This study investigated the effect of lipid extraction of microalgae feedstocks subjected to hydrothermal carbonization (HTC) with regard to the carbonization degree, chemical composition and phytotoxicity of hydrochars produced under different reaction temperatures and residence times. Special attention was given to the formation and composition of secondary char, as this part of the hydrochar may be of particular importance for environmental and technical applications. A microalgae polyculture grown in municipal wastewater was extracted to retrieve lipids, and both unextracted (MA) and extracted microalgae (EMA) were used to produce hydrochars at 180-240 degrees C for 1-4 h. The composition of the hydrochars was thoroughly characterized by elemental analysis, thermogravimetric analysis and pyrolysis-gas chromatography/mass spectrometry analysis. MA exhibited a greater carbonization degree than EMA and contained higher amounts of secondary char under the same processing conditions. During the carbonization of EMA, more decomposition products remained in the liquid phase and less polymerization occurred than for MA, which explained the lower solid yield of EMA-derived hydrochars in comparison to MA hydrochars. Consequently, although they contained potentially toxic substances (i.e., carboxylic acids, aldehydes and ketones), the EMA-derived hydrochars exhibited a lower phytotoxic potential. This indicates that low-temperature hydrochars containing less than 10% of extractives might be suitable as soil amendments, whereas extractive-rich hydrochars would be more appropriate for other long-term applications, such as adsorbents for contaminant removal, energy storage and composite materials. Detailed characterization of microalgae-derived hydrochars is required to enable the most suitable application areas to be identified for these materials, and thereby make full use of their function as carbon sinks.

NRPs were involved in growth responses of both cyanobacteria and algae; however, the primary driver of the growth trajectories was high pH induced by N. spumigena. Thus, the pH-mediated inhibition of eukaryotic phytoplankton may be involved in the bloom formation of N. spumigena. Nodularia spumigena is a bloom-forming cyanobacterium that produces several classes of nonribosomal peptides (NRPs) that are biologically active; however, the ecological roles of specific NRPs remain largely unknown. Here, we explored the involvement of NRPs produced by N. spumigena in interspecific interactions by coculturing the cyanobacterium and its algal competitors, the diatom Phaeodactylum tricornutum and the cryptomonad Rhodomonas salina, and measuring NRP levels and growth responses in all three species. Contrary to the expected growth suppression in the algae, it was N. spumigena that was adversely affected by the diatom, while the cryptomonad had no effect. Reciprocal effects of N. spumigena on the algae were manifested as the prolonged lag phase in R. salina and growth stimulation in P. tricornutum; however, these responses were largely attributed to elevated pH and not to specific NRPs. Nevertheless, the NRP levels in the cocultures were significantly higher than in the monocultures, with an up to 5-fold upregulation of cell-bound nodularins and exudation of nodularin and anabaenopeptin. Thus, chemically mediated interspecific interactions can promote NRP production and release by cyanobacteria, resulting in increased input of these compounds into the water. 

The increasing use of seaweeds in European cuisine led to cultivation initiatives funded by the European Union. Ulva lactuca, commonly known as sea lettuce, is a fast growing seaweed in the North Atlantic that chefs are bringing into the local cuisine. Here, different strains of Arctic U. lactuca were mass-cultivated under controlled conditions for up to 10 months. We quantified various chemical constituents associated with both health benefits (carbohydrates, protein, fatty acids, minerals) and health risks (heavy metals). Chemical analyses showed that long-term cultivation provided biomass of consistently high food quality and nutritional value. Concentrations of macroelements (C, N, P, Ca, Na, K, Mg) and micronutrients (Fe, Zn, Co, Mn, I) were sufficient to contribute to daily dietary mineral intake. Heavy metals (As, Cd, Hg and Pb) were found at low levels to pose health risk. The nutritional value of Ulva in terms of carbohydrates, protein and fatty acids is comparable to some selected fruits, vegetables, nuts and grains.

