E. coli constructs that produce GFP in response to nutrient limitation. The constructs were extensively validated through sequencing and microbiological techniques before deployment in microcosms. Nutrient data acquired in the first part of this study, combined with the response of the constricts in beach sand, support our determination that sand is a nutrient deficient environment for E. coli. The sand-model system used in this study has the potential to be used to investigate prolonged survival of E. coli in sand due to the presence of nutrient sources, such as the freshwater algae Cladophora. The results of this study not only inform the beach management programs of the sampled beaches about the E. coli and nutrient status of their beach, but also adds to our scientific understanding of E. coli survival in secondary environments.

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