Chemical and morphological defenses of Pseudo-nitzschia multiseries in response to zooplankton grazing

First evidence of the induction of domoic acid production in Pseudo-nitzschia australis by the copepod Temora longicornis from the French coast

Diatoms of the genus Pseudo-nitzschia are widespread in marine waters. Some of them can produce the toxin domoic acid (DA) which can be responsible for amnesic shellfish poisoning (ASP) when transferred into the food web. These ASP events are of major concern, due to their ecological and socio-economic repercussions, particularly on the shellfish industry. Many studies have focused on the influence of abiotic factors on DA induction, less on the role of biotic interactions. Recently, the presence of predators has been shown to increase DA production in several Pseudo-nitzschia species, in particular in Arctic areas. In order to investigate the relationship between Pseudo-nitzschia species and grazers from the French coast, exposures between one strain of three species (P. australis, P. pungens, P. fraudulenta) and the copepod Temora longicornis were conducted for 5 days. Cellular and dissolved DA content were enhanced by 1,203 % and 1,556 % respectively after the 5-days exposure of P.australis whereas no DA induction was observed in P. pungens and P. fraudulenta. T. longicornis consumed all three Pseudo-nitzschia species. The copepod survival was not related to DA content. This study is an essential first step to better understanding the interactions between planktonic species from the French coast and highlights the potential key role of copepods in the Pseudo-nitzschia bloom events in the temperate ecosystems.

Exposure to the mixotrophic dinoflagellate Lepidodinium sp. and its cues increase toxin production of Pseudo-nitzschia multiseries

The present study examined the defense responses of toxigenic Pseudo-nitzschia species (P. multiseries) to a mixotrophic dinoflagellate, Lepidodinium sp., and its associated cues. We evaluated their responses to different predation risks, including direct physical contact and indirect interactions facilitated by cues from Lepidodinium sp. during active feeding on heterospecific prey (Rhodonomas salina), limited feeding on conspecific prey (P. multiseries) and non-feeding (autotrophic growth in f/2 medium) states. This study is the first investigation of these trophic interactions. Our results demonstrated a significant increase in cellular domoic acid (cDA) in P. multiseries when exposed to Lepidodinium sp. and its associated cues, which was 1.38 to 2.42 times higher than the non-induced group. Notably, this increase was observed regardless of Lepidodinium sp. feeding on this toxic diatom and nutritional modes. However, the most significant increase occurred when they directly interacted. These findings suggest that P. multiseries evaluates predation risk and increases cDA production as a defensive strategy against potential grazing threats. No morphological changes were observed in P. multiseries in response to Lepidodinium sp. or its cues. P. multiseries cultured in flasks of Group L+P-P showed a decrease in growth, but Group L-P and Group L+R-P did not exhibit any decrease. These results suggest a lack of consistent trade-offs between the defense response and growth, thus an increase in cDA production may be a sustainable and efficient defense strategy for P. multiseries. Furthermore, our findings indicate that P. multiseries had no significant impact on the fitness (cell size, growth and/or grazing) of Lepidodinium sp. and R. salina, which suggests no evident toxic or allelopathic impacts on these two phytoplankton species. This study enhances our understanding of the trophic interactions between toxic diatoms and mixotrophic dinoflagellates and helps elucidate the dynamics of Harmful Algal Blooms, toxin transmission, and their impact on ecosystem health.

Multi-omic insights into the cellular response of Phaeodactylum tricornutum (Bacillariophyta) strains under grazing pressure

Background/Aims

Phaeodactylum tricornutum, a model organism of diatoms, plays a crucial role in Earth's primary productivity. Investigating its cellular response to grazing pressure is highly significant for the marine ecological environment. Furthermore, the integration of multi-omics approaches has enhanced the understanding of its response mechanism.

Methods

To assess the molecular and cellular responses of P.tricornutum to grazer presence, we conducted transcriptomic, proteomic, and metabolomic analyses, combined with phenotypic data from previous studies. Sequencing data were obtained by Illumina RNA sequencing, TMT Labeled Quantitative Proteomics and Non-targeted Metabolomics, and WGCNA analysis and statistical analysis were performed.

Results

Among the differentially expressed genes, we observed complex expression patterns of the core genes involved in the phenotypic changes of P.tricornutum under grazing pressure across different strains and multi-omics datasets. These core genes primarily regulate the levels of various proteins and fatty acids, as well as the cellular response to diverse signals.

Conclusion

Our research reveals the association of multi-omics in four strains responses to grazing effects in P.tricornutum. Grazing pressure significantly impacted cell growth, fatty acid composition, stress response, and the core genes involved in phenotype transformation.

