Application of molecular techniques for the detection of potentially microcystin-producing organisms in New York State waters

Microcystins are potent hepatotoxins produced by cyanobacteria worldwide. The aim of this study was to determine the feasibility of using molecular probes to easily and accurately detect the potential for microcystin production by targeting the microcystin biosynthetic (mcy) gene cluster. I hypothesized that: (1) mcy genes are correlated to microcystins and can be used to predict sites with a tendency for microcystin production and (2) differences between mcy gene signatures can be used to determine heterogeneity and track potentially microcystin-producing populations. To address hypothesis 1, mcy gene presence and microcystin occurrence were compared in samples collected from Oneida Lake. The mcy genes were detectable prior to elevated microcystin production, however, the mcy gene targets did not always co-occur. To determine a predictive formula for microcystins, physiochemical variables were compared to temporal (Oneida Lake) and spatial (New York State (NYS) sites) variation in microcystin production and potential. Chlorophyll (chl) a was positively correlated with microcystins, both spatially and temporally. Spatial variation in mcy gene presence was correlated with chl a, however, no factor could be correlated with the temporal variation of mcy genes. To address hypothesis 2, mcyA amplicons were cloned and sequenced from samples collected at bloom events on Oneida Lake, and lakeside and shore side samples from Lake Ontario. Microcystis sp. was the dominant mcy genotype detected from both lakes, and a novel Microcystis-like mcyA sequence was identified. This genotypic diversity can be used to track mcy-containing populations. In Oneida Lake, the mcy populations were mixed, and the percentage of clones containing the novel mcyA sequence was higher at elevated microcystin concentrations. In Lake Ontario, the mcy genotype composition within embayments was homogenous compared to shoreline and tributary samples, indicating that embayments harbor separate mcy populations. The exact origin and transport could not be determined due to the large spatial separation of sample sites. Overall, the results obtained suggest that probes targeting mcy genes are both sensitive and robust. Using this approach, monitoring and management programs can determine the dominant genera present containing mcy genes and the factors influencing mcy gene occurrence.;Keywords. cyanobacteria, Lake Ontario, mcy genes, microcystin, Microcystis, Oneida Lake...