Long-term acclimation to cadmium exposure reveals extensive phenotypic plasticity in Chlamydomonas.

Increasing industrial and anthropogenic activities are producing and releasing more and more pollutants in the environment. Among them, toxic metals are one of the major threats for human health and natural ecosystems. Because photosynthetic organisms play a critical role in primary productivity and pollution management, investigating their response to metal toxicity is of major interest. Here, the green microalga Chlamydomonas (Chlamydomonas reinhardtii) was subjected to short (3 d) or chronic (6 months) exposure to 50 µM cadmium (Cd), and the recovery from chronic exposure was also examined. An extensive phenotypic characterization and transcriptomic analysis showed that the impact of Cd on biomass production of short-term (ST) exposed cells was almost entirely abolished by long-term (LT) acclimation. The underlying mechanisms were initiated at ST and further amplified after LT exposure resulting in a reversible equilibrium allowing biomass production similar to control condition. This included modification of cell wall-related gene expression and biofilm-like structure formation, dynamics of metal ion uptake and homeostasis, photosynthesis efficiency recovery and Cd acclimation through metal homeostasis adjustment. The contribution of the identified coordination of phosphorus and iron homeostasis (partly) mediated by the main phosphorus homeostasis regulator, Phosphate Starvation Response 1, and a basic Helix-Loop-Helix transcription factor (Cre05.g241636) was further investigated. The study reveals the highly dynamic physiological plasticity enabling algal cell growth in an extreme environment.

Electrospinning of Electroconductive Water-Resistant Nanofibers of PEDOT-PSS, Cellulose Nanofibrils and PEO: Fabrication, Characterization, and Cytocompatibility.

Electrically conductive composite nanofibers were fabricated using poly(3,4-ethylenedioxythiophene) doped with poly(styrenesulfonate) (PEDOT-PSS) and cellulose nanofibrils (CNFs) via the electrospinning technique. Poly(ethylene oxide) (PEO) was used to assist the electrospinning process, and poly(ethylene glycol) diglycidyl ether was used to induce chemical cross-linking, enabling stability of the formed fibrous mats in water. The experimental parameters regarding the electrospinning polymer dispersion and electrospinning process were carefully studied to achieve a reproducible method to obtain bead-free nanofibrous mats with high stability after water contact, with an electrical conductivity of 13 ± 5 S m-1, thus making them suitable for bioelectrochemical applications. The morphology of the electrospun nanofibers was characterized by scanning electron microscopy, and the C/S ratio was determined with energy dispersive X-ray analysis. Cyclic voltammetric studies showed that the PEDOT-PSS/CNF/PEO composite fibers exhibited high electroactivity and high stability in water for at least two months. By infrared spectroscopy, the slightly modified fiber morphology after water contact was demonstrated to be due to dissolution of some part of the PEO in the fiber structure. The biocompatibility of the PEDOT-PSS/CNF/PEO composite fibers when used as an electroconductive substrate to immobilize microalgae and cyanobacteria in a photosynthetic bioelectrochemical cell was also demonstrated.

Determination of hazardous concentrations of 2,4-dinitrophenol in freshwater ecosystems based on species sensitivity distributions.

2,4-dinitrophenol (2,4-DNP) is a phenolic compound used as a wood preservative or pesticide. The chemical is hazardous to freshwater organisms. Although 2,4-DNP poses ecological risks, only a few of its aquatic environmental risks have been investigated and very limited guidelines for freshwater aquatic ecosystems have been established by governments. This study addresses the paucity of 2,4-DNP toxicity data for freshwater ecosystems and the current lack of highly reliable trigger values for this highly toxic compound. We conducted acute bioassays using 12 species from nine taxonomic groups and chronic assays using five species from four taxonomic groups to improve the quality of the dataset and enable the estimation of protective concentrations based on species sensitivity distributions. The acute and hazardous concentrations of 2,4-DNP in 5% of freshwater aquatic species (HC5) were determined to be 0.91 (0.32-2.65) mg/L and 0.22 (0.11-0.42) mg/L, respectively. To the best of our knowledge, this is the first report of a suggested chronic HC5 for 2,4-DNP and it provides the much-needed fundamental data for the risk assessment and management of freshwater ecosystems.

