Coccomyxa Subellipsoidea Research Articles

Vanillin production by Corynebacterium glutamicum using heterologous aromatic carboxylic acid reductases.

Vanillin is a flavoring substance derived from vanilla. We are currently developing a biotransformation method for vanillin production using glucose. This report describes the last step in vanillin production: the conversion of vanillic acid to vanillin. First, we selected Corynebacterium glutamicum as the host owing to its high vanillin resistance. The aromatic aldehyde reductase gene (NCgl0324) and vanillic acid demethylase protein subunits A and B gene (vanAB, NCgl2300-NCgl2301) were deleted in C. glutamicum genome to avoid vanillin degradation. Next, we searched for an aromatic carboxylic acid reductase (ACAR), which converts vanillic acid to vanillin. Seventeen ACAR homologs from various organisms were introduced into C. glutamicum. In vivo conversion experiments showed that eight ACARs were successfully expressed and produced vanillin. In terms of conversion activity and substrate specificity, the ACARs from Gordonia effusa, Coccomyxa subellipsoidea, and Novosphingobium malaysiense are promising candidates for commercial production. Corynebacterium glutamicum harboring Gordonia effusa ACAR produced 22g/L vanillin, which is, to the best of our knowledge, the highest accumulation reported in the literature. At the same time, we discovered ACAR from Novosphingobium malaysiense and Coccomyxa subellipsoidea C-169 with high substrate specificity. These findings are useful for reducing the byproducts.

Near telomere-to-telomere genome assemblies of two Chlorella species unveil the composition and evolution of centromeres in green algae

BackgroundCentromeres play a crucial and conserved role in cell division, although their composition and evolutionary history in green algae, the evolutionary ancestors of land plants, remains largely unknown.ResultsWe constructed near telomere-to-telomere (T2T) assemblies for two Trebouxiophyceae species, Chlorella sorokiniana NS4-2 and Chlorella pyrenoidosa DBH, with chromosome numbers of 12 and 13, and genome sizes of 58.11 Mb and 53.41 Mb, respectively. We identified and validated their centromere sequences using CENH3 ChIP-seq and found that, similar to humans and higher plants, the centromeric CENH3 signals of green algae display a pattern of hypomethylation. Interestingly, the centromeres of both species largely comprised transposable elements, although they differed significantly in their composition. Species within the Chlorella genus display a more diverse centromere composition, with major constituents including members of the LTR/Copia, LINE/L1, and LINE/RTEX families. This is in contrast to green algae including Chlamydomonas reinhardtii, Coccomyxa subellipsoidea, and Chromochloris zofingiensis, in which centromere composition instead has a pronounced single-element composition. Moreover, we observed significant differences in the composition and structure of centromeres among chromosomes with strong collinearity within the Chlorella genus, suggesting that centromeric sequence evolves more rapidly than sequence in non-centromeric regions.ConclusionsThis study not only provides high-quality genome data for comparative genomics of green algae but gives insight into the composition and evolutionary history of centromeres in early plants, laying an important foundation for further research on their evolution.

Coccomyxa subellipsoidea KJ Components Enhance the Expression of Metallothioneins and Th17 Cytokines during Human T Cell Activation.

Coccomyxa subellipsoidea KJ (C-KJ) is a green alga with unique immunoregulatory characteristics. Here, we investigated the mechanism underlying the modification of T cell function by C-KJ components. The water-soluble extract of C-KJ was fractionated into protein (P) and sugar (S) fractions acidic (AS), basic (BS), and neutral (NS). These fractions were used for the treatment of peripheral blood mononuclear cells stimulated with toxic shock syndrome toxin-1. Transcriptome analysis revealed that both P and AS enhanced the expression of the genes encoding metallothionein (MT) family proteins, inflammatory factors, and T helper (Th) 17 cytokine and suppressed that of those encoding Th2 cytokines in stimulated T cells. The kinetics of MT1 and MT2A gene expression showed a transient increase in MT1 and maintenance of MT2A mRNA after T cell stimulation in the presence of AS. The kinetics of Th17-related cytokine secretion in the early period were comparable to those of MT2A mRNA. Furthermore, our findings revealed that static, a STAT-3 inhibitor, significantly suppressed MT2A gene expression. These findings suggest that the expression of MTs is involved in the immune regulatory function of C-KJ components, which is partially regulated by Th17 responses, and may help develop innovative immunoregulatory drugs or functional foods.

