Cyanotoxins are a significant concern due to their frequent presence in Southamerica waters. While numerous studies have investigated the toxic effects of MC-LR, knowledge regarding the toxicity of [D-Leu1]MC-LR remains limited. The aim of this study was to determine the impact of [D-Leu1]MC-LR and MC-LR administration on different brain structures in rats and the resulting modifications in oxidative stress. Male Sprague-Dawley rats were divided into two groups and administered 5 intraperitoneal injections of mixed MCs at doses of 2 and 15 µg kg-1 for each injection over a 21-day period, i.e. total doses of 10 and 75 µg kg-1.The MCs consisted on MC-LR (3 %), [D-Leu1]MC-LR (96.7 %) and others (0.3 %) isoforms. To evaluate the effect of treatments with different doses, the concentration of both MC isoforms, reactive oxygen species (ROS), lipid damage and antioxidant activity were measured in the cerebral cortex, hippocampus, striatum and cerebellum. The results revealed variability in MC concentration across brain regions. The accumulation rate of MC-LR was 2000 times higher than that of [D-Leu1]MC-LR, regardless of the dose administered at different areas. Taken together, our results highlighted that chronic exposure to MCs induced a mild oxidative stress in the rat brain characterized by increased ROS and antioxidant defense activation due to [D-Leu1]MC-LR in both the striatum and cortex at high dose. At low dose, the uptake of only MC-LR was determined in the cerebellum and hippocampus, resulting in increased ROS levels but no change in CAT activity in the hippocampus. In contrast, in the cerebellum, there was a decrease in ROS, possibly due to increased CAT consumption. However, the absence of detection of an MC variant under certain conditions does not allow for the exclusion of its metabolic effects. Chronic MC administration resulted in dose- and region-dependent distribution within the rat brain. Reactive species levels and cellular responses also varied by dose and region.

Toxic cyanobacterial blooms, primarily caused by Microcystis aeruginosa, are increasing globally due to climate change. These harmful organisms have adapted to high temperature and UV radiation (UVR), posing a significant threat to drinking water. While UVBR can damage cyanobacteria, they may avoid it with antioxidant defense mechanisms. Microcystins (MCs), cyclic hepatotoxic heptapeptides produced by cyanobacteria, can harm aquatic and terrestrial organisms, but their role in antioxidant protection remains unclear. This study investigated the relationship between gene expression and MC content in Microcystis aeruginosa cells pre-adapted to elevated temperatures (29 °C) exposed to natural UVR for several days. We have demonstrated a strong resilience in M. aeruginosa to high doses of UVBR, largely attributed to its enhanced antioxidant capacity following pre-exposure to elevated temperatures, as confirmed by previous studies. Moreover, our findings suggest that MCs may act as scavengers as part of the UVR protection mechanisms. This is evidenced by a temporal lack of correlation between the abundance of mcy transcripts and the cellular toxin content, where toxin quotas were lower despite increased mcy transcription. These findings are particularly relevant to the ecophysiological role of MCs, suggesting its potential involvement in increased blooms of toxic M. aeruginosa under conditions of climate change and eutrophication. This information is crucial for effective water treatment planning.

Heat waves, are a major concern related to climate change, and are projected to increase in frequency and severity. This temperature rise causes thermal stratification, exposing surface-dwelling organisms to higher levels of ultraviolet radiation (UVR). This study aims to understand how the toxic bloom-forming cyanobacterium Microcystis aeruginosa adapts to changing climatic conditions. The effects of increased temperature and UVR were evaluated in terms of cell abundance, reactive oxygen and nitrogen species (ROS/RNS), the antioxidant activity of catalase (CAT), superoxide dismutase (SOD), glutathione S transferase (GST), fatty acid (FA) content, and lipid damage. Negative UVR effects on biomass, lipid damage, and polyunsaturated fatty acids (PUFAs) were more pronounced at 26 degrees C compared to 29 degrees C. However, antioxidant responses were higher at 29 degrees C. The relative abundance of omega 6 FAs was less affected by UVA, while omega 3 FAs were highly sensitive at 29 degrees C but unsaturated fatty acids (UFA) did not experience peroxidation. The differential response in FA to high temperature and UVR results in differences in lipid damage and antioxidants. Changes in membrane FA may suggest an adaptation strategy at high UVR conditions. The exposure to environmental changes can alter membrane fluidity, affecting cell physiology. Thus, to survive UVR exposure, M. aeruginosa maintains a balance between damage and stress adaptation, increasing the protection of selected PUFAs at high temperatures, allowing them to effectively cope with the harmful effects of elevated temperature and UVR.