Toxicity, Physiological, and Ultrastructural Effects of Arsenic and Cadmium on the Extremophilic Microalga Chlamydomonas acidophila.

The cytotoxicity of cadmium (Cd), arsenate (As(V)), and arsenite (As(III)) on a strain of Chlamydomonas acidophila, isolated from the Rio Tinto, an acidic environment containing high metal(l)oid concentrations, was analyzed. We used a broad array of methods to produce complementary information: cell viability and reactive oxygen species (ROS) generation measures, ultrastructural observations, transmission electron microscopy energy dispersive x-ray microanalysis (TEM-XEDS), and gene expression. This acidophilic microorganism was affected differently by the tested metal/metalloid: It showed high resistance to arsenic while Cd was the most toxic heavy metal, showing an LC50 = 1.94 µM. Arsenite was almost four-fold more toxic (LC50= 10.91 mM) than arsenate (LC50 = 41.63 mM). Assessment of ROS generation indicated that both arsenic oxidation states generate superoxide anions. Ultrastructural analysis of exposed cells revealed that stigma, chloroplast, nucleus, and mitochondria were the main toxicity targets. Intense vacuolization and accumulation of energy reserves (starch deposits and lipid droplets) were observed after treatments. Electron-dense intracellular nanoparticle-like formation appeared in two cellular locations: inside cytoplasmic vacuoles and entrapped into the capsule, around each cell. The chemical nature (Cd or As) of these intracellular deposits was confirmed by TEM-XEDS. Additionally, they also contained an unexpected high content in phosphorous, which might support an essential role of poly-phosphates in metal resistance.

Salicylic acid and aspirin stimulate growth of Chlamydomonas and inhibit lipoxygenase and chloroplast desaturase pathways.

Chemical stimulants, used to enhance biomass yield, are highly desirable for the commercialisation of algal products for a wide range of applications in the food, pharma and biofuels sectors. In the present study, phenolic compounds, varying in substituents and positional isomers on the arene ring have been evaluated to determine structure-activity relationship and growth. The phenols, catechol, 4-methylcatechol and 2, 4-dimethyl phenol were generally inhibitory to growth as were the compounds containing an aldehyde function. By contrast, the phenolic acids, salicylic acid, aspirin and 4-hydroxybenzoate markedly stimulated cell proliferation enhancing cell numbers by 20-45% at mid-log phase. The order of growth stimulation was ortho > para > meta with respect to the position of the OH group. Both SA and aspirin reduced 16:3 in chloroplast galactolipids. In addition, both compounds inhibited lipoxygenase activity and lowered the levels of lipid hydroperoxides and malondialdehydes in the cells. The present study has demonstrated the possibility of using SA or aspirin to promote algal growth through the manipulation of lipid metabolising enzymes.

Metabolic, Physiological, and Transcriptomics Analysis of Batch Cultures of the Green Microalga Chlamydomonas Grown on Different Acetate Concentrations.

Acetate can be efficiently metabolized by the green microalga Chlamydomonasreinhardtii. The regular concentration is 17 mM, although higher concentrations are reported to increase starch and fatty acid content. To understand the responses to higher acetate concentrations, Chlamydomonas cells were cultivated in batch mode in the light at 17, 31, 44, and 57 mM acetate. Metabolic analyses show that cells grown at 57 mM acetate possess increased contents of all components analyzed (starch, chlorophylls, fatty acids, and proteins), with a three-fold increased volumetric biomass yield compared to cells cultivated at 17 mM acetate at the entry of stationary phase. Physiological analyses highlight the importance of photosynthesis for the low-acetate and exponential-phase samples. The stationary phase is reached when acetate is depleted, except for the cells grown at 57 mM acetate, which still divide until ammonium exhaustion. Surprisal analysis of the transcriptomics data supports the biological significance of our experiments. This allows the establishment of a model for acetate assimilation, its transcriptional regulation and the identification of candidates for genetic engineering of this metabolic pathway. Altogether, our analyses suggest that growing at high-acetate concentrations could increase biomass productivities in low-light and CO2-limiting air-bubbled medium for biotechnology.

