Arsenic efflux from Microcystis aeruginosa under different phosphate regimes

Exploring phosphate impact on arsenate uptake and distribution in freshwater phytoplankton: Insights from single-cell ICP-MS

In this study, we investigated the interaction between arsenate (AsV) and phosphate (PO43-) in freshwater phytoplankton using single-cell inductively coupled plasma mass spectrometry (SC-ICP-MS). This study aimed to elucidate the influence of varying PO43- concentrations on arsenic (As) uptake and distribution at the single-cell level, providing insights into intraspecies diversity. Two species of freshwater phytoplanktons, Scenedesmus acutus and Pediastrum duplex, were cultured under different concentrations of PO43- and AsV in a controlled laboratory environment. Scenedesmus acutus, a species with strong salt tolerance, and Pediastrum duplex, known for its weak salt tolerance, were selected based on their contrasting behaviors in previous studies. SC-ICP-MS revealed non-uniform uptake of As by individual phytoplankton cells, with distinct variations in response to PO43- availability. Arsenic uptake by both species declined with a high PO43- level after 7 days of exposure. However, after 14 days, As uptake increased in S. acutus with higher PO43- concentrations, but decreased in P. duplex. Moreover, our findings revealed differences in cell morphology and membrane integrity between the two species in response to AsV and various PO43- concentrations. S. acutus maintained cell integrity under all experimental culture conditions, whereas P. duplex experienced cell lysis at elevated AsV and PO43- concentrations. This study highlights the varying responses of freshwater phytoplankton to changes in AsV and PO43- levels and underscores the advantages of SC-ICP-MS over conventional ICP-MS in providing detailed, cellular level insights. These findings are crucial for understanding and managing As pollution in aquatic ecosystems.

The influences of dissolved inorganic and organic phosphorus on arsenate toxicity in marine diatom Skeletonema costatum and dinoflagellate Amphidinium carterae

In this study, arsenate (As(V)) uptake, bioaccumulation, subcellular distribution and biotransformation were assessed in the marine diatom Skeletonema costatum and dinoflagellate Amphidinium carterae cultured in dissolved inorganic phosphorus (DIP) and dissolved organic phosphorus (DOP). The results of 3-days As(V) exposure showed that As(V) was more toxic in DOP cultures than in DIP counterparts. The higher As accumulation contributed to more severe As(V) toxicity. The 4-h As(V) uptake kinetics followed Michaelis-Menten kinetics. The maximum uptake rates were higher in DOP cultures than those in DIP counterparts. After P addition, the half-saturation constants remained constant in S. costatum (2.42-3.07 μM) but decreased in A. carterae (from 10.9 to 3.8 μM) compared with that in the respective P-depleted counterparts. During long-term As(V) exposure, A. carterae accumulated more As than S. costatum. Simultaneously, As(V) was reduced and transformed into organic As species in DIP-cultured S. costatum, which was severely inhibited in their DOP counterparts. Only As(V) reduction occurred in A. carterae. Overall, this study demonstrated species-specific effects of DOP on As(V) toxicity, and thus provide a new insight into the relationship between As contamination and eutrophication on the basis of marine microalgae.

Microcystis spp. and phosphorus in aquatic environments: A comprehensive review on their physiological and ecological interactions

Cyanobacterial blooms caused by eutrophication have become a major environmental problem in aquatic ecosystems worldwide over the last few decades. Phosphorus is a limiting nutrient that affects the growth of cyanobacteria and plays a role in dynamic changes in algal density and the formation of cyanobacterial blooms. Therefore, identifying the association between phosphorus sources and Microcystis, which is the most representative and harmful cyanobacteria, is essential for building an understanding of the ecological risks of cyanobacterial blooms. However, systematic reviews summarizing the relationships between Microcystis and phosphorus in aquatic environments are rare. Thus, this study provides a comprehensive overview of the physiological and ecological interactions between phosphorus sources and Microcystis in aquatic environments from the following perspectives: (i) the effects of phosphorus source and concentration on Microcystis growth, (ii) the impacts of phosphorus on the environmental behaviors of Microcystis, (iii) mechanisms of phosphorus-related metabolism in Microcystis, and (iv) role of Microcystis in the distribution of phosphorus sources within aquatic environments. In addition, relevant unsolved issues and essential future investigations (e.g., secondary ecological risks) have been highlighted and discussed. This review provides deeper insights into the relationship between phosphorus sources and Microcystis and can serve as a reference for the evaluation, monitoring, and effective control of cyanobacterial blooms.