Las cianobacterias son organismos fotosintéticos importantes para diversos ciclos vitales de la biósfera; sin embargo, algunos géneros como Microcystis tienen la capacidad de formar floraciones y producir cianotoxinas que comprometen la calidad del agua. Este estudio tuvo como objetivo validar el uso de PCR punto final para detectar cianobacterias, el género Microcystis y su capacidad genética para producir microcistinas. Se utilizaron tres pares de oligonucleótidos para obtener las secuencias de las regiones del gen 16S rRNA de cianobacterias y de Microcystis, así como del gen mcyA asociado con la producción de microcistinas. El uso de PCR de punto final permitió la detección específica de cianobacterias y Microcystis en concentraciones celulares hasta 10 veces por debajo del límite de alerta de florecimiento, así como la detección del gen mcyA, tanto en cepas aisladas como en una comunidad microbiana simulada. La eficacia del uso de PCR de punto final para la detección específica de cianobacterias lo convierte en una herramienta de monitoreo temprano, capaz de predecir la producción potencial de microcistinas y, por tanto, resaltar su utilidad para la gestión de la calidad del agua para consumo humano.

Temperature up-shift and UV-A radiation effects on growth, lipid damage, fatty acid (FA) composition and expression of desaturase genes desA and desB were investigated in the cyanobacteria Microcystis aeruginosa. Although UV-A damaging effect has been well documented, reports on the interactive effects of UV radiation exposure and warming on cyanobacteria are scarce. Temperature and UV-A doses were selected based on the physiological responses previously obtained by studies with the same M. aeruginosa strain used in this study. Cells pre-grown at 26 °C were incubated at the same temperature or 29 °C and exposed to UV-A + PAR and only PAR for 9 days. Growth rate was significantly affected by UV-A radiation independently of the temperature throughout the experiment. High temperature produced lipid damage significantly higher throughout the experiment, decreasing at day 9 as compared to 26 °C. In addition, the cells grown at 29 °C under UV-A displayed a decrease in polyunsaturated FA (PUFA) levels, with ω3 PUFA being mostly affected at the end of exposure. Previously, we reported that UV-A-induced lipid damage affects differentially ω3 and ω6 PUFAs. We report that UV-A radiation leads to an upregulation of desA, possibly due to lipid damage. In addition, the temperature up-shift upregulates desA and desB regardless of the radiation. The lack of lipid damage for UV-A on ω3 could explain the lack of transcription induction of desB. The significant ω6 decrease at 26 °C in cells exposed to UV-A could be due to the lack of upregulation of desA.

The Western Antarctic Peninsula (WAP) experiences one of the highest rates of sea surface warming globally, leading to potential changes in biological communities. Long-term phytoplankton monitoring in Potter Cove (PC, King George Island, South Shetlands) from the 1990s to 2009 revealed consistently low biomass values, and sporadic blooms dominated by cold-water microplankton diatoms. However, a significant change occurred between 2010 and 2020, marked by a notable increase in intense phytoplankton blooms in the region. During this period, the presence of a nanoplankton diatom, Shionodiscus gaarderae, was documented for the first time. In some instances, this species even dominated the blooms. S. gaarderae is recognized for producing blooms in temperate waters in both hemispheres. However, its blooming in the northern Southern Ocean may suggest either a recent introduction or a range shift associated with rising temperatures in the WAP, a phenomenon previously observed in experimental studies. The presence of S. gaarderae could be viewed as a warning sign of significant changes already underway in the northern WAP plankton communities. This includes the potential replacement of microplankton diatoms by smaller nanoplankton species. This study, based on observations along the past decade, and compared to the previous 20 years, could have far-reaching implications for the structure of the Antarctic food web.