Manganese co-localizes with calcium and phosphorus in Chlamydomonas acidocalcisomes and is mobilized in manganese-deficient conditions.

Exposing cells to excess metal concentrations well beyond the cellular quota is a powerful tool for understanding the molecular mechanisms of metal homeostasis. Such improved understanding may enable bioengineering of organisms with improved nutrition and bioremediation capacity. We report here that Chlamydomonas reinhardtii can accumulate manganese (Mn) in proportion to extracellular supply, up to 30-fold greater than its typical quota and with remarkable tolerance. As visualized by X-ray fluorescence microscopy and nanoscale secondary ion MS (nanoSIMS), Mn largely co-localizes with phosphorus (P) and calcium (Ca), consistent with the Mn-accumulating site being an acidic vacuole, known as the acidocalcisome. Vacuolar Mn stores are accessible reserves that can be mobilized in Mn-deficient conditions to support algal growth. We noted that Mn accumulation depends on cellular polyphosphate (polyP) content, indicated by 1) a consistent failure of C. reinhardtii vtc1 mutant strains, which are deficient in polyphosphate synthesis, to accumulate Mn and 2) a drastic reduction of the Mn storage capacity in P-deficient cells. Rather surprisingly, X-ray absorption spectroscopy, EPR, and electron nuclear double resonance revealed that only little Mn2+ is stably complexed with polyP, indicating that polyP is not the final Mn ligand. We propose that polyPs are a critical component of Mn accumulation in Chlamydomonas by driving Mn relocation from the cytosol to acidocalcisomes. Within these structures, polyP may, in turn, escort vacuolar Mn to a number of storage ligands, including phosphate and phytate, and other, yet unidentified, compounds.

Remodeling of Chlamydomonas Metabolism Using Synthetic Inducers Results in Lipid Storage during Growth.

Microalgae accumulate lipids during stress such as that of nutrient deprivation, concomitant with cessation of growth and depletion of chloroplasts. By contrast, certain small chemical compounds selected by high-throughput screening in Chlamydomonas reinhardtii can induce lipid accumulation during growth, maintaining biomass. Comprehensive pathway analyses using proteomics, transcriptomics, and metabolomics data were acquired from Chlamydomonas cells grown in the presence of one of two structurally distinct lipid activators. WD10784 stimulates both starch and lipid accumulation, whereas WD30030-treated cells accumulate only lipids. The differences in starch accumulation are largely due to differential effects of the two compounds on substrate levels that feed into starch synthesis and on genes encoding starch metabolic enzymes. The compounds had differential effects on photosynthesis, respiration, and oxidative stress pathways. Cells treated with WD10784 showed slowed growth over time and reduced abundance of photosynthetic proteins, decreased respiration, and increased oxidative stress proteins, glutathione, and reactive oxygen species specific to this compound. Both compounds maintained central carbon and nitrogen metabolism, including the tricarboxylic acid cycle, glycolysis, respiration, and the Calvin-Benson-Bassham cycle. There were few changes in proteins and transcripts related to fatty acid biosynthesis, whereas proteins and transcripts for triglyceride production were elevated, suggesting that lipid synthesis is largely driven by substrate availability. This study reports that the compound WD30030 and, to a lesser extent WD10784, increases lipid and lipid droplet synthesis and storage without restricting growth or biomass accumulation by mechanisms that are substantially different from nutrient deprivation.

Monoalkyl Tin Nano-Cluster Films Reveal a Low Environmental Impact under Simulated Natural Conditions.

