Marie-Pierre Crassous

Motility and autotoxicity in Karenia mikimotoi (Dinophyceae)

Karenia mikimotoi is one of the most common red-tide dinoflagellates proliferating in the eastern North Atlantic and around Japan. Kills of marine fauna are associated with its blooms. In mixed water columns it migrates vertically, while in stratified water columns, the population remains confined within pycnocline layers. Wind events, increasing mixing and agitation initiate declines in its populations. This paper is focused on the formulation of mortality rate relative to shear rate. Autotoxicity is demonstrated by the use of a synthetic toxin. Bioconvection observed in cultures allows the establishment of a trade-off between phototropism, which leads to the local accumulation of cells, and their autotoxicity, which would prevent cell concentration. The combination of these processes allows diffusion of the toxin into the underlying water, where it subsequently degrades. Confinement of the population in the pycnocline layer results also from another trade-off between growth conditions and shear-rate-modulated mortality. A simplified encounter kernel was introduced into the population dynamics equation to account for a mortality factor. Under realistic forcing conditions with a small number of parameters, this model reproduced the confinement of the population in the pycnocline layer, the proper timing and the duration of the recurrent K. mikimotoi bloom on the Ushant front (France).

A haemolytic test to assay toxins excreted by the marine dinoflagellate Gyrodinium cf. Aureolum

Abstract The haemolytic properties of phytoplankton toxins have been already demonstrated in many red tides. Although the detection of red blood cell (RBC) lysis is straightforward, it is not always easy to choose the most suitable type of RBC and incubation time. We have investigated these two points in order to obtain reproducible and quantifiable results, by applying the test to known haemolytic molecules. The dose-response curve is sigmoidal. The spiking technique allows a lowering of the detectable haemolytic threshold. Saponin and Kanagawas haemolysin were used. Without previous concentration, the detection limit was at 4000 HU 1 −1 . A chloroform-methanol extraction allowed the detection limit to be lowered to 0.1 HU 1 −1 . This method has been applied to the detection of a marine dinoflagellate whose exotoxin is haemolytic. It may be used for in situ detection of any haemolytic substance.

Direct and fast detection of Alexandrium minutum algae by using high frequency microbalance.

In this paper, a simple detection of a toxic algae, Alexandrium minutum, was developed using highly sensitive quartz crystal microbalance. In terms of performance, compared with other conventional analytical tools, the main interest of our immunosensor is based on a fast and direct detection of these living cells. This system requires the use of one monoclonal antibody directed against the surface antigen of A. minutum. We demonstrate that the whole living and motile algae are caught and detected. The high specificity of the biosensor is also demonstrated by testing several other dinoflagellate species. The frequency shift is correlated to the A. minutum cell concentration. This simple system is potentially promising for environmental monitoring purposes.

Toward detection of harmful algae blooms by in situ surface plasmon resonance spectroscopy

Among marine algae species, Alexandrium minutum produces a phycotoxin called paralytic shellfish poisoning (PSP) that is introduced in the food chain through the ingestion of phytoplankton by shellfishs, and later by human consumers. Thus, in situ monitoring of A. minutum proliferation in coastal seawater is of great economical importance for marine resources exploitation. Here, we propose a rapid test for the detection of A. minutum by surface plasmon resonance spectroscopy. First, whole genomic DNA is extracted from the algae. Second, a 677 bp long portion of the 28S ribosomal DNA is amplified by PCR. Third, the PCR product is detected by surface plasmon resonance spectroscopy onto a DNA functionalized gold substrate.

Toward in situ detection of algae species

For the last few years there is a more and more pressing need to develop system for detecting HAB at their early stage. Researchers have then been working on new in situ sensor. In this paper a submarine transducer based on surface plasmon resonance is reported. It demonstrated a refractive index resolution of 3.10−6, which is promising for later phytoplankton detection.