Molecular characterization of potential microcystin-producing cyanobacteria in Lake Ontario embayments and nearshore waters

Abstract

The distribution and genotypic variation of potential microcystin (MC) producers along the southern and eastern shores of Lake Ontario in 2001 and 2003 were examined using a suite of PCR primers. Cyanobacterial, Microcystis sp., and Microcystis-specific toxin primer sets identified shoreline distribution of cyanobacterial DNA (in 97% of the stations) and MC synthetase genes (in 50% of the stations). Sequence analysis of a partial mcyA amplicon targeting Microcystis, Anabaena, and Planktothrix species indicated that the Microcystis sp. genotype was the dominant MC genotype present and revealed a novel Microcystis-like sequence containing a 6-bp insert. Analysis of the same samples with genus-specific mcyE primers confirmed that the Microcystis sp. genotype was the dominant potential MC producer. Genotype compositions within embayments were relatively homogenous compared to those for shoreline and tributary samples. MC concentrations along the shoreline exhibited both temporal and spatial differences as evidenced by the protein phosphatase inhibition assay, at times exceeding the World Health Organization guideline value for drinking water of 1.0 microg MC-LReq liter(-1). MC genotypes are widespread along the New York State shoreline of Lake Ontario, appear to originate nearshore, and can be carried through the lake via wind and surface water current patterns.

FIG. 1.

Sampling locations along the New York State border of Lake Ontario separated into regions. Arrows represent the Lake Ontario average annual surface water current pattern. (Adapted from reference with permission of the publisher.)

FIG. 2.

Neighbor-joining trees made using p-distance analysis to show the relationship between partial mcyA genes (∼300 bp) from Lake Ontario embayments in 2001 (A) and 2003 (B). Trees were generated using the program Mega 3.1. Bootstrap values of >75% are displayed at the nodes (1,000 replicates). The scale bar is a measure of the number of substitutions per site. Clone names indicate the embayment and number of clones represented. Reference sequences were obtained from GenBank, with accession numbers shown in parentheses.