The use of qPCR to monitor changes of toxin and non-toxin producing cyanobacteria populations in Vancovuer Lake, WA in response to water quality variables

Background/Question/Methods

The increasing frequency of cyanobacteria harmful algal blooms in freshwater systems has become a commonly recognized problem due to detrimental effects on water quality.  Current research suggests various biotic and abiotic interactions influence toxin production, bloom formation, persistence, and decay in freshwater systems.  Our research objectives were: 1) investigate what environmental variables influence cyanobacteria blooms; 2) examine what environmental variables influence toxin production, specifically microcystin; and 3) analyze changes in environmental variables contribute to the fluctuations observed in toxic and non-toxic producing cyanobacteria.

From 2007 through 2010, we quantified phytoplankton abundance and community composition and measure several environmental variables (i.e. nutrients, temperature, and total lake depth) in Vancouver Lake, Washington.  From 2009 through 2010, intracellular and extracellular microcystin concentrations were measured using an ELISA kit. PCR was used to isolate the mcyA gene in microcystin producing general in lake water samples.  We then used qPCR to quantify the toxin and non-toxin producing cyanobacteria populations, and the overall cyanobacteria population to assess relative abundances during the cyanobacteria bloom. 

Results/Conclusions

Based on phytoplankton community composition, cluster analysis revealed three significantly different cyanobacteria blooms.  In 2007, Microcystis and Anabaena were the most abundant cyanobacteria species present during the summer bloom.  Blooms in subsequent years were dominated by Anabaena and Aphanizomenon.  Non-metric multidimensional scaling revealed that high levels of orthophosphate was the environmental factor most strongly associated with seasonal cyanobacteria blooms. Microcystin concentrations varied throughout the bloom ranging from <1 ppb to 15 ppb in 2009, and approximately 2 ppb to 14 ppb in 2010.  Principal components analysis suggests that intracellular microcystin concentrations were correlated with orthophosphate. Sequenced results of the isolated mcyA gene indicated that Microcystis was the only microcystin-producing species present in 2009 and 2010.  Although we detected microcystin during the summer blooms, Microcystis was visually absent in 2010, and rarely detected in 2009. Preliminary results indicate that the majority of Microcystis population is potentially toxic, and that the total Microcystispopulation rarely exceeds 1% of the overall cyanobacteria population. 

Continuing research will include examining environmental variables influencing toxin and non-toxic cyanobacteria populations and microcystin concentrations.  Our findings will provide new insights into how environmental variables influence phytoplankton community dynamics, generally, and persistence of seasonal toxin cyanobacteria blooms, specifically.  Additionally, our results underscore the importance of using molecular techniques in assessing potentially toxic cyanobacteria blooms.