Might Recycled Water Inhibit Toxin-Producing Cyanobacteria?

Abstract

Cyanobacteria, or blue-green algae, is a phytoplankton phylum found in surface water bodies worldwide. For decades, blue-green algae has caused severe aesthetic water quality problems and induced water deoxygenation, leading to fish kills and other detrimental outcomes. Furthermore, some cyanobacterial genera, most notably several Microcystis species, are known to produce hepatotoxic peptides known as microcystins. Such toxin production is of critical and increasing public health concern, as hepatotoxic cyanobacterial blooms in freshwater lakes and streams have been implicated in human and animal sickness, and even death. Studies have correlated increased toxin production to enhanced temperature, nutrient concentrations, and light intensity, but research results examining microcystin toxin production in response to environmental stimuli have rarely been conclusive outside of the laboratory or over multiple seasons. Our research implemented advanced molecular techniques (real-time quantitative PCR) to detect and quantify cyanobacterial genes (CYAN) and toxin synthetase genes (mcyD) in water samples collected from a recycled water retention pond and a groundwater-filled pond. Water samples also underwent chemical and physical analyses to identify factors correlating to decreased toxin synthesis. Our results show similar concentrations of CYAN in both ponds but lower concentrations (sometimes below limits of detection) of mcyD levels in the recycled water retention pond. LC-MSMS showed average toxin concentrations of 6.702 ± 0.067 µg L-1 in the groundwater-filled pond while toxins were undetectable (detection limit ≥ 3 ppt) in the recycled water retention pond. Levels of mcyD in the groundwater pond were negatively correlated (p ≤ 0.05) with Cr52, a find that has been paralleled in previous research. Concentrations of Fe56 were significantly lower in the groundwater pond (p ≤ 0.05), suggesting iron-limitation may have been a contributing factor to microcystin-biosynthesis. Knowledge of the regulation of microcystin toxin biosynthesis may facilitate implementation of water management strategies to avoid environmental conditions that induce dangerous water quality conditions.