ESR10 Regiane Sanches Natumi

Project: Stability of natural toxins in surface waters

Principal supervisor: Dr. Elisabeth ML Janssen

Intro to project:

Cyanobacterial blooms are expanding temporally and spatially, which is promoted by eutrophication and likely climate change. Cyanobacteria can produce a wide range of bioactive compounds with different modes of action, including a variety of toxic cyanopeptides. Hardly any information is available regarding the occurrence, toxicity, and physical-chemical properties of the majority of emerging cyanopeptide classes beyond microcystins. Such information is crucial to assess the risk of these emerging natural toxins reach drinking water supply plants and affect human health. In this context, I focus in my PhD project on the stability and possible photochemical and biological transformation processes of emerging cyanopeptides in surface waters. The final goal of my work is to improve our understanding of the stability of these emerging cyanopeptides in the aquatic system and to improve risk assessment for toxins released during cyanobacterial bloom events.

To reach the final goal, I set the following specific objectives: 1) development of an analytical workflow to detect structurally known cyanopeptides, 2) determination of cyanopeptide production dynamics during cyanobacterial growth; 3) assessment of photochemical transformation for selected cyanopeptides; 4) assessment of biotransformation for selected cyanopeptides in surface waters.

Project status (February 2019):

Thus far, I focused on developing analytical methods (objective 1) and production dynamics (objective 2). I assembled a suspect list with more than 580 cyanopeptides and the analytical procedures for sample preparation and measurement by LC-MS/MS. Furthermore, I developed a comprehensive data analysis workflow for the tentative identification of emerging cyanopeptides for which no reference standard materials exist. With this methodology at hand, I analyzed cyanopeptide co-production dynamics of several cyanobacterial species during different growth phases and under different nutrient conditions. I find varying cyanopeptide profiles depending on the growth conditions and cyanobacterial species. Overall, I tentatively identified more than 90 potential cyanotoxins from the suspect list. These cyanopeptide fingerprints were also analyzed for field samples from lakes in Switzerland that I sampled in 2018 and from the Czech Republic, provided by Masaryk University. We could see that one specie produce more than one family of cyanopeptides and that the same cyanopeptides can be produced by more than one specie. These findings encourage us to take a closer look at the emerging cyanopeptides occurrence and environmental fate in the upcoming work. Preliminary test with exposure to simulated sunlight revealed that some cyanopeptides were rather stable in sunlight while others degraded rapidly.

For the remaining period of my PhD I plan to conduct further photochemistry tests to determine the cyanopeptides photochemical half-lives under simulated sunlight conditions, and to estimate the relative contribution of the various photochemical pathways on the overall decay. While photodegradation may be relevant for some compounds, others may be persistent during sunlight exposure and biotransformation may be the more dominant fate process. Therefore, I will assess aqueous biotransformation rates of selected cyanopeptides in a final state of my PhD work. For photo- and biotransformation tests, I anticipate to search for transformation products to elucidate the reaction pathways where possible.

(Un)fortunately, there is not much known about the toxicity and environmental fate of emerging cyanopeptides, which presents a challenge and at the same time an opportunity to me. There are two main reasons that support the need for a risk assessment of these otherwise poorly studied compounds: First, other cyanopeptides are just as abundant as microcystins because they are co-produced during cyanobacterial bloom events. Second, the other cyanopeptides are bioactive as they are inhibiting enzyme (predominantly proteases). As preliminary tests show that some cyanopeptides are rather stable under environmental conditions, it would be recommended to also assess their toxicity in more detail, work that will be done in collaboration with ESR 14. The knowledge gained through this project will provide necessary information regarding stability of emerging cyanopeptides for risk assessment of cyanobacterial blooms and their potential to reach drinking water supply plants. Furthermore, the new established cyanopeptide suspect list can assist water suppliers and other researchers for the identification of cyanopeptides and facilitate more information regarding their global occurrence