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Water01 - IMOTOX


Identifying and monitoring of harmful cyanobacteria

Blooms of harmful cyanobacteria have been shown to increase in both frequency and severity due to global warming, particularly through increased nutrient loads at extreme weather events with elevated winter/spring rainfall and flushing events followed by extended periods of summer drought. These blooms threaten our shrinking freshwater resources in several ways: By increasing turbidity and consequently depriving submerged plants of light they suppress invertebrate and fish habitats and can thus affect biodiversity. On the other hand, release of cyanotoxins during blooms can cause problems for fisheries, drinking water reservoirs as well as recreational water activities. As part of the International Graduate School of Science and Engineering (IGSSE), the IMOTOX project team aims to develop a monitoring and early warning system for cyanobacterial blooms, and research factors influencing bloom formation, toxicity and collapse. This will be achieved through a close interaction of molecular microbiology, and remote sensing technology. The early detection of the rise of potentially harmful cyanobacteria in freshwater lakes shall be achieved by remote sensing, followed by a targeted molecular and microbial verification, which in turn will allow time for taking appropriate counter measures.



Research focus of the remote sensing part:

To monitor blooms, empirical algorithms based on band ratios or statistical approaches like genetic algorithms can be applied, since blooms are usually dominated by a single species. However, such algorithms are inherently not universally applicable and need to be tuned to the current situation. A challenge lies in the identification of different groups of phytoplankton under non-bloom conditions, as needed to establish an early warning system. If more than a single species affects the water colour, data analysis must be based on bio-optical models which are able to simulate the measured sensor signal of all bands for all possible concentrations of the optically active components in the water. These models have to be fed with inherent optical properties (IOPs) that characterise the actual water constituents. This is particularly difficult for cyanobacteria, because the IOPs of cyanobacteria are highly variable due to their capability to adapt the concentration and composition of light-harvesting pigments to the light conditions during growth. Therefore, one focus of this project lies on investigating the variability of the absorption and fluorescence properties of cyanobacteria, their parameterisation and implementation into bio-optical models.

Contact: anna.goeritz(at)tum.de (IGSSE - PhD student); Peter.Gege(at)dlr.de (Supervisor at The Institute of Remote Sensing Technologies  (DLR))

Research focus of the microbiology part:

Harmful algal blooms (HABs) are caused by a number of phytoplankton species. In freshwater systems blooms of potentially toxin-producing cyanobacteria are frequently found, particularly of the genera Microcystis, Anabaena and Planktothrix. The most common cyanobacterial toxin present during HABs is the hepatotoxic cyclic peptide microcystin. The genes required for microcystin synthesis are known in several species of microcystin-producing cyanobacteria. However, toxin-producing and non-toxic strains generally co-occur in an aquatic system. Environmental factors that trigger a shift in the population structure and an exponential growth of toxin-producers have been studied intensively over the years. It is generally acknowledged that high temperatures and high nutrient concentrations as well as a change in pH contribute to HAB formation. Biotic factors such as protozoan grazing and viral lysis by cyanophages are influencing the formation of such blooms as well, but their role is far less understood. Of particular interest is the question whether protozoa and cyanophages lead to an increase of toxin concentration by inducing a defence mechanism of the cyanobacteria and releasing toxins by lysing cyanobacterial cells, or whether they could contribute to the collapse of the HAB by decimating the population of toxic cyanobacteria.

Identification and quantification of cyanobacterial species was until recently exclusively based on morphological microscopic analysis. However, morphological differentiation between toxin-producing and non-toxic cyanobacteria strains of the same species is not possible. In this project a molecular approach employing polymerase chain reaction (PCR) and quantitative polymerase chain reaction (qPCR) techniques will be used to target the toxin genes in order to distinguish the strains on the basis of the presence or absence of those genes. Furthermore, qPCR analysis will determine the level of gene transcription and how it is influenced by biotic and abiotic factors. Laboratory experiments will lead to a better understanding of these interactions and field studies in selected lakes will characterize the cyanobacterial population and its toxicity during algal blooms.

Contact: pia.sharma(at)tum.de


Image credits:  

(1) Cyanobacteria bloom in the Baltic Sea – DLR, IMF Status Report 2013

(2) Octocopter – DLR Oberpfaffenhofen

(3+4) Cyanobacteria bloom in the Bergknappweiher near Weilheim, Bavaria – F. Bauer, LSI

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