Development of Chromatin Immunoprecipitation for the Analysis of Histone Modifications in Red Macroalga Neopyropia yezoensis (Rhodophyta)

Epigenetic regulation by histone modification can activate or repress transcription through changes in chromatin dynamics and regulates development and the response to environmental signals in both animals and plants. Chromatin immunoprecipitation (ChIP) is an indispensable tool to identify histones with specific post-translational modifications. The lack of a ChIP technique for macroalgae has hindered understanding of the role of histone modification in the expression of genes in this organism. In this study, a ChIP method with several modifications, based on existing protocols for plant cells, has been developed for the red macroalga, Neopyropia yezoensis, that consists of a heterogeneous alternation of macroscopic leaf-like gametophytes and microscopic filamentous sporophytes. ChIP method coupled with qPCR enables the identification of a histone mark in generation-specific genes from N. yezoensis. The results indicate that acetylation of histone H3 at lysine 9 in the 5' flanking and coding regions from generation-specific genes was maintained at relatively high levels, even in generation-repressed gene expression. The use of this ChIP method will contribute significantly to identify the epigenetic regulatory mechanisms through histone modifications that control a variety of biological processes in red macroalgae.

Effects of phosphate on the toxicity and bioaccumulation of arsenate in marine diatom Skeletonema costatum

The effects of nutrient phosphate (P) at environmentally relevant levels on the toxicity of arsenic (As) in marine microalgae have been rarely known. In the present study, we explored the toxicity and bioaccumulation of As in a globally distributed diatom species Skeletonema costatum at different ambient P concentrations. The results showed that As toxicity was suppressed at elevated P concentrations. Intracellular As content ([As]_intra) and the molar ratio of intracellular As to P ([As:P]) were negatively correlated with the ambient P concentrations. The trends of As bioaccumulation were substantially different between the relatively low (0, 0.5 and 1.5 μM) and high P concentrations (7.5 and 37.5 μM). Both [As]_intra and [As:P] suggested that As bioaccumulation was a better factor to explain the As toxicity comparing to the ambient As concentration. The 4 h As uptake kinetics at different P concentrations followed Michaelis-Menten kinetic pattern. The maximum uptake rates (V_max) decreased with the increase in P concentrations, and the half-saturation constants (K_d) remained constant except for that at extremely high P concentration (37.5 μM-P), suggesting the depression of P on As uptake was mainly due to the non-competitive effect. Overall, these results demonstrate that the P concentration in seawater is an important factor affecting As toxicity and bioaccumulation in the marine diatom. This study therefore helps us better understand the effects of eutrophication on the toxicity and biogeochemistry of As in the marine environment.

Phosphorus-arsenic interaction in the 'soil-plant-microbe' system and its influence on arsenic pollution

Elevated arsenic (As) in soil is of public concern due to the carcinogenicity. Phosphorus (P) strongly influences the adsorption, absorption, transport, and transformation of As in the soil and in organisms due to the similarity of the chemical properties of P and As. In soil, P, particularly inorganic P, can release soil-retained As (mostly arsenate) by competing for adsorption sites. In plant and microbial systems, P usually reduces As (mainly arsenate) uptake and affects As biotransformation by competing for As transporters. The intensity and pattern of PAs interaction are highly dependent on the forms of As and P, and strongly influenced by various biotic and abiotic factors. An understanding of the PAs interaction in 'soil-plant-microbe' systems is of great value to prevent soil As from entering the human food chain. Here, we review PAs interactions and the main influential factors in soil, plant, and microbial subsystems and their effects on the As release, absorption, transformation, and transport in the 'soil-plant-microbe' system. We also analyze the application potential of P fertilization as a control for As pollution and suggest the research directions that need to be followed in the future.

