Graduation Year

2009

Document Type

Dissertation

Degree

Ph.D.

Degree Granting Department

Biology (Integrative Biology)

Major Professor

Valerie J. Harwood, Ph.D.

Co-Major Professor

Florence I. M. Thomas, Ph.D.

Committee Member

Susan S. Bell, Ph.D.

Committee Member

Gordon A. Fox, Ph.D.

Committee Member

Mya Breitbart, Ph.D.

Keywords

Enterococcus, clonal structure, population dynamics, microbial ecology, microbial resuspension

Abstract

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.

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