Nodularia spumigena is a bloom-forming diazotrophic cyanobacterium inhabiting brackish waters worldwide. This species produces non-ribosomal peptides (NRPs), including the hepatotoxin nodularin, often referred to as cyanotoxin. Several known classes of NRPs have various biological activities, although their modes of action are poorly understood. In the Baltic N. spumigena, there is a high NRP chemodiversity among strains, allowing their grouping in specific chemotypes and subgroups. Therefore, it is relevant to ask whether the NRP production is affected by intraspecific interactions between the co-existing strains. Using a novel approach that combines culture technique and liquid chromatography-tandem mass spectrometry for the NRP analysis, we examined N. spumigena strains under mono- and co-culture conditions. The test strains were selected to represent N. spumigena belonging to the same or different chemotype subgroups. In this setup, we observed physiological and metabolic responses in the test strains grown without cell contact. The changes in NRP levels to co-culture conditions were conserved within a chemotype subgroup but different between the subgroups. Our results suggest that intraspecific interactions may promote a chemical diversity in N. spumigena population, with higher NRP production compared to a single-strain population. Studying allelochemical signalling in this cyanobacterium is crucial for understanding toxicity mechanisms and plankton community interactions in the Baltic Sea and other aquatic systems experiencing regular blooms.

Active pharmaceutical ingredients (APIs) are vital to human health and welfare, but following therapeutic use, they may pose a potential ecological risk if discharged into the environment. Today's conventional municipal wastewater treatment plants are not designed to remove APIs specifically, and various techniques, preferably cost-effective and environmentally friendly, are being developed and evaluated. Microalgae-based treatment of wastewater is a sustainable and low-cost approach to remove nutrients and emerging contaminants. In this study, a North Sweden high-rate algal pond (HRAP) using municipal untreated wastewater as medium, was investigated in terms of API distribution and fate. Three six-day batches were prepared during 18 days and a total of 36 APIs were quantified within the HRAP of which 14 were removed from the aqueous phase above 50% and seven removed above 90% of their initial concentrations. Twelve APIs of a hydrophobic nature were mostly associated with the algal biomass that was harvested at the end of each batch. HRAPs treatment successfully removed 69% of studied APIs (25 of 36 studied) in six day time. The distribution of various APIs between the aqueous phase and biomass suggested that several removal mechanisms may occur, such as hydrophobicity driven removal, passive biosorption and active bioaccumulation.

Microalgal-based wastewater treatment and CO₂ sequestration from flue gases with subsequent biomass production represent a low-cost, eco-friendly, and effective procedure of removing nutrients and other pollutants from wastewater and assists in the decrease of greenhouse gas emissions. Thus, it supports a circular economy model. This is based on the ability of microalgae to utilise inorganic nutrients, mainly nitrogen and phosphorous, as well as organic and inorganic carbon, for their growth, and simultaneously reduce these substances in the water. However, the production of microalgae biomass under outdoor cultivation is dependent on several abiotic and biotic factors, which impact its profitability and sustainability. Thus, this study’s goal was to evaluate the factors affecting the production of microalgae biomass on pilot-scale open raceway ponds under Northern Sweden’s summer conditions with the help of a mathematical model. For this purpose, a microalgae consortium and a monoculture of Chlorella vulgaris were used to inoculate outdoor open raceway ponds. In line with the literature, higher biomass concentrations and nutrient removals were observed in ponds inoculated with the microalgae consortium. Our model, based on Droop’s concept of macronutrient quotas inside the cell, corresponded well to the experimental data and, thus, can successfully be applied to predict biomass production, nitrogen uptake and storage, and dissolved oxygen production in microalgae consortia.

