Multiple stressor effects of predation by rotifers and herbicide pollution on different Chlamydomonas strains and potential impacts on population dynamics

Storage and Algal Association of Bacteria That Protect Microchloropsis salina from Grazing by Brachionus plicatilis

Loss of algal production from the crashes of algal mass cultivation systems represents a significant barrier to the economic production of microalgal-based biofuels. Current strategies for crash prevention can be too costly to apply broadly as prophylaxis. Bacteria are ubiquitous in microalgal mass production cultures, however few studies investigate their role and possible significance in this particular environment. Previously, we demonstrated the success of selected protective bacterial communities to save Microchloropsis salina cultures from grazing by the rotifer Brachionus plicatilis. In the current study, these protective bacterial communities were further characterized by fractionation into rotifer-associated, algal-associated, and free-floating bacterial fractions. Small subunit ribosomal RNA amplicon sequencing was used to identify the bacterial genera present in each of the fractions. Here, we show that Marinobacter, Ruegeria, and Boseongicola in algae and rotifer fractions from rotifer-infected cultures likely play key roles in protecting algae from rotifers. Several other identified taxa likely play lesser roles in protective capability. The identification of bacterial community members demonstrating protective qualities will allow for the rational design of microbial communities grown in stable co-cultures with algal production strains in mass cultivation systems. Such a system would reduce the frequency of culture crashes and represent an essentially zero-cost form of algal crop protection.

Density-Dependent Metabolic Costs of Copper Exposure in a Coastal Copepod

Traditional ecotoxicology methods involving copepods have focused on exposure of pooled individuals and averaged responses, but there is increasing awareness of the importance of individual variation. Many biological traits are density dependent, and decisions to use single-individual or pooled exposure may affect responses to anthropogenic stressors. We investigated how conspecific density as a biotic stressor affects behavioral and respiratory responses to copper (Cu) exposure in the coastal copepod Tigriopus brevicornis. Adults were incubated at densities of 1, 2, or 4 individuals per replicate in 3.2 mL of exposure medium (23 µg Cu L^-1 or control). Our results show an interaction of Cu exposure and density on respiration. The Cu exposure increased respiration, but this effect diminished with increasing density. We also found reduced swimming activity with increasing density. We propose 2 nonexclusive alternative explanations for the density-dependent respiratory increase of Cu exposure: 1) a behavioral stress response to low conspecific density, or 2) increased Cu exposure due to increased swimming activity. We emphasize the importance of considering density-dependency in responses when designing and interpreting ecotoxicology studies. Environ Toxicol Chem 2021;40:2538-2546. © 2021 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Isolation of Four Microalgal Strains From the Lake Massaciuccoli: Screening of Common Pollutants Tolerance Pattern and Perspectives for Their Use in Biotechnological Applications

Aquatic ecosystems represent one of the largest reservoirs of phytoplankton accounting for most of the primary production of the Earth. The Lake Massaciuccoli located in Tuscany (Italy) is one of the largest swamps that in ancient times entirely covered the Versilia coastal plain. Despite its peculiar features, especially the eutrophic characteristics, its native microalgal consortia have never been explored up to now. In this work, we isolated and described four autochthonous microalgal strains from different sites in the lake (FB, Idr, CL_Sc, and CL_Ch); the four microalgal strains were identified within the Chlorella sorokiniana clade. We exposed them to ten of the most common or emerging environmental contaminants in order to describe their preliminary response to the tested substances: five metals (As, Fe, Ni, Cu, and Zn), two herbicides (Metolachlor and Sethoxydim), two antibiotics (Ciprofloxacin and Benzylpenicillin) and a non-steroidal anti-inflammatory drug (Ibuprofen). Physiological response of the strains highlighted intraspecific differences; strain CL_Sc was the most tolerant in presence of metals while strain Idr was the most sensitive. All strains were sensitive to sethoxydim and tolerant to metolachlor at all the tested concentrations. Strains FB and Idr were the most sensitive in presence of Ibuprofen while strain CL_Ch was the most sensitive to the highest Benzylpenicillin concentration. Resistance pattern of strain Idr somehow reflects both the phylogenetic and the geographic "isolation" from all other three strains. Finally, optical microscope observation confirmed some differences also in the microalgae morphological aspect. Overall, all the strains showed interesting responses in presence of high concentrations of the tested substances, representing putative interesting candidates for water remediation in wastewater treatment plants.