Recently, monoalkyl oxo-hydroxo tin clusters have emerged as a new class of metal-oxide resist to support the semiconductor industry's transition to extreme ultraviolet (EUV) lithography. Under EUV exposure, these tin-based clusters exhibit higher performance and wider process windows than conventional polymer materials. A promising new monoalkyl precursor, [(BuSn)12 O14 (OH)6 ][OH]2 (BuSn), is still in its infancy in terms of film formation. However, understanding potential environmental effects could significantly affect future development as a commercial product. We synthesized and explored the toxicity of nano-BuSn in the alga Chlamydomonas reinhardtii and the crustacean Daphnia magna at exposure concentrations ranging from 0 to 250 mg/L. Nano-BuSn had no effect on C. reinhardtii growth rate irrespective of concentration, whereas high nanoparticle concentrations (≥100 mg/L) increased D. magna immobilization and mortality significantly. To simulate an end-of-life disposal and leachate contamination, BuSn-coated film wafers were incubated in water at various pH values and temperatures for 14 and 90 d to investigate leaching rates and subsequent toxicity of the leachates. Although small quantities of tin (1.1-3.4% of deposited mass) leached from the wafers, it was insufficient to elicit a toxic response regardless of pH, incubation time, or temperature. The low toxicity of the tin-based thin films suggests that they can be an environmentally friendly addition to the material sets useful for semiconductor manufacturing. Environ Toxicol Chem 2019;38:2651-2658. © 2019 SETAC.

Evaluation of algal photosynthesis inhibition activity for dissolved organic matter with the consideration of inorganic and coloring constituents.

The effect of waterborne ingredient on ecosystem has been of great interest. In the present study, the evaluation method using algal photosynthesis inhibition assay with dual-channel pulse amplitude modulation (PAM) system was established for a series of water samples to elucidate the potential effect of the total body of organic compounds including natural organic matter (NOM) on aquatic ecosystems. The more sensitive and less time-consuming monitoring method compared with algal growth inhibition assay was suggested, especially considering inorganic and coloring constituents. Algal photosynthesis inhibition activity was detected with high sensitivity for photosystem II (PSII) inhibitors, whereas the IC10 of the other chemicals was over the environmental standard concentration for Chlamydomonas moewusii (Chlorophyceae) and Pheodactylum tricornutum (Diatomea). The photosynthesis inhibition activity of Lake Biwa dissolved organic matter (LBDOM) and fulvic acid (LBFA) was significantly detected at ≥10 times the concentration and >10 mgC L-1, respectively, whereas prominent activity was confirmed for Suwannee River NOM (SRNOM) on the river original concentration (>30 mgC L-1) for both algae. Significant inhibition activity was detected in both algae at least in twice-concentration for water samples from a wastewater treatment pilot plant. There was no great difference in the activity between sewage secondary effluent and its filtrate with ultrafiltration (UF), and physically washing water for the UF membrane.

A highly efficient sulfadiazine selection system for the generation of transgenic plants and algae.

The genetic transformation of plant cells is critically dependent on the availability of efficient selectable marker gene. Sulfonamides are herbicides that, by inhibiting the folic acid biosynthetic pathway, suppress the growth of untransformed cells. Sulfonamide resistance genes that were previously developed as selectable markers for plant transformation were based on the assumption that, in plants, the folic acid biosynthetic pathway resides in the chloroplast compartment. Consequently, the Sul resistance protein, a herbicide-insensitive dihydropteroate synthase, was targeted to the chloroplast. Although these vectors produce transgenic plants, the transformation efficiencies are low compared to other markers. Here, we show that this inefficiency is due to the erroneous assumption that the folic acid pathway is located in chloroplasts. When the RbcS transit peptide was replaced by a transit peptide for protein import into mitochondria, the compartment where folic acid biosynthesis takes place in yeast, much higher resistance to sulfonamide and much higher transformation efficiencies are obtained, suggesting that current sul vectors are likely to function due to low-level mistargeting of the resistance protein to mitochondria. We constructed a series of optimized transformation vectors and demonstrate that they produce transgenic events at very high frequency in both the seed plant tobacco and the green alga Chlamydomonas reinhardtii. Co-transformation experiments in tobacco revealed that sul is even superior to nptII, the currently most efficient selectable marker gene, and thus provides an attractive marker for the high-throughput genetic transformation of plants and algae.