Organic Carbon transport model of abandoned river channels - A motif for floodplain geomorphology influencing biogeochemical swaying of arsenic

Meandering-river geomorphology, forming abandoned channels/lakes with organic carbon-burial and microbial reductive dissolution, play many crucial roles in controlling arsenic (As) fluxes in sinks such as contaminated aquifers of riverine alluvial plains across the world. Suhiya oxbow-lake in the middle alluvial plain of the River Ganga, was selected as the natural laboratory. A top-down multidisciplinary approach was chosen employing satellite imagery to analyse the annual oxbow-lake surface vegetation dynamics (Eichhornia and Hydrilla). Side-scan sonar profiles across two oxbow lakes along with River Ganga core data and vintage topographical maps, estimated the lake-sedimentation rate of 9.6 cm/yr. Organic carbon [amino acids, aromatics, lingo-phenols and lipids hydrocarbons] infiltration-based on hydrophobicity and molecular-mass was detected at different depths along the water and sedimentary column. Elemental analysis showed lake surface to groundwater the As conc. varied from (0.37 to 185 μg/l). A microbial diversity based study showed that large sized photoautotrophs Nostoc, Anabaena are replaced by Fe-oxido-reducing As-metabolizing bacteria e.g. Acidovorax, Dechloromonas and enteric organisms e.g. Enterobacter, Salmonella at bottom of water column. Based on these inferences, a conceptual organic carbon transport model was constructed to understand the preferential preservation and microbial diagenesis resulting in mobilization of As and other geogenic elements.

Arsenite Oxidation by Dunaliella salina is Affected by External Phosphate Concentration

Arsenic (As) contamination in terrestrial and aquatic environments is a well-known global environmental problem. The biooxidation of arsenite [As(III)] and subsequent arsenate [As(V)] removal have increasingly been used for remediation of As-polluted groundwater. However, little is known about As(III) oxidation by microalgae, especially those from saltwater environments. In this study, we investigated As(III) toxicity and oxidation in the marine microalga Dunaliella salina in the presence of different phosphate concentrations. The results of the As(III) toxicity experiments showed that D. salina was tolerant to As(III) (5.4 ± 0.31 mg As L^-1 at 72 h of culture). The As(V) percentage in the P-enriched (11.2 mg L^-1) medium was 7.2-fold greater than in the P-deficient one after 24-h exposure, indicating As(III) oxidation by D. salina was more pronounced with increased phosphate levels. Treatment of As(III) with and without 2,4-dinitrophenol (DNP) on the algal cells showed that As(III) oxidation occurred mainly on the cell surface and in the cytoplasm of D. salina. The results of this study suggest that transformation of As(III) into As(V) may be an important pathway of detoxification in D. salina and that phosphate plays a key role in this oxidation process.

Trophic-Level Interactive Effects of Phosphorus Availability on the Toxicities of Cadmium, Arsenic, and Their Binary Mixture in Media-Exposed Scenedesmus acutus and Media and Dietary-Exposed Daphnia pulex