Overcoming the Biological Contamination in Microalgae and Cyanobacteria Mass Cultivations for Photosynthetic Biofuel Production

Microalgae and cyanobacteria have shown significant potential for the development of the next biofuels innovation because of their own characteristics as photosynthetic microorganisms. However, it is confronted with a lot of severe challenges on the economic scaling-up of the microalgae- and cyanobacteria-based biofuels production. One of these major challenges is the lack of a reliable preventing and controlling culture system of biological contamination, which can attack the cell growth or product accumulation causing crashing effects. To increase the commercial viability of microalgae- and cyanobacteria-based biofuels production, overcoming the biological contaminations should be at the top of the priority list. Here, we highlight the importance of two categories of biological contaminations and their controlling strategies in the mass cultivations of microalgae and cyanobacteria, and outline the directions that should be exploited in the future.

The Hidden Dimension: Context-Dependent Expression of Repeatable Behavior in Copepods

In ecotoxicology and aquatic ecology, we often ignore responses of individuals and focus on average responses. However, both terrestrial and aquatic animals display consistent behavioral differences between individuals. The distribution of behavioral differences within a population contains vital information for predicting population responses to novel environmental challenges. Currently, individual data for behavioral and physiological traits of small marine invertebrates are few, partly because such variation is lost within published group means and assumed normality. We tested the combined effects of an inorganic contaminant (copper) and a biological stressor (i.e., chemical cues of a fish predator) on activity in a marine copepod. Although direct stress effects were weak, individuals behaved consistently differently, depending on the context. Individual differences in behavior were only expressed under the influence of kairomones, but not by copper exposure alone. This finding indicates that copepods express repeatable and context-dependent behavior. We also demonstrate how large variations in behavioral data can hide consistent differences between individuals. Environ Toxicol Chem 2020;39:1017-1026. © 2020 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals, Inc. on behalf of SETAC.

Biological contamination and its chemical control in microalgal mass cultures

Microalgae are versatile sources of bioproducts, a solution for many environmental problems. However, and despite its importance, one of the main problems in large-scale cultures-the presence of contaminants-is rarely systematically approached. Contamination, or the presence of undesirable organisms in a culture, is deleterious for the culture and frequently leads to culture crashes. To avoid contamination, closed systems can be used; however, for very large-scale open systems, contamination is unavoidable and remediation procedures are necessary-ranging from physicochemical treatment to addition of biocidal substances. In all cases, early detection and culture monitoring are paramount. This article describes the biological contaminants, contamination mechanisms, and control systems used in open and closed cultures, discussing the latest advances and techniques in the area. It also discusses the complex interactions of algae with other microorganisms that can be expected in cultivation systems.

An affordable and automated imaging approach to acquire highly resolved individual data-an example of copepod growth in response to multiple stressors

Individual trait variation is essential for populations to cope with multiple stressors and continuously changing environments. The immense number of possible stressor combinations and the influence of phenotypic variation makes experimental testing for effects on organisms challenging. The acquisition of such data requires many replicates and is notoriously laborious. It is further complicated when responses occur over short time periods. To overcome such challenges, we developed an automated imaging platform to acquire temporally highly resolved individual data. We tested this platform by exposing copepods to a combination of a biotic stressor (predator cues) and a toxicant (copper) and measured the growth response of individual copepods. We tested the automatically acquired data against published manually acquired data with much lower temporal resolution. We find the same general potentiating effects of predator cues on the adverse effects of copper, and the influence of an individual’s clutch identity on its ability to resist stress, between the data obtained from low and high temporal resolution. However, when using the high temporal resolution, we also uncovered effects of clutch ID on the timing and duration of stage transitions, which highlights the importance of considering phenotypic variation in ecotoxicological testing. Phenotypic variation is usually not acknowledged in ecotoxicological testing. Our approach is scalable, affordable, and adjustable to accommodate both aquatic and terrestrial organisms, and a wide range of visually detectable endpoints. We discuss future extensions that would further widen its applicability.

