Degree Granting Department
Biology (Integrative Biology)
Valerie J. Harwood, Ph.D.
Florence I. M. Thomas, Ph.D.
Susan S. Bell, Ph.D.
Gordon A. Fox, Ph.D.
Mya Breitbart, Ph.D.
Enterococcus, clonal structure, population dynamics, microbial ecology, microbial resuspension
Enterococci are fecal indicator bacteria (FIB) that are used worldwide for water
quality assessment. However, evidence of high densities and extended survival of
enterococci in sediments and submerged aquatic vegetation (SAV) has caused uncertainty
about their reliability in predicting human health risks from recreational activities in
environmental waters. To address the concern that sediments and SAV may harbor large
reservoirs of enterococci that can affect water column concentrations, aquatic mesocosms
and environmental sampling were employed to investigate patterns of enterococci
densities and population structure across the Tampa Bay watershed.
In mesocosm experiments and environmental samples, SAV harbored higher
densities of enterococci, per mass of substrate, than sediments, and sediments harbored
higher densities than water. Population structure assessed by BOX-PCR genotyping was
relatively unique in each sample, although slight similarities among samples suggested
grouping primarily by location rather than substrate or season. Strain diversity was
highly variable, and many samples had low diversity, including nearly monoclonal
structure throughout the mesocosm experiments and in several of the environmental
samples. Several strains were highly abundant and cosmopolitan (found across sites,
seasons, and substrates), and may represent highly naturalized and reproducing indicator
bacteria populations that are not directly related to pollution events.
When the enterococci densities were viewed from the perspective of the entire
aquatic system, SAV-associated enterococci did not comprise a major proportion of the
total population, due to the typically large differences in volume of each substrate (SAV
vs. sediments vs. water). Instead, the largest proportions of enterococci were typically
found in the water or the sediments, depending on the relative volume of substrate or the
enterococci density associated with each substrate. Modeling results illustrate that the
relative importance of each substrate in terms of FIB populations can shift dramatically
over time and space due to changes such as vegetation cover, tidal cycles, and bacteria
densities. Furthermore, at several sites within the watershed, estimates of sediment and
bacteria resuspension from sediments were very low, suggesting that this process rarely,
if ever, significantly affects water column concentrations of enterococci in the watershed.
Scholar Commons Citation
Badgley, Brian D., "The Importance of Benthic Habitats as Reservoirs of Persistent Fecal Indicator Bacteria" (2009). USF Tampa Graduate Theses and Dissertations.