The neurotoxins beta-N-methylamino-L-alanine (BMAA) and 2,4-diaminobutyric acid (DAB) are produced by cyanobacteria, diatoms and dinoflagellates and have been detected in seafood worldwide. Our present knowledge of their metabolism or biosynthesis is limited. In this study, the production of BMAA and DAB as a function of time was monitored in five strains representing four species of diatoms, i.e. Phaeodactylum tricornutum, Thalassiosira weissflogii, Thalassiosira pseudonana and Navicula pelliculosa, previously identified as BMAA and DAB producers. Subsequently, three strains were selected and exposed to three nitrogen treatments - starvation, control (the standard concentration in f/2 medium) and enrichment, because BMAA metabolism has been suggested to be closely associated with cellular nitrogen metabolism in both cyanobacteria and diatoms. Chlorophyll a and total protein concentrations were also determined. Our results indicate that BMAA and DAB production in diatoms is species- and strain-specific. However, production might also be affected by stress, particularly as related to nitrogen starvation and cell density. Furthermore, this study shows a significant correlation between the production of the two neurotoxins which might further suggest common steps in the metabolic pathways.

The native Ruditapes decussatus and the non-indigenous Ruditapes philippinarum are an important target of shellfish industries. The aim of this study was to compare an invader with a native species living in sympatry in the view of marine biotoxins accumulation. Samples were analysed for regulated and non regulated biotoxins. The consistently occurrence of okadaic acid-group toxins and BMAA, may cause human health problems and economical losses. A strong positive relationship was observed between species, with significantly higher DSP toxicity in R. decussatus. Similar toxin profiles dominated by DTX3 in both species suggests similar metabolic pathways. Lower DSP toxicity in R. philippinarum may favour their cultivation, but a tendency for higher levels of the non-regulated BMAA was observed, indicating risks for consumers that are not monitored. This study highlights the need to better understand the physiological responses and adaptations allowing similar species exposed to the same conditions to present different toxicity levels.

Maputo Bay is highly affected by large tidal changes and riverine freshwater input with a phytoplankton biomass peak during March each year. Microscopy analysis was used to describe how the phytoplankton community composition was affected by tidal changes, during four in situ incubation experiments. Using stable isotope tracers, new and total primary production, based on nitrate ((NO3-)-N-15)- and carbon (C-13-bicarbonate) assimilation were estimated. The highest biovolume of phytoplankton ( > 2 mu m) and also the highest C- and NO3--assimilation rates (nM h(-1)) were found at spring-high tide. The C:N (mol:mol) ratio of particulate organic matter (POM) varied between 6.0 and 8.2. The proportion of diatoms in the phytoplankton community was higher at spring-high tide as compared to neap-low tide, whereas dinoflagellates were found in a reverse pattern. New production ranged between 6.3% and 10.4% of total primary production and was thus within the range previously reported for tropical regions. The largest proportion of NO3- -based new production relative to total production was estimated during calm conditions and spring-high tide. Concordantly, a large fraction of the microplanktonic community covered their N-demand by other sources of N than NO3-.

beta-N-Methylamino-l-alanine (BMAA), a neurotoxin reportedly produced by cyanobacteria, diatoms and dinoflagellates, is proposed to be linked to the development of neurological diseases. BMAA has been found in aquatic and terrestrial ecosystems worldwide, both in its phytoplankton producers and in several invertebrate and vertebrate organisms that bioaccumulate it. LC-MS/MS is the most frequently used analytical technique in BMAA research due to its high selectivity, though consensus is lacking as to the best extraction method to apply. This study accordingly surveys the efficiency of three extraction methods regularly used in BMAA research to extract BMAA from cyanobacteria samples. The results obtained provide insights into possible reasons for the BMAA concentration discrepancies in previous publications. In addition and according to the method validation guidelines for analysing cyanotoxins, the TCA protein precipitation method, followed by AQC derivatization and LC-MS/MS analysis, is now validated for extracting protein-bound (after protein hydrolysis) and free BMAA from cyanobacteria matrix. BMAA biological variability was also tested through the extraction of diatom and cyanobacteria species, revealing a high variance in BMAA levels (0.0080-2.5797 mu g g(-1) DW).