Predation Risk Potentiates Toxicity of a Common Metal Contaminant in a Coastal Copepod

To examine whether natural stressors like predation risk affect responses to anthropogenic contaminants, we exposed nauplii of the copepod Tigriopus brevicornis to chemical cues from fish (kairomones) and copper (Cu). We tested effects of these treatments, singly and combined, on copepod age and size at maturity, and development stage sensitivity, while controlling for effects of genetic heterogeneity (clutch identity). Predation risk, Cu and clutch identity interacted in their effect on development time. Predation risk alone had minor effects, but potentiated Cu toxicity in the combined treatment by doubling the delay in age at maturity, as compared to Cu exposure alone. This potentiating effect on developmental delay appeared already at the first copepodite stage. The specific strength of response varied among nauplii from different females' clutches. There were no differences in copepod size at maturity among treatments. We did, however, find an interaction between the effect of Cu and clutch identity on copepod growth. Our results demonstrate the importance of ecological interactions for potentiating the toxicity of environmental contaminants. We also demonstrate the need to consider genetic heterogeneity in ecotoxicology. Natural variation in stressor responses has implications for the interpretation of results from toxicological studies using single-clone or inbred culture populations.

Removal and Biodegradation of 17β-Estradiol and Diethylstilbestrol by the Freshwater Microalgae Raphidocelis subcapitata

Natural steroidal and synthetic non-steroidal estrogens such as 17β-estradiol (E2) and diethylstilbestrol (DES) have been found in natural water, which can potentially endanger public health and aquatic ecosystems. The removal and biodegradation of E2 and DES by Raphidocelis subcapitata were studied in bacteria-free cultures exposed to single and mixture treatments at different concentrations for 96 h. The results showed that R. subcapitata exhibited a rapid and strong ability to remove E2 and DES in both single and mixture treatments by biodegradation. At the end of 96 h, the removal percentage of single E2 and DES achieved 82.0%, 80.4%, 74.6% and 89.9%, 73.4%, 54.1% in 0.1, 0.5, and 1.5 mg·L^-1, respectively. With the exception of the 0.1 mg·L^-1 treatment at 96 h, the removal capacity of E2 was more efficient than that of DES by R. subcapitata. Furthermore, the removal percentage of mixture E2 and DES achieved 88.5%, 82.9%, 84.3% and 87.2%, 71.8%, 51.1% in 0.1, 0.5, and 1.5 mg·L^-1, respectively. The removal percentage of mixed E2 was significantly higher than that of the single E2. The presence of DES could accelerate the removal of E2 from the mixture treatments in equal concentrations. In addition, the removal was mainly attributed to the biodegradation or biotransformation process by the microalgae cells rather than simple sorption and accumulation in the cells. The microalgae R. subcapitata demonstrated a high capability for the removal of the E2 and DES indicating future prospects for its application.

Acclimation of Chlamydomonas reinhardtii to ultraviolet radiation and its impact on chemical toxicity

The toxicity of chemical pollutants can be modulated under stressful environmental conditions, such as increased temperature, salinity or ultraviolet radiation (UVR), due to the interaction of effects during simultaneous stressor exposure. However, organisms may acclimate to such conditions by activation of physiological and biochemical defence mechanisms. In sequential exposures, organisms acclimated to environmental stressors may display an increased sensitivity or co-tolerance towards chemical pollutants. It has been suggested that co-tolerance might be expected for similarly acting stressors due to common defence mechanisms. To test this for combinations of UVR and chemical stressors, we first acclimatized the model green alga Chlamydomonas reinhardtii to UVR and subsequently compared the sensitivity of UVR pre-exposed and control algae towards chemicals. Selected chemicals all act on photosynthesis and thus share a common physiological target, but display distinct toxicity mechanisms. Results showed that UVR pre-exposure for four days partially inhibited algal growth and photosynthesis, but also increased algal tolerance to higher UVR levels, confirming UVR acclimation. HPLC analysis of algal pigments indicated that UVR acclimation might in part be explained by the protective function of lutein while the contribution of UVR absorbing compounds was less clear. Challenge exposure to chemicals in the absence of UVR showed that acclimated algae were co-tolerant to the photosensitizer rose bengal, but not to the herbicides paraquat and diuron, suggesting that the fast physiological and biochemical defence mechanisms that conferred tolerance of algae towards higher UVR levels were related to singlet oxygen defence. The presented study suggests that knowledge of the molecular toxicity mechanisms of chemicals, rather than their general physiological target, is needed in order to predict co-tolerance between environmental and chemical stressors.