In the austral summer of 2020, record high temperatures were registered in the Western Antarctic Peninsula. This offered a unique opportunity to evaluate the effect of extreme sea surface temperature and natural heatwaves on the metabolic balance (i.e. the balance between production and respiration), lipid damage and the possible change in lipid composition of coastal Antarctic (Potter Cove, King George/25 de Mayo Island, South Shetlands) microbial communities. Two marine heatwaves, one in January and a second one in February 2020 showed mean temperatures of 1.8 °C above the 20-year climatology values. During the first heatwave, a rapid and strong (60%) decrease in microbial community biomass was observed, Criptophyceae were replaced by unidentified nanophytoflagellates and other heterotrophic groups. The community experienced an increase in heterotrophic metabolism via an increase in community respiration (CR, 12.79 mmolO2 m−3d−1) and a negative net community production (NCP, −14.9 ± 0.31 mmolO2 m−3d−1), leading to a production:respiration (P:R) rate < 1. Additionally, the most representative fatty acids (FAs: 14:0, 16:0, 18:0, 16:1ω9, 18:1ω9, 18:2ω6 and 18:3ω3) decreased, except for the monounsaturated FAs (MUFA) 16:1ω9 and 18:1 ω9, which increased during this first heatwave. In the second marine heatwave, total biomass dropped to the minimum values reported during the entire study. Here, CR was at its maximum (25.09 mmolO2 m−3d−1), but NCP was also positive (1.96 mmolO2 m−3d−1) and P:R > 1, associated with an active autotrophic community. Again, significant lipid damage, a decrease in saturated FAs and ⍵6 polyunsaturated FAs, and an increase in MUFAs occurred. This field study validates previous experimental results on changes in natural plankton composition and physiology under global warming scenarios.

The Beagle Channel at the southernmost tip of South America is an interoceanic passage connecting the Pacific and the Atlantic Oceans. It is characterized by intricate coastlines and changing bathymetry, a dominant West to East circulation pattern, and a strong longitudinal gradient of glacial fresh-water discharge. Harmful algal blooms (HAB) and toxic outbreaks have been detected along the channel for the last two decades and monitored by both Chilean and Argentinean agencies. This unique scenario was used to try to answer whether HABs propagate from West to East along the channel following the main water flow, so that a sequential, spatial pattern can be identified, or if local dynamics due to particular hydrographic characteristics might favor HAB formation in different areas along the channel. For this analysis, we selected data from three austral spring-summer seasons, 2009–2010, 2010–2011, and 2012–2013, when by means of the mouse bioassay important concentrations of saxitoxins (STX) derivatives were detected in shellfish from different stations along the channel. Relevant information on hydrographical (temperature, salinity, bathymetry, main currents), chemical (macronutrients), and biological (cell abundance of the main species responsible for the toxic outbreaks in the channel, i.e. Alexandrium catenella) characteristics are analyzed. Results show that during the years when toxicity was highest, there was no evidence of West to East (longitudinal) transport of toxins along the channel. Contrastingly, smaller-scale patterns could explain the observed dynamics associated with three sub-basins previously described for the Beagle Channel, identified as western, central, and eastern regions. We built a conceptual model based on own and published data on bathymetry, PAR, salinity, water residence time, silicate availability, and DOM to understand the differences in HAB presence among the sub-basins, which allows explaining the higher toxicity values registered in the central part of the channel as compared to the western or easternmost regions.