Coculture of Chlorella protothecoides and Coccomyxa subellipsoidea enhances cell growth and lipid accumulation: An effective strategy for biodiesel production

Microalgae coculture could resist impurities contamination and fulfill many special biosynthetic processes than microalga monoculture, which might be one of the potential strategies in boosting lipid productivity for biodiesel industrialization. This study explored the possibilities of coculturing of Chlorella protothecoides (CP) and Coccomyxa subellipsoidea (CS) in terms of enhanced cell growth and lipid accumulation. Dual-species coculture with a CP:CS inoculation ratio of 3:7 and a carbon/nitrogen (C/N) ratio of 32 achieved a biomass yield of 6.91 g/L and lipid productivity of 1.07 g/L/d, respectively, representing 1.41- to 1.70- and 3.05- to 3.10-fold increases over the values from dual species monoculture. This dual-species consortium also had increased proportions of C16–C18 (>96 %) and C18:1 fatty acid (50.27 %), providing excellent feedstock for biodiesel production. Furthermore, the CP and CS coculture had a shorter 4-day logarithmic growth cycle than either the CP (5-day) or CS (6-day) monoculture alone. Transcriptomic and metabolomic data indicated that CP and CS in dual-species consortium each performed specific tasks: CP increased the carbon sink and decreased lipid β-oxidation, while CS secreted beneficial factors to the extracellular environment to resist contamination with pathogens and stabilize pH fluctuations, thus supporting lipid accumulation. Exogenous metabolite melatonin (50 μM) supplementation further promoted the biomass and lipid content of coculture CP and CS to reach 9.27 g/L and 69.86 %. This mutualistic interaction strategy involving the use of CP and CS to boost lipid productivity could promote development in the industrial field of biodiesel production.

Paracetamol biodegradation coupling lipid biosynthesis in acclimated microalgae Coccomyxa subellipsoidea

Paracetamol (PAR) has received increasing concern due to its large usage, ubiquitous detection in environment and high ecotoxicology risk. This study investigated the effect of PAR on the growth and lipid production of Coccomyxa subellipsoidea, removal of PAR by C. subellipsoidea, and the metabolic difference in C. subellipsoidea after exposure to PAR. The PAR promoted C. subellipsoidea growth but the biomass increment reduced with PAR concentration increasing. Acclimation evolution could enhance removal capacity of C. subellipsoidea to PAR. Compared to wild C. subellipsoidea, the removal percentage of PAR by acclimated C. subellipsoidea increased 2.71-fold, the content and yield of lipid as well as the content of unsaturated fatty acid in acclimated C. subellipsoidea significantly increased by 1.06-, 1.13- and 1.12-fold, respectively. The metabolism fate of PAR analysis revealed that p-aminophenol was the first step degradadation product, and the molecular docking simulating suggested p-aminophenol was the most prone to undergo metabolism. Differential metabolites analysis showed that the up-regulating glutathione with 2.20-fold in C. subellipsoidea withstanded oxidative stress from PAR and actuated the PAR degradation, the up-regulating citric acid and fumarate as well as malate used as precursor of lipid biosynthesis actuated lipid accumulation. This work provides new insights for using microalgae for efficient treatment of wastewater containing pharmaceuticals contaminants (PCs) coupling high value-added products production.

High-efficient CO2-to-protein bioconversion by oleaginous Coccomyxa subellipsoidea using light quality shift and nitrogen supplementation strategy

Oleaginous microalgae are usually used in CO2-to-lipid bioprocess for biofuels production but still faced the low productivity of biomass and lipid with uncompetitive cost. A novel CO2-to-protein bioconversion pattern by oleaginous Coccomyxa subellipsoidea was implemented in the present work as high-value application of CO2. Results demonstrated that the highest CO2 fixation rate (RCO2, 0.74 g/L/d) and protein productivity (178 mg/L/d) with lower protein content (42.33% DW) were achieved under red light; but under blue light, the highest protein content (52.07% DW) were reached with lower productivity (156.94 mg/L/d) and RCO2 (0.52 g/L/d). The analysis of key genes transcription and enzymes activity revealed that red light boosted the photosynthetic activity and photoprotection contributing to the high-efficient CO2 fixation. Based on this, a tailored light quality shift and nitrogen supplementation in a two-phase culture (red light in phase 1; red: blue-1:1 with nitrate addition in phase 2) was developed, reaching the maximal biomass yield (6.12 g/L), RCO2 (0.90 g/L/d), protein content (52.00% DW) with protein productivity (265.83 mg/L/d) simultaneously, 2.0-fold, 1.2-fold, 2.9-fold and 2.3-fold higher than that under white light as the control. The highest contents of AAs (47.12% DW) and EAAs (18.67% DW) with essential amino acid index (1.3) were achieved, superior to FAO/WHO reference. Time-dependent gene transcription analysis revealed the up-regulated photosynthesis and nitrogen assimilation in the two-phase culture. This work demonstrated that the oleaginous C. subellipsoidea could be well used for protein production and CO2 fixation, providing a promising application approach in carbon neutrality and high-yield protein production.

