Microbial
Communities and Fecal Indicator Bacteria Associated with Cladophora
Mats on Beach Sites along Lake Michigan Shores
Ola A. Olapade, Morgan M. Depas, Erika
T. Jensen, and Sandra L. McLellan*
Great Lakes WATER Institute, University of Wisconsin—Milwaukee,
600 E. Greenfield
Avenue, Milwaukee, WI 53204.
Abstract
A high biomasses of Cladophora,
a filamentous green alga, is found mainly during the summer
along the shores of Lake Michigan. In this study, the abundance
and persistence of the fecal indicator bacterium Escherichia
coli and sulfate-reducing bacteria (SRB) on Cladophora
mats collected at Lake Michigan beaches were evaluated using
both culture-based and molecular analyses. Additionally, 16S
rRNA gene cloning and sequencing were used to examine the
bacterial community composition. Overall, E. coli
was detected in all 63 samples obtained from 11 sites, and
the average levels at most beaches ranged from 2,700 CFU/100
g (wet weight) of Cladophora to 7,500 CFU/100 g of Cladophora.
However, three beaches were found to have site average E.
coli densities of 12,800, 21,130, and 27,950 CFU/100
g of Cladophora. The E. coli levels in the
lake water collected at the same time from these three sites
were less than the recommended U.S. Environmental Protection
Agency limit, 235 CFU/100 ml. E. coli also persisted
on Cladophora mats in microcosms at room temperature
for more than 7 days, and in some experiments it persisted
for as long as 28 days. The SRB densities on Cladophora
mats were relatively high, ranging from 4.4 x106
cells/g (6.64 log CFU/g) to 5.73 x106 cells/g (6.76
log CFU/g) and accounting for between 20% and 27% of the total
bacterial counts. Partial sequences of the 16S rRNA gene clones
revealed a phylogenetically diverse community, in which the
Cytophaga- Flavobacterium-Bacteroides cluster and
the low-G+C-content gram-positive bacteria were the dominant
organisms, accounting for 40% and 12.8%, respectively, of
the total clone library. These results further reveal the
potential public health and ecological significance of Cladophora
mats that are commonly found along the shoreline of Lake Michigan,
especially with regard to the potential to harbor microorganisms
associated with fecal pollution and odor-causing bacteria.
Keywords: Cladophora; Escherichia
coli; sulfate-reducing bacteria;16S rRNA gene;Cytophaga-
Flavobacterium-Bacteroides;Bacteria;taxonomy.
Corresponding author: Tel.: (414) 382-1700.
Fax: (414) 382-1705
E-mail: mclellan@uwm.edu |
