Impact of pesticides on marine coral reef foraminifera.

Our laboratory study looked into how pesticides affect the foraminifera species Heterostegina depressa and their obligatory algal endosymbionts. We incubated the foraminifera separately with different types of pesticides at varying concentrations (1 %, 0.01 % and 0.0001 %); we included the insecticide Confidor© (active substance: imidacloprid), the fungicide Pronto©Plus (tebuconazole), and the herbicide Roundup© (glyphosate). Our evaluation focused on the symbiont's photosynthetically active area (PA), and the uptake of dissolved inorganic carbon (DIC) and nitrogen (nitrate) to determine the vitality of the foraminifera. Our findings showed that even the lowest doses of the fungicide and herbicide caused irreparable damage to the foraminifera and their symbionts. While the insecticide only deactivated the symbionts (PA = 0) at the highest concentration (1 %), the fungicide, and herbicide caused complete deactivation even at the lowest levels provided (0.0001 %). The fungicide had the strongest toxic effect on the foraminiferal host regarding reduced isotope uptake. In conclusion, all pesticides had a negative impact on the holosymbiont, with the host showing varying degrees of sensitivity towards different types of pesticides.

A Model of F-actin Organization in Granuloreticulopodia in Foraminifera: Morphogenetic and Evolutionary Implications from Novel Fluorescent and Polarised Light Observations.

Foraminifera are a group of mostly marine protists that form highly dynamic granular pseudopodia. Recent live experiments on foraminifera labelled with SiR-actin show that F-actin structures are involved in the morphogenesis of granuloreticulopodia and that pseudopodia contain small, motile granules referred to as SiR-actin-labelled granules (ALGs). They may either represent staining artifacts or an unusual form of organisation of actin filaments. To address this problem, we performed double staining of F-actin in fixed specimens of foraminifera using two fluorescent probes (SiR-actin and Phalloidin Atto 488) and analysed the level of co-localisation of their fluorescent signals. Additionally, we performed observations in polarised light to identify birefringence. The images obtained demonstrate similar staining patterns with both probes and birefringence in areas showing intensive fluorescence, thus, ALGs can no longer be considered as staining artifacts. They represent naturally occurring granular structures that contain F-actin and/or are actin-coated. ALGs likely contain F-actin that may play a role in endo-/exocytosis, pseudopodial movement, and/or in intracellular transport. We present a model, explaining their formation and possible functions in relation to other subcellular components. ALGs most likely consist of the adaptation involved in the morphogenesis of granular pseudopodia that predates in phylogeny the occurrence of the shell in foraminifera.