Great Lakes WATER Institute, University of Wisconsin—Milwaukee, Milwaukee, Wisconsin 53204
Received 30 September 2005/ Accepted 3 January 2006
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 x
106 cells/g (6.64 log CFU/g) to 5.73 x
106 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.
Applied and Environmental Microbiology, March 2006,
p. 2287-2289, Vol. 72, No. 3
| SHORT REPORT |
Recovery of Escherichia coli from Soil after
Addition of Sterile Organic Wastes
Adrian Unc,* Julie Gardner, and Susan Springthorpe
University of Ottawa, Centre for Research on Environmental Microbiology, Ottawa, Ontario, Canada
Received 17 June 2005/ Accepted 9 January 2006
Laboratory batch tests indicate that addition of sterile
municipal sewage biosolids to clay soil from four depths increases
the numbers of Escherichia coli isolates recoverable
in EC-MUG broth (EC broth with 4-methylumbelliferyl-ß-glucuronide).
This effect was most marked for the deeper soil layers, with
increases of about 2.6 orders of magnitude in E. coli most
probable number.