Mechanisms of temperature acclimatisation in the psychrotolerant green alga Coccomyxa subellipsoidea C-169 (Trebouxiophyceae).

Despite the interest in different temperature acclimatisations of higher plants, few studies have considered the mechanisms that allow psychrotolerant microalgae to live in a cold environment. Although the analysis of the genomes of some algae revealed the presence of specific genes that encode enzymes that can be involved in the response to stress, this area has not been explored deeply. This work aims to clarify the acclimatisation mechanisms that enable the psychrotolerant green alga Coccomyxa subellipsoidea C-169 to grow in a broad temperature spectrum. The contents of various biochemical compounds in cells, the lipid composition of the biological membranes of entire cells, and the thylakoid fraction as well as the electron transport rate and PSII efficiency were investigated. The results demonstrate an acclimatisation mechanism that is specific for C. subellipsoidea and that allows the maintenance of appropriate membrane fluidity, for example, in thylakoid membranes. It is achieved almost exclusively by changes within the unsaturated fatty acid pool, like changes from C18:2 into C18:3 and C16:2 into C16:3 or vice versa. This ensures, for example, an effective transport rate through PSII and in consequence a maximum quantum yield of it in cells growing at different temperatures. Furthermore, reactions characteristic for both psychrotolerant and mesophilic microalgae, involving the accumulation of lipids and soluble sugars in cells at temperatures other than optimal, were observed. These findings add substantially to our understanding of the acclimatisation of psychrotolerant organisms to a wide range of temperatures and prove that this process could be accomplished in a species-specific manner.

Enhancement of carbon bio-fixation and lipid accumulation in Coccomyxa subellipsoidea with triethanolamine CO2 absorbent manipulation

The scenario probed carbon bio-fixation and lipid accumulation in Coccomyxa subellipsoidea with triethanolamine (TEA) CO2 absorbent manipulation. The results stated that CO2 bio-fixation (691.9 mg/L/d), CO2 utilization efficiency (57.84%), CO2 bio-fixation amount (3.86 g), biomass (2.58 g/L), and lipid accumulation (232.30 mg/L/d) in C. subellipsoidea with 100 mg/L TEA batch manipulation were separately 1.28-, 1.28-, 1.26-, 1.26-, and 1.72-fold more than that without TEA management. TEA fed-batch manipulation further augmented carbon fixation and the fixed carbon conversion into lipid with the maximum instantaneous CO2 fixation rate (1065.9 mg/L/d) and lipid productivity (538.7 mg/L/d) that were 1.97- and 3.98-fold more than that without TEA manipulation case. TEA manipulation also heightened the proportions of C16-C18 fatty acids (over 89%) and mono-unsaturated C18:1 (approximate 40.85%) which were commendable for high-quality biofuels-making. Such virtues were attributed to that TEA balanced pH fluctuation, converted CO2 into purposive HCO3- species, modulated glycolysis and TCA cycle to discharge appreciable energy, alleviated oxidative stress to block oxidative attack on lipids, and functioned as precursors to collectively boost CO2 sequestration and lipid accumulation in C. subellipsoidea. The outcomes were expected to provide exemplifications in developing win-win strategy for CO2 sequestration and lipid production by microalgae.

Enhancing carbon dioxide fixation and co-production of protein and lutein in oleaginous Coccomyxa subellipsoidea by a stepwise light intensity and nutrients feeding strategy

To achieve high-efficient CO2 fixation and co-production of protein and lutein, a stepwise light intensity and nutrients feeding strategy in two-phase cultivation was developed after optimization in one-phase culture of oleaginous C. subellipsoidea in this work. Results showed the incremental light intensity and CO2 feeding boosted biomass production in phase 1, then a decreased light intensity and CO2 feeding with nitrate addition enhanced protein and lutein synthesis in phase2. The highest biomass (9.40 g/L) and average CO2 fixation rate (1.4 g/L/d) were achieved with excellent content and productivity of protein (52.36% DW, 435.72 mg/L/d) and lutein (1.65 mg/g, 1.37 mg/L/d) with 40.27% of light-energy saved. While the highest contents of total amino acids (42.38% DW) and essential amino acids (17.65% DW) were obtained with an essential amino acid index (1.2) compared with FAO/WHO reference. This study provided a promising application scenario of oleaginous microalgae for carbon neutrality and multiple high-value compounds co-production.