Chemical cues in the interaction of herbivory-prey induce consumer-specific morphological and chemical defenses in Phaeocystis globosa

Bloom-forming algae Phaeocystis globosa is one of the most successful blooming algae in the oceans due to its capacity to sense grazer-associated chemical cues and respond adaptively to these grazer-specific cues with opposing shifts in phenotype. P. globosa produces toxic and deterrent compounds as chemical defenses. However, the origin of the signals and underlying mechanisms that triggered the morphological and chemical defenses remain enigmatic. Rotifer was chosen to establish an herbivore-phytoplankton interaction with P. globosa. The influences of rotifer kairomone and conspecific-grazed cue on morphological and chemical defenses in P. globosa were investigated. As a result, rotifer kairomones elicited morphological defenses and broad-spectrum chemical defenses, whereas algae-grazed cues elicited morphological defenses and consumer-specific chemical defenses. According to multi-omics findings, the difference in hemolytic toxicity caused by different stimuli may be related to the upregulation of lipid metabolism pathways and increased lipid metabolite content, while the inhibition of colonial formation and development of P. globosa may be caused by the downscaled production and secretion of glycosaminoglycans. The study demonstrated that zooplankton consumption cues were recognized by intraspecific prey and elicited consumer-specific chemical defenses, highlighting the chemical ecology of herbivore-phytoplankton interactions in the marine ecosystem.

Costs and benefits of predator-induced defence in a toxic diatom

Phytoplankton employ a variety of defence mechanisms against predation, including production of toxins. Domoic acid (DA) production by the diatom Pseudo-nitzschia spp. is induced by the presence of predators and is considered to provide defence benefits, but the evidence is circumstantial. We exposed eight different strains of P. seriata to chemical cues from copepods and examined the costs and the benefits of toxin production. The magnitude of the induced toxin response was highly variable among strains, while the costs in terms of growth reduction per DA cell quota were similar and the trade-off thus consistent. We found two components of the defence in induced cells: (i) a 'private good' in terms of elevated rejection of captured cells and (ii) a 'public good' facilitated by a reduction in copepod feeding activity. Induced cells were more frequently rejected by copepods and rejections were directly correlated with DA cell quota and independent of access to other food items. By contrast, the public-good effect was diminished by the presence of alternative prey suggesting that it does not play a major role in bloom formation and that its evolution is closely associated with the grazing-deterrent private good.

Harmful algae and climate change on the Canadian East Coast: Exploring occurrence predictions of Dinophysis acuminata, D. norvegica, and Pseudo-nitzschia seriata

Harmful algal blooms (HABs) are a threat to human health, local economies, and coastal ecosystems. Generalized additive mixed models (GAMMs) were fitted using a 24-y database in order to predict future occurrences of three distinct species of HABs on the Canadian East Coast, the dinoflagellates Dinophysis acuminata and D. norvegica, and the diatom Pseudo-nitzschia seriata. GAMMs produced for each species were combined with two downscaled climate simulations (MPI-ESM-LR and CanESM2) under the representative concentration pathway (RCP) 8.5 over the 21st century. D. acuminata, D. norvegica, and P. seriata GAMMs were fitted using sea surface salinity and sea surface temperature, with wind speed averaged over seven days added to the P. seriata model. GAMMs succeeded at various degrees at reproducing past HAB events, with D. acuminata and D. norvegica being accurately modelled, and P. seriata producing less precise model results. Both climate simulations lead to similar conclusions in regards to the spatio-temporal shift in occurrences of the three studied species. D. acuminata and D. norvegica blooms (≥ 1000 cells L ^- 1) are predicted to increase in the future, whereas P. seriata bloom events (≥ 5000 cells L ^- 1) will tend to stabilise/decrease overall on the Canadian East Coast. Dinophysis blooms are most likely to increase in the St. Lawrence Estuary. Pseudo-nitzschia blooms will move to the northeastern part of the Gulf of St. Lawrence and will increase in the Bay of Fundy/Gulf of Maine regions. On average, earlier blooms and larger seasonal windows of opportunity are predicted across all species investigated. We conclude that changes in D. acuminata, D. norvegica, and P. seriata bloom dynamics and their spatial distributions could threaten aquaculture industries and ecosystem health on Canada's East Coast in localities and during seasons which were not previously impacted by these species.

Toxicity of the Diatom Genus Pseudo-nitzschia (Bacillariophyceae): Insights from Toxicity Tests and Genetic Screening in the Northern Adriatic Sea

Diatoms of the genus Pseudo-nitzschia H.Peragallo are known to produce domoic acid (DA), a toxin involved in amnesic shellfish poisoning (ASP). Strains of the same species are often classified as both toxic and nontoxic, and it is largely unknown whether this difference is also genetic. In the Northern Adriatic Sea, there are virtually no cases of ASP, but DA occasionally occurs in shellfish samples. So far, three species-P. delicatissima (Cleve) Heiden, P. multistriata (H. Takano) H. Takano, and P. calliantha Lundholm, Moestrup, & Hasle-have been identified as producers of DA in the Adriatic Sea. By means of enzme-linked immunosorbent assay (ELISA), high-performance liquid chromatography with UV and visible spectrum detection (HPLC-UV/VIS), and liquid chromatography with tandem mass spectrometry (LC-MS/MS), we reconfirmed the presence of DA in P. multistriata and P. delicatissima and detect for the first time in the Adriatic Sea DA in P. galaxiae Lundholm, & Moestrup. Furthermore, we attempted to answer the question of the distribution of DA production among Pseudo-nitzschia species and strains by sequencing the internal transcribed spacer (ITS) phylogenetic marker and the dabA DA biosynthesis gene and coupling this with toxicity data. Results show that all subclades of the Pseudo-nitzschia genus contain toxic species and that toxicity appears to be strain dependent, often with geographic partitioning. Amplification of dabA was successful only in toxic strains of P. multistriata and the presence of the genetic architecture for DA production in non-toxic strains was thus not confirmed.