Various anthropogenic activities simultaneously alter essential mineral nutrients and contaminant content in the environment. Depending on essential nutrient conditions, the uptake and effects of contaminants in exposed organisms may be altered. The addressing of ecological risk assessment (ERA) of contaminant mixtures has proven difficult. Furthermore, most assessments involving single contaminant exposures do not consider the interaction of essential nutrients on toxicological end points. Hypotheses for toxicological effects of cadmium (Cd), arsenic (As), and their binary mixture (Cd/As_mix) include alteration under varying dietary and media phosphorus (P) conditions. However, interactive effects and effect size (η²) are largely unknown. Here, we investigated the toxicities of Cd-, As-, and Cd/As_mix-treated media and diets on Scenedesmus acutus (a primary producer) and Daphnia pulex (a primary consumer), under varied media and dietary P conditions [low (LP), median (MP), and optimum (COMBO)]. Our results showed significant (p < 0.05) interactive effects and concentration dependent growth inhibition of S. acutus. The toxicity (at day 7) of Cd against S. acutus was 2×, 11×, and 4× that of As in LP, MP, and COMBO conditions, respectively, while the joint toxicity effects of Cd/As_mix were partially additive in LP and COMBO, and synergistic in MP media. Furthermore, acute lethal toxicity (96 h) of Cd in D. pulex was ∼60× that of As, while Cd/As_mix joint toxicity was synergistic. Chronic toxicity (14 d) in D. pulex showed significant (p < 0.05) interaction of As and P-availability on survival, reproduction, and behavior (distance moved, velocity, acceleration and mobility), while Cd and P availability showed significant interactive effect on rotational behavior. Dose response effects of Cd, As, and Cd/As_mix in S. acutus and D. pulex were either monophasic or biphasic under varying nutrient conditions. This study provides empirical evidence of the interactive effects of media/dietary P and toxic metals (Cd, As, and Cd/As_mix) at environmentally relevant concentrations, emphasizing the need for consideration of such interactions during ERA.

Interaction of graphene oxide with co-existing arsenite and arsenate: Adsorption, transformation and combined toxicity

The outstanding commercial application potential of graphene oxide (GO) will inevitably lead to its increasing release into the environment, and then affect the environmental behavior and toxicity of conventional pollutants. Interactions between arsenite [As (III)]/arsenate [As (V)] with GO and their combined toxicity to Chlorella pyrenoidosa were investigated. Under abiotic conditions, approximately 42% of the adsorbed As (III) was oxidized by GO with simulated sunlight illumination, which was induced by electron-hole pairs on the surface of GO. Co-exposure with GO greatly enhanced the toxicity of As (III, V) to alga. When adding 10 mg/L GO, the 72 h median effect concentration of As (III) and As (V) to C. pyrendoidosa decreased to 12.7 and 9.4 mg/L from 30.1 and 16.3 mg/L in the As alone treatment, respectively. One possible mechanism by which GO enhanced As toxicity could be that GO decreased the phosphate concentration in the algal medium, and then increased the accumulation of As (V) in algae. In addition, transmission electron microscope (TEM) images demonstrated that GO acted as a carrier for As (III) and As (V) transport into the algal cells. Also, GO induced severe oxidative stress, which could have subsequently compromised important detoxification pathways (e.g., As complexation with glutathione, As methylation, and intracellular As efflux) in the algal cells. Our findings highlight the significant impact of GO on the fate and toxicity of As in the aquatic environment.

Dissolved organic phosphorus enhances arsenate bioaccumulation and biotransformation in Microcystis aeruginosa

Only limited information is available on the effects of dissolved organic phosphorus (DOP) on arsenate (As(V)) bioaccumulation and biotransformation in organisms. In this study, we examined the influence of three different DOP forms (β-sodium glycerophosphate (βP), adenosine 5'-triphosphate (ATP), and D-Glucose-6-phosphate disodium (GP) salts) and inorganic phosphate (IP) on As(V) toxicity, accumulation, and biotransformation in Microcystis aeruginosa. Results showed that M. aeruginosa utilized the three DOP forms to sustain its growth. At a subcellular level, the higher phosphorus (P) distribution in metal-sensitive fractions (MSF) observed in the IP treatments could explain the comparatively lower toxic stress of algae compared to the DOP treatments. Meanwhile, the higher MSF distribution of arsenic (As) in M. aeruginosa in the presence of DOP could explain the higher toxicity with lower 96-h half maximal effective concentration (EC₅₀) values. Although we observed As(V) and P discrimination in M. aeruginosa under IP treatments with high intracellular P/As, we did not find this discrimination under the DOP treatments. As accumulation in algal cells was therefore greatly enhanced by DOP, especially βP, given its lower transformation rate to phosphate compared to ATP and GP in media. Additionally, As(V) reduction and, subsequently, As(III) methylation were greatly facilitated in M. aeruginosa by the presence of DOP, particularly GP, which was confirmed by the higher relative expression of its two functional genes (arsC and arsM). Our findings indicate that As(V) accumulation and its subsequent biotransformation were enhanced by organic P forms, which provides new insight into how DOP modulates As metabolism in algae.