Proteome evolution under non-substitutable resource limitation.

Resource limitation is a major driver of the ecological and evolutionary dynamics of organisms. Short-term responses to resource limitation include plastic changes in molecular phenotypes including protein expression. Yet little is known about the evolution of the molecular phenotype under longer-term resource limitation. Here, we combine experimental evolution of the green alga Chlamydomonas reinhardtii under multiple different non-substitutable resource limitation regimes with proteomic measurements to investigate evolutionary adaptation of the molecular phenotype. We demonstrate convergent proteomic evolution of core metabolic functions, including the Calvin-Benson cycle and gluconeogenesis, across different resource limitation environments. We do not observe proteomic changes consistent with optimized uptake of particular limiting resources. Instead, we report that adaptation proceeds in similar directions under different types of non-substitutable resource limitation. This largely convergent evolution of the expression of core metabolic proteins is associated with an improvement in the resource assimilation efficiency of nitrogen and phosphorus into biomass.

Interorganelle Communication: Peroxisomal MALATE DEHYDROGENASE2 Connects Lipid Catabolism to Photosynthesis through Redox Coupling in Chlamydomonas.

Plants and algae must tightly coordinate photosynthetic electron transport and metabolic activities given that they often face fluctuating light and nutrient conditions. The exchange of metabolites and signaling molecules between organelles is thought to be central to this regulation but evidence for this is still fragmentary. Here, we show that knocking out the peroxisome-located MALATE DEHYDROGENASE2 (MDH2) of Chlamydomonas reinhardtii results in dramatic alterations not only in peroxisomal fatty acid breakdown but also in chloroplast starch metabolism and photosynthesis. mdh2 mutants accumulated 50% more storage lipid and 2-fold more starch than the wild type during nitrogen deprivation. In parallel, mdh2 showed increased photosystem II yield and photosynthetic CO2 fixation. Metabolite analyses revealed a >60% reduction in malate, together with increased levels of NADPH and H2O2 in mdh2 Similar phenotypes were found upon high light exposure. Furthermore, based on the lack of starch accumulation in a knockout mutant of the H2O2-producing peroxisomal ACYL-COA OXIDASE2 and on the effects of H2O2 supplementation, we propose that peroxisome-derived H2O2 acts as a regulator of chloroplast metabolism. We conclude that peroxisomal MDH2 helps photoautotrophs cope with nitrogen scarcity and high light by transmitting the redox state of the peroxisome to the chloroplast by means of malate shuttle- and H2O2-based redox signaling.

Decreased phosphorus incorporation explains the negative effect of high iron concentrations in the green microalga Chlamydomonas acidophila.

The green microalga Chlamydomonas acidophila is an important primary producer in very acidic lakes (pH 2.0-3.5), characterized by high concentrations of ferric iron (up to 1 g total Fe L-1) and low rates of primary production. It was previously suggested that these high iron concentrations result in high iron accumulation and inhibit photosynthesis in C. acidophila. To test this, the alga was grown in sterilized lake water and in medium with varying total iron concentrations under limiting and sufficient inorganic phosphorus (Pi) supply, because Pi is an important growth limiting nutrient in acidic waters. Photosynthesis and growth of C. acidophila as measured over 5 days were largely unaffected by high total iron concentrations and only decreased if free ionic Fe3+ concentrations exceeded 100 mg Fe3+ L-1. Although C. acidophila was relatively rich in iron (up to 5 mmol Fe: mol C), we found no evidence of iron toxicity. In contrast, a concentration of 260 mg total Fe L-1 (i.e. 15 mg free ionic Fe3+ L-1), which is common in many acidic lakes, reduced Pi-incorporation by 50% and will result in Pi-limited photosynthesis. The resulting Pi-limitation present at high iron and Pi concentrations was illustrated by elevated maximum Pi-uptake rates. No direct toxic effects of high iron were found, but unfavourable chemical Pi-speciation reduced growth of the acidophile alga.

