| Water
Res. 2007 Aug;41(16):3649-3654. Epub 2007 Apr
23.
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Population structure of Cladophora-borne Escherichia
coli in nearshore water of Lake Michigan.
Byappanahalli
MN, Whitman
RL, Shively
DA, Ferguson
J, Ishii
S, Sadowsky
MJ.
United States Geological Survey, Lake Michigan Ecological Research Station,
Porter, IN 46304, USA.
We previously reported that the macrophytic green alga Cladophora harbors
high densities (up to 10(6) colony-forming units/g dry weight) of the fecal
indicator bacteria, Escherichia coli and enterococci, in shoreline waters
of Lake Michigan. However, the population structure and genetic relatedness
of Cladophora-borne indicator bacteria remain poorly understood. In this
study, 835 E. coli isolates were collected from Cladophora tufts (mats)
growing on rocks from a breakwater located within the Indiana Dunes National
Lakeshore in northwest Indiana. The horizontal fluorophore enhanced rep-PCR
(HFERP) DNA fingerprinting technique was used to determine the genetic
relatedness of the isolates to each other and to those in a library of
E. coli DNA fingerprints. While the E. coli isolates from Cladophora showed
a high degree of genetic relatedness (92% similarity), in most cases, however,
the isolates were genetically distinct. The Shannon diversity index for
the population was very high (5.39). Both spatial and temporal influences
contributed to the genetic diversity. There was a strong association of
isolate genotypes by location (79% and 80% for lake- and ditch-side samplings,
respectively), and isolates collected from 2002 were distinctly different
from those obtained in 2003. Cladophora-borne E. coli isolates represented
a unique group, which was distinct from other E. coli isolates in the DNA
fingerprint library tested. Taken together, these results indicate that
E. coli strains associated with Cladophora may be a recurring source of
indicator bacteria to the nearshore beach. |
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