Comparative biotransformation and detoxification potential of arsenic by three macroalgae species in seawater: Evidence from laboratory culture studies

Algae accumulate and metabolize arsenic (As) and facilitate cycling and speciation of As in seawater. The laboratory-controlled macroalgal cultures were exposed to different molar ratios of As(V) and phosphate (P) in seawater for evaluating the uptake and metabolism of As, as a function of As(V) detoxification through biotransformation. Chlorophyll fluorescence of algal species was not significantly affected by the culture conditions (p > 0.05). Addition of 10 μM P positively reduce As stress, but different As(V)/P ratios significantly affect the growth rate (p < 0.05). Algae readily accumulated As(V) after the inoculation, transformed intracellularly, and released gradually into the medium along the incubation period, depending on As(V)/P molar ratios. Reduction and methylation were the leading processes of As(V) metabolism by Pyropia yezoensis, whereas Sargassum patens showed only the reduction. Sargassum horneri reduced As(V) under low level (0.1 μM), but both reduction and methylation were observed under a high level (1 μM). At the end of incubation, 0.17, 0.15, 0.1 μM of reduced metabolite (As[III]) were recorded from 1 μM of As(V)/P containing cultures of Sargassum horneri, Sargassum patens, and Pyropia yezoensis, respectively. On the other hand, 0.024 and 0.28 μM of methylated metabolite (DMAA[V]) were detected under the same culture conditions from Sargassum horneri and Pyropia yezoensis, respectively. The results also indicated that P in medium inhibits the intracellular uptake of As(V) and subsequent extrusion of biotransformed metabolites into the medium. These findings can help to understand the metabolic diversity of macroalgae species on As biogeochemistry in the marine environment.

Arsenic speciation and biotransformation by the marine macroalga Undaria pinnatifida in seawater: A culture medium study

Freshwater and marine organisms are capable of metabolizing arsenic (As) efficiently and regulating the As biogeochemical cycles. In this study, Undaria pinnatifida was exposed to As(V) (0, 0.1, and 1 μM) and phosphate (P; 1 and 10 μM) in seawater under laboratory-controlled conditions for up to seven days to analyze As biotransformation. The growth rates and chlorophyll fluorescence of the alga were unaffected by As stress, and statistically insignificant differences were observed among the cultures (p > 0.05). As(V) was readily accumulated by this macroalga through phosphate transporters, transformed intracellularly, and excreted into the medium, depending on the As(V) to P molar ratios. The concentration of As(V) and biotransformed species As(III) and DMAA(V) varied significantly in the algal cultures on the basis of the exposure period (p < 0.05). The concentration of As(III) was initially higher but decreased with the incubation period, whereas the concentration of DMAA(V) increased gradually. At the end of the incubation, 0.04 and 0.32 μM DMAA(V) were recorded in the media containing 0.1 and 1 μM As(V) with a constant 1.0 μM P, respectively. The results also indicated that the cellular uptake of As(V) and subsequent release of DMAA(V) were inhibited by P in the medium. The biotransformation was consistent with the As(V) detoxification mechanism based on reduction and methylation, which was enhanced by the lower As(V) to P molar ratios. These findings can be helpful in understanding the contribution of macroalgae to As biogeochemistry in marine environments and the potential risks of As dietary intake.

The gut microbiome is required for full protection against acute arsenic toxicity in mouse models

Arsenic poisons an estimated 200 million people worldwide through contaminated food and drinking water. Confusingly, the gut microbiome has been suggested to both mitigate and exacerbate arsenic toxicity. Here, we show that the microbiome protects mice from arsenic-induced mortality. Both antibiotic-treated and germ-free mice excrete less arsenic in stool and accumulate more arsenic in organs compared to control mice. Mice lacking the primary arsenic detoxification enzyme (As3mt) are hypersensitive to arsenic after antibiotic treatment or when derived germ-free, compared to wild-type and/or conventional counterparts. Human microbiome (stool) transplants protect germ-free As3mt-KO mice from arsenic-induced mortality, but protection depends on microbiome stability and the presence of specific bacteria, including Faecalibacterium. Our results demonstrate that both a functional As3mt and specific microbiome members are required for protection against acute arsenic toxicity in mouse models. We anticipate that the gut microbiome will become an important explanatory factor of disease (arsenicosis) penetrance in humans, and a novel target for prevention and treatment strategies.