Basis of genetic adaptation to heavy metal stress in the acidophilic green alga Chlamydomonas acidophila.

To better understand heavy metal tolerance in Chlamydomonas acidophila, an extremophilic green alga, we assembled its transcriptome and measured transcriptomic expression before and after Cd exposure in this and the neutrophilic model microalga Chlamydomonas reinhardtii. Genes possibly related to heavy metal tolerance and detoxification were identified and analyzed as potential key innovations that enable this species to live in an extremely acid habitat with high levels of heavy metals. In addition we provide a data set of single orthologous genes from eight green algal species as a valuable resource for comparative studies including eukaryotic extremophiles. Our results based on differential gene expression, detection of unique genes and analyses of codon usage all indicate that there are important genetic differences in C. acidophila compared to C. reinhardtii. Several efflux family proteins were identified as candidate key genes for adaptation to acid environments. This study suggests for the first time that exposure to cadmium strongly increases transposon expression in green algae, and that oil biosynthesis genes are induced in Chlamydomonas under heavy metal stress. Finally, the comparison of the transcriptomes of several acidophilic and non-acidophilic algae showed that the Chlamydomonas genus is polyphyletic and that acidophilic algae have distinctive aminoacid usage patterns.

PtDRG1, a Desiccation Response Gene from Pyropia tenera (Rhodophyta), Exhibits Chaperone Function and Enhances Abiotic Stress Tolerance.

Pyropia are commercially valuable marine red algae that grow in the intertidal zone. They are extremely tolerant to desiccation stress. We have previously identified and reported desiccation response genes (DRGs) based on transcriptome analysis of P. tenera. Among them, PtDRG1 encodes a polypeptide of 22.6 kDa that is located in the chloroplast. PtDRG1 does not share sequence homology with any known gene deposited in public database. Transcription of PtDRG1 gene was upregulated by osmotic stress induced by mannitol or H2O2 as well as desiccation stress, but not by heat. When PtDRG1 was overexpressed in Escherichia coli or Chlamydomonas, transformed cells grew much better than control cells under high temperature as well as osmotic stress induced by mannitol and NaCl. In addition, PtDRG1 significantly reduced thermal aggregation of substrate protein under heat stress condition. These results demonstrate that PtDRG1 has a chaperone function and plays a role in tolerance mechanism for abiotic stress. This study shows that red algae have unknown stress proteins such as PtDRG1 that contributes to stress tolerance.

Biological effects of four iron-containing nanoremediation materials on the green alga Chlamydomonas sp.

As nanoremediation strategies for in-situ groundwater treatment extend beyond nanoiron-based applications to adsorption and oxidation, ecotoxicological evaluations of newly developed materials are required. The biological effects of four new materials with different iron (Fe) speciations ([i] FerMEG12 - pristine flake-like milled Fe(0) nanoparticles (nZVI), [ii] Carbo-Iron® - Fe(0)-nanoclusters containing activated carbon (AC) composite, [iii] Trap-Ox® Fe-BEA35 (Fe-zeolite) - Fe-doped zeolite, and [iv] Nano-Goethite - 'pure' FeOOH) were studied using the unicellular green alga Chlamydomonas sp. as a model test system. Algal growth rate, chlorophyll fluorescence, efficiency of photosystem II, membrane integrity and reactive oxygen species (ROS) generation were assessed following exposure to 10, 50 and 500 mg L-1 of the particles for 2 h and 24 h. The particles had a concentration-, material- and time-dependent effect on Chlamydomonas sp., with increased algal growth rate after 24 h. Conversely, significant intracellular ROS levels were detected after 2 h, with much lower levels after 24 h. All Fe-nanomaterials displayed similar Z-average sizes and zeta-potentials at 2 h and 24 h. Effects on Chlamydomonas sp. decreased in the order FerMEG12 > Carbo-Iron® > Fe-zeolite > Nano-Goethite. Ecotoxicological studies were challenged due to some particle properties, i.e. dark colour, effect of constituents and a tendency to agglomerate, especially at high concentrations. All particles exhibited potential to induce significant toxicity at high concentrations (500 mg L-1), though such concentrations would rapidly decrease to mg or µg L-1 in aquatic environments, levels harmless to Chlamydomonas sp. The presented findings contribute to the practical usage of particle-based nanoremediation in environmental restoration.