Biomass and Lipid Production in the Aerial Microalga Coccomyxa subellipsoidea KGU-D001 in the Liquid and Aerial Phases

Biomass and Lipid Production in the Aerial Microalga Coccomyxa subellipsoidea KGU-D001 in the Liquid and Aerial Phases

Nitrogen-assisted lipid production by biofilms of aerial microalga Coccomyxa subellipsoidea KGU-D001 in the aerial phase.

The aerial microalga (Coccomyxa subellipsoidea KGU-D001) was photoautotrophically cultured under aerial phase conditions, and the influence of the nitrogen source on lipid production was investigated. Coccomyxa biofilms were introduced onto cotton wool using pure water (i.e., nutrient depletion) or a nitrogen-containing solution in a Petri dish, and they were cultured for 14days under aerial phase conditions. The biomass in the biofilm increased by more than 150% in 14days under nutrient depleted conditions and then increased further by approximately 30% following the addition of a nitrogen source. The lipid content rose under both nutrient depletion and nitrogen-added conditions, increasing by 170 and 150% in 14days, respectively. The protein and sugar contents were also monitored and analyzed. In the presence of a nitrogen source, C. subellipsoidea undergo cell division in a relatively short time span, and biomass and lipids can be synthesized under both nutrient depleted and nitrogen-added conditions.

Boosting concurrent lipid accumulation and secretion by Coccomyxa subellipsoidea with glucose coupling glycerol as accelerator

The scenario of this work was to boost concurrent lipid accumulation and secretion by Coccomyxa subellipsoidea with glucose coupling glycerol as accelerator. Results stated that glucose coupling glycerol (carbon content ratio 5:5) with batch-feeding achieved total lipid accumulation and lipids-secreted by 4.79 g/L and 2.4 g/L, representing 1.61- to −4.16 and 3.69- to 17.1-fold more than sole glucose and sole glycerol manipulation. When response to fed-batch fermentation with glucose coupling glycerol supplementation, lipid accumulation and lipids-secreted peaked 20.4 g/L and 9.11 g/L which performed 4.26- and 3.8-fold increments than batch-feeding manipulation. Whether intracellular lipidic or extracellular lipidic fatty acid profiles (mainly C16-C18) were commendable for high-quality biodiesel-making. Glucose coupling glycerol mobilized multiple channels including up-regulating PPP and glycolysis, weakening TCA cycle, and dampening MVA biosynthesis to flock acetyl-CoA into lipid accumulation. Such glucose coupling glycerol manipulation concurrently lowered PC/PE ratio to intensify cytomembrane fluidity and permeability consequently compelled lipid secretion. Findings provided exemplifications in facilitating concurrent lipid accumulation and secretion for economical-feasible alga-based biodiesel.

Co-cultures of Coccomyxa subellipsoidea and Psuedomonas denitrificans increases lipid accumulation independent of nutrient conditions

Coccomyxa subellipsoidea, a single-cell, eukaryotic green algae thriving in temperate climates, is capable of lipid accumulation in excess of 25 % (dry weight). At the front of agroeconomic challenges facing algae for the production of lipids in bioproduct development is how to effectively initiate lipid accumulation and harvesting with economically viable production costs. Co-culturing of the denitrifying bacteria Pseudomonas denitrificans with C. subellipsoidea increased total algal lipids levels, particularly neutral lipids when compared to C. subellipsoidea grown alone in BBM. Total lipid increased nearly two-fold to 16 % (dry weight); triacylglycerol (TAG) increased to 12.5 %. These findings suggest bacterial signaling induced lipid accumulation under nutrient rich condition coincident with increased biomass generation, especially in suboptimal condition using raw wastewater for co-cultures. These findings support a novel signaling mechanism originating from P. denitrificans that results in lipid accumulation in C. subellipsoidea and highlights an underexplored opportunity for an increased agroeconomic viability.

Oleaginous Microalga Coccomyxa subellipsoidea as a Highly Effective Cell Factory for CO2 Fixation and High-Protein Biomass Production by Optimal Supply of Inorganic Carbon and Nitrogen.