Multiple stressor effects in Chlamydomonas reinhardtii--toward understanding mechanisms of interaction between effects of ultraviolet radiation and chemical pollutants

The effects of chemical pollutants and environmental stressors, such as ultraviolet radiation (UVR), can interact when organisms are simultaneously exposed, resulting in higher (synergistic) or lower (antagonistic) multiple stressor effects than expected based on the effects of single stressors. Current understanding of interactive effects is limited due to a lack of mechanism-based multiple stressor studies. It has been hypothesized that effect interactions may generally occur if chemical and non-chemical stressors cause similar physiological effects in the organism. To test this hypothesis, we exposed the model green alga Chlamydomonas reinhardtii to combinations of UVR and single chemicals displaying modes of action (MOA) similar or dissimilar to the impact of UVR on photosynthesis. Stressor interactions were analyzed based on the independent action model. Effect interactions were found to depend on the MOA of the chemicals, and also on their concentrations, the exposure time and the measured endpoint. Indeed, only chemicals assumed to cause effects on photosynthesis similar to UVR showed interactions with UVR on photosynthetic yield: synergistic in case of Cd(II) and paraquat and antagonistic in case of diuron. No interaction on photosynthesis was observed for S-metolachlor, which acts dissimilarly to UVR. However, combined effects of S-metolachlor and UVR on algal reproduction were synergistic, highlighting the importance of considering additional MOA of UVR. Possible mechanisms of stressor effect interactions are discussed.

Efficacy of binary combinations of botanical pesticides for rotifer elimination in microalgal cultivation

Binary interactions of celangulin, matrine and toosendanin against the rotifer Brachionus plicatilis were studied. Types of interactions (antagonism, synergism and addition) were dependent on the biocides themselves and their ratios in combinations. Mixtures of matrine/toosendanin mainly produced addition owing to their similar modes of action aiming at the nervous system. Combinations of celangulin mixed with matrine or toosendanin at 1:9 exhibited synergism, which is attributed to the interference of matrine or toosendanin with the detoxification enzymes of celangulin. Both the synergistic combinations were inappropriate for rotifer extermination in Isochrysis sp. cultivation owing to the high phytotoxicity resulting from the absence of cell walls. However, the celangulin/toosendanin (1:9) mixture decreased rotifer reproduction without damaging cells of Chlorella and Nannochloropsis sp. Application of frequent, low doses of celangulin/toosendanin (1:9) mixture also reduced the dosage of biocides, thereby reducing the cost of exterminating rotifers, and indicating a considerable practical application in microalgal cultivation.

Brief communication: the ecosystem perspective in ecotoxicology as a way forward for the ecological risk assessment of chemicals

One of the objectives of the European Union (EU) ecological risk assessment of chemicals (ERA) is to derive maximum environmental concentrations that are not expected to cause adverse ecological effects. To this end, related EU directives list protection goals as well as guidelines that should be used to reach these goals. It is generally accepted that the individual-level endpoints on which these guidelines are based do not correspond to the listed population- and ecosystem-level protection goals. In this article, we identify 5 research topics that are key to bridging this gap: 1) the refinement of population-level effects and recovery rates by explicitly taking into account competition and 2) predation, 3) the assessment of chemical effects on biodiversity, 4) the assessment of chemical stress on ecosystem functions and services, and 5) the quantification of the effects of chemical mixtures. In addition, we illustrate why an ecosystem perspective is needed to address these topics and to inform the risk assessment process. We propose the use of existing ecotoxicological community, food web, and ecosystem models to tackle these issues and discuss why new models are needed to predict chemical effects on biodiversity.

The toxicity of chemical pollutants in dynamic natural systems: the challenge of integrating environmental factors and biological complexity

The dynamics of abiotic and biotic environmental factors, like temperature and predation, can strongly influence the effects of anthropogenic chemical pollutants in natural systems. Responses to toxicants and their interactions with environmental factors can occur at varying temporal scales and at different levels of biological complexity (from cells to organisms, populations, communities and ecosystems). Environmental factors may affect tolerance to toxic pollutants under non-stressful conditions, and cause adverse multiple stressor effects under stressful conditions. Adaptive processes, however, have the potential to either mitigate (by co-tolerance) or increase (due to associated costs) the sensitivity of individuals, populations, and communities to pollutants through selection and evolution of traits (at the individual and population levels) and changes in species composition (at the community level). Responses to such multiple stressor effects on different biological levels and temporal scales are not considered in current risk assessment practices. We suggest that these effects should and can be addressed by: (i) designing ecotoxicological experiments with temporal exposure patterns that accommodate adaptive processes, (ii) using trait-based approaches to assess biological responses and natural selection in an integrated manner, and (iii) using energy allocation models to link responses at different levels of biological organization.