Exposure to constant light or darkness for long periods has diverse effects on circadian physiology. Iron (Fe) overloading promotes oxidative stress and causes alterations in cellular structure and function in animals and humans. The aim of this study is to evaluate the interactions among serum melatonin (ML), photoperiod manipulation, and Fe overloading in rats. The results showed that constant darkness exposure for 15 days significantly increased serum ML levels (up to 22%) while the constant light exposure failed to reduce the serum ML level compared to the normal light/dark cycle treated rats. The lost serum ML level usually from the pineal gland under the long term of constant light exposure may be compensated by ML generated by other organs which adapted to the situation. Also, Fe overloading decreased ML production due to this molecule being consumed to scavenge the free radicals induced by the Fe overloading. In addition, we observed interactions among constant light or darkness exposure, Fe overloading and serum ML level. Overall, our results support the hypothesis of ML as scavenging molecule; it may be an effective therapeutic tool in iron-induced oxidative stress.

Cyanobacteria have different defence mechanisms, which have improved over time, to avoid or mitigate oxidative stress by using antioxidants as reactive species scavengers. The objective of the present study was to evaluate the effects of increased temperature, over several days of exposure, on biomass, lipid damage, oxygen and nitrogen reactive species, and different antioxidants on Microcystis aeruginosa (harmful cyanobacteria). Unicellular cultures were exposed to elevated (29 degrees C) and control (26 degrees C) temperatures for 10 d. The temperature shift induced activation of enzymatic antioxidant system and changes in content of non-enzymatic antioxidants after 2 d of exposure to 29 degrees C. This was responsible for a lower content of reactive species during the subsequent days. An increase in enzymatic antioxidant activity, depending on the exposure time, was observed. In addition, there was a differential non-enzymatic antioxidant response that was also time dependent, which could be important to counteract oxidative stress induced by increases in temperature. Overall, the initial increase in beta carotene and astaxanthin content followed by an increased activity of catalase together with superoxide dismutase and glutathione S transferase activities allowed the cyanobacteria to counteract the oxidative stress induced, and improved their growth at the increased temperature. Our results increase the understanding of different antioxidant responses, integrating enzymatic and non-enzymatic protection mechanisms over time when exposing M. aeruginosa to heatwaves. The survival capacity of Cyanobacteria in drinking water supplies can have serious implications for the environment and human health.

Toxigenic algal blooms have been reported since 1886 in the Beagle Channel, at the southern limit of South America, mainly associated with the occurrence of paralytic shellfish poisoning (PSP) toxins produced by dinoflagellates of the genus Alexandrium. Toxic outbreaks have serious impacts on marine wildlife and ecosystem services, particularly on fisheries and mussel aquaculture. Within the framework of the Shellfish Toxicity Monitoring Program carried out close to Almanza in Beagle Channel eastern coastal waters, here we analyzed the spatiotemporal patterns of PSP toxins in the Magellan mussel Aulacomya ater and the blue mussel Mytilus edulis, measured by the mouse bioassay for 12 years, between 2005 and 2017. PSP outbreaks occurred mostly during summer and their duration was significantly longer than for outbreaks detected during spring and winter. A marked interannual variability in their magnitude was also evident. The largest outbreaks were detected in summers 2010–2011, in extreme warm and low-wind conditions, reaching up to 5600 µg saxitoxin equivalent per 100 g of tissue, causing a closure of shellfish fisheries of up to 200 days. Small scale spatial variability in PSP was also found, the highest values being observed in the main mussel culture areas, and the lowest in the natural mussel beds. PSP toxicities for the Magellan mussel were significantly higher than for the blue mussel. Natural detoxification in mussels from Beagle Channel followed an exponential decay, with mean detoxification rates of 3.5% toxin day−1, lower than those from elsewhere in the world for similar PSP toxin concentrations, which means a longer time to attain concentration limits safe for human consumption. Understanding PSP dynamics is important to avoid large economic losses related to halting mussel production.

Among the bloom-forming cyanobacteria, Microcystis aeruginosa is one of the most harmful species [...].

