Quantification of Toxic Microcystis spp. during the 2003 and 2004 Blooms in Western Lake Erie using Quantitative Real-Time PCR
and
Received for review November 10, 2004
Revised manuscript received February 10, 2005
Accepted March 21, 2005
In August
of 2003 and August of 2004, blooms of potentially toxic cyanobacteria Microcystis spp. persisted in western Lake Erie. Samples collected from the bloom were analyzed for the cyanobacterial toxin
microcystin and the presence of Microcystis
spp. cells. Estimates of microcystin toxicity exceeding 1 
g L-1
(microcystin-LR activity equivalents), the safety limit set by the World Health
Organization, were found from the samples in both 2003 and 2004. The presence
of Microcystis spp. in water
samples was confirmed through standard polymerase chain reaction (PCR) using a
combination of four primer sets. Quantification of Microcystis was accomplished by a real-time PCR assay
utilizing specific primer-Taq-man probe sets targeted on a conserved, Microcystis-specific 16S rDNA fragment and
a microcystin toxin synthetase gene mcyD.
This approach allowed us to specifically study the distribution and abundance
of toxic Microcystis in the lake
in contrast to previous studies that have assessed Microcystis populations with less refined methods. On the
basis of quantification by quantitative real-time PCR analysis, the total
abundance of Microcystis cells in
the bloom area varied from 4 × 108 to 2 × 103 cells L-1.
The results of this study provide novel insight regarding the distribution and
abundance of Microcystis spp. in
the western basin of Lake Erie, a region plagued in recent years by large-scale
(>20 km2) blooms. Our results suggest that the Maumee River and
Bay may serve as a source for Microcystis
to western and central Lake Erie.