H+- and Na+- elicited rapid changes of the microtubule cytoskeleton in the biflagellated green alga Chlamydomonas.

Although microtubules are known for dynamic instability, the dynamicity is considered to be tightly controlled to support a variety of cellular processes. Yet diverse evidence suggests that this is not applicable to Chlamydomonas, a biflagellate fresh water green alga, but intense autofluorescence from photosynthesis pigments has hindered the investigation. By expressing a bright fluorescent reporter protein at the endogenous level, we demonstrate in real time discreet sweeping changes in algal microtubules elicited by rises of intracellular H+ and Na+. These results from this model organism with characteristics of animal and plant cells provide novel explanations regarding how pH may drive cellular processes; how plants may respond to, and perhaps sense stresses; and how organisms with a similar sensitive cytoskeleton may be susceptible to environmental changes.

Cloning and Stress-Induced Expression Analysis of Calmodulin in the Antarctic Alga Chlamydomonas sp. ICE-L.

Calmodulin (CaM) is a Ca2+-binding protein that plays a role in several Ca2+ signaling pathways, which dynamically regulates the activities of hundreds of proteins. The ice alga Chlamydomonas sp. ICE-L, which has the ability to adapt to extreme polar conditions, is a crucial primary producer in Antarctic ecosystem. This study hypothesized that Cam helps the ICE-L to adapt to the fluctuating conditions in the polar environment. It first verified the overall length of Cam, through RT-PCR and RACE-PCR, based on partial Cam transcriptome library of ICE-L. Then, the nucleotide and predicted amino acid sequences were, respectively, analyzed by various bioinformatics approaches to gain more insights into the computed physicochemical properties of the CaM. Potential involvements of Cam in responding to certain stimuli (i.e., UVB radiation, high salinity, and temperature) were investigated by differential expression, measuring its transcription levels by means of quantitative RT-PCR. Results showed that CaM was indeed inducible and regulated by high UVB radiation, high salinity, and nonoptimal temperature conditions. Different conditions had different expression tendencies, which provided an important basis for investigating the adaptation mechanism of Cam in ICE-L.

Ciprofloxacin toxicity and its co-metabolic removal by a freshwater microalga Chlamydomonas mexicana.

This study evaluated the toxicity and cellular stresses of ciprofloxacin (CIP) and its co-metabolic removal in a freshwater microalga Chlamydomonas mexicana. The toxicological effects of CIP on C. mexicana were assessed by studying the growth and biochemical characteristics of the microalga including total chlorophyll, carotenoid content, malondialdehyde (MDA) and superoxide dismutase (SOD) activity. The calculated effective concentration (EC50) of CIP on C. mexicana was 65±4mgL-1 at 96h. The growth of C. mexicana was significantly inhibited at increased concentrations of CIP, showing 36±1, 75±3. and 88±3% inhibition at 40, 60 and 100mgL-1 CIP, respectively, compared to the control after 11days of cultivation. The total chlorophyll, carotenoid, MDA and SOD activity were significantly increased as a result of relatively high concentrations of CIP stress. C. mexicana showed 13±1% removal of CIP (2mgL-1) after 11days of cultivation; however, the addition of an electron donor (sodium acetate, 4gL-1) highly enhanced the removal of CIP (2mgL-1) by>3-fold after 11days. Kinetic studies showed that removal of CIP followed a first-order model (R2 0.94-0.97) with the apparent rate constants (k) ranging from 0.0121 to 0.079 d-1.