The coastal Atlantic area of Patagonia has a marked variability in physicochemical and biological properties. It is already affected by global change, as evidenced in historical patterns of environmental drivers and in direct anthropogenic influences. Here we focus on the effects of global change on plankton, mostly on phytoplankton, which constitute the base of this highly productive ecosystem. The short-term impacts range from an inhibition of primary productivity, with solar ultraviolet radiation (UVR) as the dominant driver, to an enhancement mainly caused by increased inputs of nutrients. Most studies evaluated the individual responses of bacterio-, phyto-, and meroplankton to solar UVR, while a few others have assessed the spatial distribution of zooplankton in relation to anthropogenic influence. Long-term effects of global change drivers (e.g., antagonistic or synergistic) include taxonomic changes of the communities toward those dominated by potential mixo−/heterotrophic nanoflagellates, which may alter the atmosphere-sea exchange and the sequestration of CO2. The interaction of phytoplankton – heterotrophs – can affect the overall response to the global change of plankton food webs mainly by cascading effects, and very few studies have considered trophic interactions. Multi-trophic experiments are needed to improve our understanding of the impact of global change on the coastal plankton of Patagonia.

Under the present changing climate conditions and the observed temperature increase, it is of high importance to understand its effects on aquatic microbial life, and organisms' adaptations at the biochemical level. To adjust to temperature or salinity stress and avoid cell damage, organisms alter their degree of fatty acids (FAs) saturation. Thus, temperature is expected to have strong effects on both the quantity and quality of FAs in aquatic microorganisms. Here we review some recent findings about FAs sensitivity to climate change in contrasting environments. Overall, heat waves may induce changes in the relative abundance of polyunsaturated FAs (PUFA). However, the impact of the exposure to warming waters is different in temperate and polar environments. In cold marine waters, high concentration of omega-3 (ω3) FAs such as eicosapentaenoic acid (EPA) is promoted due to the activation of the desaturase enzyme. In this way, cells have enough energy to produce or activate antioxidant protection mechanisms and avoid oxidative stress due to heat waves. Contrastingly, under high irradiance and heat wave conditions in temperate environments, photosystems' protection is achieved by decreasing EPA concentration due to desaturase sensitivity. Essential FAs are transferred in aquatic food webs. Therefore, any alteration in the production of essential FAs by phytoplankton (the main source of ω3) due to climate warming can be transferred to higher trophic levels, with cascading effects for the entire aquatic ecosystem.

Marine phytoplankton can utilize different strategies to cope with ocean warming and freshening from glacial melting in polar regions, which are disproportionally impacted by global warming. In the present study, we investigated the individual and combined effects of a 4 °C increase in seawater temperature (T+) and a 4 psu decrease in salinity (S−) from ambient values on biomass, nutrient use, fatty acid composition and lipid damage biochemistry of natural phytoplankton assemblages from Potter Cove (25 de Mayo/King George Island, Antarctica). Experiments were conducted by exposing the assemblages to four treatments during a 7-day incubation period using microcosm located along shore from January 23 to 31, 2016. The N:P ratio decreased in all treatments from day 4 onwards, but especially under high temperature (T+). Lipid damage was mainly detected under S0T+ and S−T+ conditions, and it decreased when the production of the antioxidant α-tocopherol increased. This antioxidant protection resulted in a build-up of phytoplankton biomass, especially at T+. Under the combined effect of both stressors (S−T+), the concentration of ω3 fatty acids increased, potentially leading to higher-quality FA composition. These results, which were related to the dominance of sub-Antarctic species in phytoplankton assemblages, contribute to the understanding of the potential consequences of ocean warming and increase seawater freshening on the trophic webs of the Southern Ocean.