Microalgae used for CO2 biofixation can effectively relieve CO2 emissions and produce high-value biomass to achieve “waste-to-treasure” bioconversion. However, the low CO2 fixation efficiency and the restricted application of biomass are currently bottlenecks, limiting the economic viability of CO2 biofixation by microalgae. To achieve high-efficient CO2 fixation and high-protein biomass production, the oleaginous microalga Coccomyxa subellipsoidea (C. subellipsoidea) was cultivated autotrophically through optimizing inorganic carbon and nitrogen supply. 0.42 g L−1 NaHCO3 supplemented with 2% CO2 as a hybrid carbon source resulted in high biomass concentration (3.89 g L−1) and productivity (318.33) with CO2 fixation rate 544.21 mg L−1 d−1 in shake flasks. Then, used in a 5-L photo-fermenter, the maximal protein content (60.93% DW) in batch 1, and the highest CO2 fixation rate (1043.95 mg L−1 d−1) with protein content (58.48% DW) in batch 2 of repeated fed-batch cultures were achieved under 2.5 g L−1 nitrate. The relative expression of key genes involved in photosynthesis, glycolysis, and protein synthesis showed significant upregulation. This study developed a promising approach for enhancing carbon allocation to protein synthesis in oleaginous microalga, facilitating the bioconversion of the fixed carbon into algal protein instead of oil in green manufacturing.

Study of Biodiversity of Algae and Cyanobacteria of Mutnovsky and Gorely Volcanoes Soils (Kamchatka Peninsula) Using a Polyphasic Approach

Volcanic activity has a significant influence on the development of terrestrial ecosystems, including the Kamchatka Peninsula. We aimed to study the terrestrial algoflora of the Mutnovsky and Gorely volcanoes based on the use of clonal cultures of algae and cyanobacteria, and phenotypic and molecular genetic analyses. A total of 48 taxa were identified: 9 cyanobacteria, 32 Chlorophyta (11 Chlorophyceae, 21 Trebouxiophyceae), 3 Ochrophyta, and 4 Charophyta. In soils of the Mutnovsky volcano, 30 taxa were found, and in soils of the Gorely volcano, 24 were observed. In the studied area, small coccoid or mucilage-producing algae, which belong to cosmopolitan species, were identified, including representatives of the genera Bracteacoccus, Chlorococcum, Coccomyxa, Coelastrella, Klebsormidium, Neocystis, and Vischeria. Certain taxa were detected for the first time in the studied region, including Bracteacoccus bullatus, Chlorococcum hypnosporum, Chlorococcum lobatum, Coccomyxa subellipsoidea, Klebsormidium nitens, Leptosira obovata, Lobosphaera incisa, Parietochloris pseudoalveolaris, Stenomitos tremulus, and Vischeria magna. Our analysis of the algal communities at different altitudes reveals expansion in species richness with increasing distance from the tops of the volcanoes. The obtained data allowed us to estimate the real biodiversity of terrestrial algae and cyanobacteria of Kamchatkan volcanic soils, as well as the ecologies of these microorganisms.

The effect of temperature conditions during growth on the transformation frequency of Coccomyxa subellipsoidea C-169 obtained by electroporation

In this study, we have shown that transformation efficiency of Coccomyxa subellipsoidea C-169 obtained by electroporation can be significantly increased by either supra- or sub-optimal growth temperatures.

CsubMADS1, a lag phase transcription factor, controls development of polar eukaryotic microalga Coccomyxa subellipsoidea C-169.

MADS-box transcription factors (TFs) have not been functionally delineated in microalgae. In this study, the role of CsubMADS1 from microalga Coccomyxa subellipsoidea C-169 has been explored. Unlike Type II MADS-box proteins of seed plants with MADS, Intervening, K-box, and C domains, CsubMADS1 only has MADS and Intervening domains. It forms a group with MADS TFs from algae in the phylogenetic tree within the Type II MIKCC clade. CsubMADS1 is expressed strongly in the lag phase of growth. The CsubMADS1 monomer does not have a specific localization in the nucleus, and it forms homodimers to localize exclusively in the nucleus. The monomer has two nuclear localization signals (NLSs): an N-terminal NLS and an internal NLS. The internal NLS is functional, and the homodimer requires two NLSs for specific nuclear localization. Overexpression (OX) of CsubMADS1 slows down the growth of the culture and leads to the creation of giant polyploid multinucleate cells, resembling autospore mother cells. This implies that the release of autospores from autospore mother cells may be delayed. Thus, in wild-type (WT) cells, CsubMADS1 may play a crucial role in slowing down growth during the lag phase. Due to starvation in 2-month-old colonies on solid media, the WT colonies produce mucilage, whereas OX colonies produce significantly less mucilage. Thus, CsubMADS1 also negatively regulates stress-induced mucilage production and probably plays a role in stress tolerance during the lag phase. Taken together, our results reveal that CsubMADS1 is a key TF involved in the development and stress tolerance of this polar microalga.

