Shoreline Drying of Microseira (Lyngbya) wollei Biomass Can Lead to the Release and Formation of Toxic Saxitoxin Analogues to the Water Column

Abstract

The harmful, filamentous cyanobacteria Microseira (Lyngbya) wollei produces several toxic analogues of saxitoxin (Lyngbya wollei toxins 1–6, or LWTs 1–6), grows in shallow water, and can deposit significant biomass on nearby shorelines. Here, we show that the LWTs are stable in the biomass during subsequent drying but that the process facilitates the later release of LWTs upon return to the water column. Under basic conditions, LWTs hydrolyzed to generate products that were significantly more neurotoxic than the initial toxins. Aqueous LWTs were subjected to conditions of covarying temperature and pH, and their degradation rates and products were determined at each condition. LWTs 1, 5, and 6 degraded faster at pH ≥ 8 at all temperatures. Their degradation products, which included decarbamoyl saxitoxin and LWT 4, were consistent with a base-catalyzed hydrolysis mechanism and represented a net increase in total biomass toxicity normalized against the equivalent toxicity of saxitoxin. The corresponding pre-exponential terms and activation energies for hydrolysis were obtained for pH 6–10 over the temperature range 10–40 °C. A locally weighted scatterplot smoothing (LOWESS) regression was developed to predict the loss of parent toxins and subsequent products in the water column under conditions corresponding to those commonly encountered in cyanobacterial blooms.

Water Analysis: Emerging Contaminants and Current Issues

“…For example, Metz et al reported that shoreline drying of Microseira (Lyngbya) wollei biomass can lead to the release and formation of toxic Lyngbya wollei toxins (LWTs) to the water column. 220 These toxins are low molecular weight, are structurally similar to saxitoxins, and have 6 congeners that have been reported in the environment. These LWTs were found to be stable in the dried biomass on the shore but could later release into waters when they rise again.…”

“…Several interesting fate and transport studies of algal toxins were published. For example, Metz et al reported that shoreline drying of Microseira (Lyngbya) wollei biomass can lead to the release and formation of toxic Lyngbya wollei toxins (LWTs) to the water column . These toxins are low molecular weight, are structurally similar to saxitoxins, and have 6 congeners that have been reported in the environment.…”

Watershed Development and Eutrophying Potable Source-Water Reservoirs in a Warming Temperate/Subtropical Region

“…By 2019, more than 200 distinct benthic mats of M. wollei covered up to 60% of the total shoreline with ~5 × 10 6 kg of biomass that exceeded 10 kg m −2 in some areas [230,231]. Mats that drift into the shore and dry along the shorelines can release potent toxins into the adjacent water column [232]. For this harmful alga, legacy sediment P is much more important than water-column nutrient supplies; in fact, legacy sediment P was the only factor that realistically predicted its observed massive growth [231].…”

Microseira wollei (M. wollei) blooms in freshwater ecosystems in Lake St. Clair (Michigan, USA)–impacts and possible management approaches

“…This cyanobacterium was renamed because of the establishment of a new phylogenetically distinct genus, Microseira from Lyngbya (Kenins 2017). The biphasic filamentous cyanobacterium, M. wollei, is common worldwide and occurs in a diverse array of aquatic systems (e.g., rivers, lakes, springs) in both freshwater and brackish conditions (Metz et al 2022.). This cyanobacterium has previously been named Plectonema wollei, Lyngbya wollei, and Microseiria wollei (Hudon et al 2014;Metz et al 2022).…”

“…The biphasic filamentous cyanobacterium, M. wollei, is common worldwide and occurs in a diverse array of aquatic systems (e.g., rivers, lakes, springs) in both freshwater and brackish conditions (Metz et al 2022.). This cyanobacterium has previously been named Plectonema wollei, Lyngbya wollei, and Microseiria wollei (Hudon et al 2014;Metz et al 2022). M. wollei is historically known within the southeastern US, but its occurrence is becoming increasingly widespread across the eastern US and southern Canada (Putman et al 2022).…”