It is unclear whether the gut microbiome can mitigate or exacerbate arsenic toxicity. Here, Coryell et al. show that the human gut microbiome protects mice from arsenic-induced mortality, with protection levels correlating with the relative abundance of the human commensal Faecalibacterium.

Titanium dioxide nanoparticles enhance inorganic arsenic bioavailability and methylation in two freshwater algae species

The effect of titanium dioxide nanoparticles (nano-TiO₂) on the bioaccumulation and biotransformation of arsenic (As) remains largely unknown. In this study, we exposed two freshwater algae (Microcystis aeruginosa and Scenedesmus obliquus) to inorganic As (arsenite and arsenate) with the aim of increasing our understanding on As bioaccumulation and methylation in the presence of nano-TiO₂. Direct evidence from transmission electron microscope (TEM) images show that nano-TiO₂ (anatase) entered exposed algae. Thus, nano-TiO₂ as carriers boosted As accumulation and methylation in these two algae species, which varied between inorganic As speciation and algae species. Specifically, nano-TiO₂ could markedly enhance arsenate (As(V)) accumulation in M. aeruginosa and arsenite (As(III)) accumulation in S. obliquus. Similarly, we found evidence of higher As methylation activity in the M. aeruginosa of As(III) 2 mg L^-1 nano-TiO₂ treatment. Although this was also true for the S. obliquus (As(V)) treatment, this species exhibited higher As methylation compared to M. aeruginosa, being more sensitive to As associated with nano-TiO₂ compared to M. aeruginosa. Due to changes in pH levels inside these exposed algae, As dissociation from nano-TiO₂ inside algal cells enhanced As methylation. Accordingly, the potential influence of nanoparticles on the bioaccumulation and biotransformation of their co-contaminants deserves more attention.

Phosphate starvation response controls genes required to synthesize the phosphate analog arsenate

Environmental arsenic poisoning affects roughly 200 million people worldwide. The toxicity and mobility of arsenic in the environment is significantly influenced by microbial redox reactions, with arsenite (As^III ) being more toxic than arsenate (As^V ). Microbial oxidation of As^III to As^V is known to be regulated by the AioXSR signal transduction system and viewed to function for detoxification or energy generation. Here, we show that As^III oxidation is ultimately regulated by the phosphate starvation response (PSR), requiring the sensor kinase PhoR for expression of the As^III oxidase structural genes aioBA. The PhoRB and AioSR signal transduction systems are capable of transphosphorylation cross-talk, closely integrating As^III oxidation with the PSR. Further, under PSR conditions, As^V significantly extends bacterial growth and accumulates in the lipid fraction to the apparent exclusion of phosphorus. This could spare phosphorus for nucleic acid synthesis or triphosphate metabolism wherein unstable arsenic esters are not tolerated, thereby enhancing cell survival potential. We conclude that As^III oxidation is logically part of the bacterial PSR, enabling the synthesis of the phosphate analog As^V to replace phosphorus in specific biomolecules or to synthesize other molecules capable of a similar function, although not for total replacement of cellular phosphate.

Arsenate biotransformation by Microcystis aeruginosa under different nitrogen and phosphorus levels