A correction to this paper has been published: https://doi.org/10.1007/s00300-021-02834-3

The success of Limnoperna fortunei as an invasive freshwater bivalve species is related to its physiological plasticity to endure changes in environmental conditions. The aim of this study was to investigate the physiological responses of L. fortunei after feeding on Microcystis aeruginosa grown at 26 °C (control) and 29 °C during 10 days. At the beginning, we measured biomass, fatty acids (FAs) composition on Cyanobacteria grown at both temperatures at different time intervals. Afterwards, mussels were fed with the thawed M. aeruginosa cells and their FA profile was measured after 15 days of feeding. M. aeruginosa exposed to 29 °C had the highest content of the FAs 18:2ω6 and cis-18:1ω9. The FA profile of the consumer L. fortunei fed with M. aeruginosa cultures grown at 29 °C was also significantly different to those fed with cultures grown at 26 °C, with a significant increased Eicosapentaenoic acid (EPA, 20:5ω3) and Arachidonic acid (ARA, 20:4ω6) concentrations. L. fortunei was already known to be physiologically adapted to live at 29 °C, but our results also shown a high biosynthesis of EPA and ARA (increase of 70 and 40% respectively, compared with 26 °C) and avoided the lipid peroxidation of both FAs. This increased EPA and ARA biosynthesis may be an important source of ω3 and ω6 polyunsaturated FAs (PUFAs) for higher trophic levels, such as the pelagic fishes or birds that mainly prey on these mussels. The transfer of the cyanobacterial response at higher temperature to higher trophic levels will influence the overall functioning of freshwater bodies.

Changes in fatty acid (FA) composition can mean a mechanism of acclimation of Cyanobacteria to climate change. The objective of the present study was to evaluate the effects of increased temperature on M. aeruginosa cultures in terms of FA content, lipid damage, biomass and reactive oxygen species (ROS). Unicellular cultures were exposed to high (29 degrees C) and control (26 degrees C) temperature for 12 days. Differential sensitivity of omega 3 FAs was observed after 2 days of exposure to elevated temperature (29 degrees C). Also, no significant differences in ROS content at different temperatures were observed although there was a significant decrease compared to the value at the start of the incubation. Thus, low FA peroxidation of selected omega 6 PUFAs and potentially increased activation of antioxidant systems, resulting in lower lipid damage (on average 35%), could explain the strong acclimation to high temperature as shown by the increased growth rate (11%) compared to the control conditions. In high temperature conditions we found a retarded desaturation to 18:3 omega 3 and 18:4 omega 3 PUFAs which were 40% lower compared with control at the end of incubation. Overall, growth rate and omega-6 FA were increased at high temperature as a mechanism of successful acclimation. This is highly relevant for the ecological role of M. aeruginosa as food source for grazers. A reduced FA level can have serious implications for the flow of energy and thus the overall functioning of the ecosystem.

The climate around the Western Antarctic Peninsula (WAP) is rapidly changing and dramatically affecting marine coastal waters. Increases in air and seawater temperatures, not matter how small, can alter coastal biological communities due to both temperature increases as well as salinity reduction from glacier melting. The aim of this study was to evaluate the individual and combined effects of elevated sea surface temperature (+ 4 degrees C) and decreased salinity (-4) on growth and assemblage composition of natural summer phytoplankton from Potter Cove (King George Island, South Shetlands, northern WAP), using an outdoor microcosm experiment. Pigment composition was analyzed by high performance liquid chromatography (HPLC/Chemtax) and species composition by light and electron microscopy. Increases in phytoplankton biomass during the first 3 days at elevated-temperatures coincided with an increase in the abundance and the specific growth rate of small centric diatoms (Chaetoceros socialis and Shionodiscus gaarderae, mostly observed in temperate waters) and unidentified small phytoflagellates < 5 mu m. In contrast, pennate diatoms significantly decreased. At the end of the experiment on day 7, under nitrate and phosphate limitation, chlorophytes abundances increased under low salinity whereas prasinophytes decreased in all treatments. This study suggests that climate change could notably affect Antarctic phytoplankton composition by favouring temperate-water species previously undetected in Antarctic waters, such us S. gaarderae. Moreover, the observed changes in phytoplankton structure, associated with an increase of nano- over micro-size taxa, could have important implications for future Antarctic food webs.