The arsenate (As(V)) biotransformation by Microcystis aeruginosa in a medium with different concentrations of nitrogen (N) and phosphorus (P) has been studied under laboratory conditions. When 15μg/L As(V) was added, N and P in the medium showed effective regulation on arsenic (As) metabolism in M. aeruginosa, resulting in significant differences in the algal growth among different N and P treatments. Under 0.2mg/L P treatment, increases in N concentration (4-20mg/L) significantly stimulated the cell growth and therefore indirectly enhanced the production of dimethylarsinic acid (DMA), the main As metabolite, accounting for 71%-79% of the total As in the medium. Meanwhile, 10-20mg/L N treatments accelerated the ability of As metabolization by M. aeruginosa, leading to higher contents of DMA per cell. However, As(V) uptake by M. aeruginosa was significantly impeded by 0.5-1.0mg/L P treatment, resulting in smaller rates of As transformation in M. aeruginosa as well as lower contents of As metabolites in the medium. Our data demonstrated that As(V) transformation by M. aeruginosa was significantly accelerated by increasing N levels, while it was inhibited by increasing P levels. Overall, both P and N play key roles in As(V) biotransformation processes.

Spatial and seasonal changes of arsenic species in Lake Taihu in relation to eutrophication

Spatial and seasonal variations of arsenic species in Lake Taihu (including Zhushan Bay, Meiliang Bay, Gonghu Bay, and Southern Taihu) were investigated. Relatively high levels of total arsenic (TAs) and arsenate (As(V)) were observed in hyper-eutrophic regions during summer and autumn, which is attributed to exogenous contamination and seasonal endogenous release from sediments. The distributions of TAs and As(V) were significantly affected by total phosphorus, iron, manganese, and dissolved organic carbon. Arsenite (As(III)) and methylarsenicals (the sum of monomethylarsenic acid (MMA(V)) and dimethylarsenic acid (DMA(V))), mainly from biotransformation of As(V), were affected by temperature-controlled microalgae activities and local water quality parameters, exhibiting significantly higher concentrations and proportions in hyper-eutrophic and middle eutrophic regions during summer compared to mesotrophic region. The eutrophic environment, which induces changes in the main water quality parameters such as phosphorus, chlorophyll-a, iron, manganese, and dissolved organic carbon, can favor the biogeochemical cycling of arsenic in the aquatic systems.

Anabaena sp. mediated bio-oxidation of arsenite to arsenate in synthetic arsenic (III) solution: Process optimization by response surface methodology

Blue green algae Anabaena sp. was cultivated in synthetic arsenite solution to investigate its bio-oxidation potential for arsenic species. Response surface methodology (RSM) was employed based on a 3-level full factorial design considering four factors, viz. initial arsenic (III) concentration, algal dose, temperature and time. Bio-oxidation (%) of arsenic (III) was considered as response for the design. The study revealed that about 100% conversion of As (III) to As (V) was obtained for initial As (III) concentration of 2.5-7.5 mg/L at 30 °C for 72 h of exposure using 3 g/L of algal dose signifying a unique bio-oxidation potential of Anabaena sp. The dissolved CO2 (DCO2) and oxygen (DO) concentration in solution was monitored during the process and based on the data, a probable mechanism was proposed wherein algal cell acts like a catalytic membrane surface and expedites the bio-oxidation process. Bioaccumulation of arsenic, as well as, surface adsorption on algal cell was found considerably low. Lipid content of algal biomass grown in arsenite solution was found slightly lower than that of algae grown in synthetic media. Toxicity effects on algal cells due to arsenic exposure were evaluated in terms of comet assay and chlorophyll a content which indicated DNA damage to some extent along with very little decrease in chlorophyll a content. In summary, the present study explored the potential application of Anabaena sp. as an ecofriendly and sustainable option for detoxification of arsenic contaminated natural water with value-added product generation.

Effect of Metals, Metalloids and Metallic Nanoparticles on Microalgae Growth and Industrial Product Biosynthesis: A Review

Microalgae are a source of numerous compounds that can be used in many branches of industry. Synthesis of such compounds in microalgal cells can be amplified under stress conditions. Exposure to various metals can be one of methods applied to induce cell stress and synthesis of target products in microalgae cultures. In this review, the potential of producing diverse biocompounds (pigments, lipids, exopolymers, peptides, phytohormones, arsenoorganics, nanoparticles) from microalgae cultures upon exposure to various metals, is evaluated. Additionally, different methods to alter microalgae response towards metals and metal stress are described. Finally, possibilities to sustain high growth rates and productivity of microalgal cultures in the presence of metals are discussed.