Sterol Biosynthesis in Four Green Algae: A Bioinformatic Analysis of the Ergosterol Versus Phytosterol Decision Point.

Animals and fungi produce cholesterol and ergosterol, respectively, while plants produce the phytosterols stigmasterol, campesterol, and β‐sitosterol in various combinations. The recent sequencing of many algal genomes allows the detailed reconstruction of the sterol metabolic pathways. Here, we characterized sterol synthesis in two sequenced Chlorella spp., the free‐living C. sorokiniana, and symbiotic C. variabilis NC64A. Chlamydomonas reinhardtii was included as an internal control and Coccomyxa subellipsoidea as a plant‐like outlier. We found that ergosterol was the major sterol produced by Chlorella spp. and C. reinhardtii, while C. subellipsoidea produced the three phytosterols found in plants. In silico analysis of the C. variabilis NC64A, C. sorokiniana, and C. subellipsoidea genomes identified 22 homologs of sterol biosynthetic genes from Arabidopsis thaliana, Saccharomyces cerevisiae, and C. reinhardtii. The presence of CAS1, CPI1, and HYD1 in the four algal genomes suggests the higher plant cycloartenol branch for sterol biosynthesis, confirming that algae and fungi use different pathways for ergosterol synthesis. Phylogenetic analysis for 40 oxidosqualene cyclases (OSCs) showed that the nine algal OSCs clustered with the cycloartenol cyclases, rather than the lanosterol cyclases, with the OSC for C. subellipsoidea positioned in between the higher plants and the eight other algae. With regard to why C. subellipsoidea produced phytosterols instead of ergosterol, we identified 22 differentially conserved positions where C. subellipsoidea CAS and A. thaliana CAS1 have one amino acid while the three ergosterol producing algae have another. Together, these results emphasize the position of the unicellular algae as an evolutionary transition point for sterols.

Comparative genomics of Chlamydomonas.

Despite its role as a reference organism in the plant sciences, the green alga Chlamydomonas reinhardtii entirely lacks genomic resources from closely related species. We present highly contiguous and well-annotated genome assemblies for three unicellular C. reinhardtii relatives: Chlamydomonas incerta, Chlamydomonas schloesseri, and the more distantly related Edaphochlamys debaryana. The three Chlamydomonas genomes are highly syntenous with similar gene contents, although the 129.2 Mb C. incerta and 130.2 Mb C. schloesseri assemblies are more repeat-rich than the 111.1 Mb C. reinhardtii genome. We identify the major centromeric repeat in C. reinhardtii as a LINE transposable element homologous to Zepp (the centromeric repeat in Coccomyxa subellipsoidea) and infer that centromere locations and structure are likely conserved in C. incerta and C. schloesseri. We report extensive rearrangements, but limited gene turnover, between the minus mating type loci of these Chlamydomonas species. We produce an eight-species core-Reinhardtinia whole-genome alignment, which we use to identify several hundred false positive and missing genes in the C. reinhardtii annotation and >260,000 evolutionarily conserved elements in the C. reinhardtii genome. In summary, these resources will enable comparative genomics analyses for C. reinhardtii, significantly extending the analytical toolkit for this emerging model system.

Physiological and Molecular Alterations of Phycobionts of Genus Trebouxia and Coccomyxa Exposed to Cadmium.

Several studies on aeroterrestrial microalgae are unravelling their resistance mechanisms to different abiotic stressors, including hazardous metals, pointing to their future role as bioremediation microorganisms. In the present study, physiological and molecular alterations of four phycobionts of genus Trebouxia (T. TR1 and T. TR9) and Coccomyxa (C. subellipsoidea and C. simplex) exposed to Cd were studied. Cd accumulation and subcellular distribution, cell wall structure, production of biothiols (GSH and phytochelatins), reactive oxygen species (ROS) formation, expression of key antioxidant genes and ROS-related enzymes were evaluated to determine the physiological differences among the four microalgae, with the aim to identify the most suitable microorganism for further biotechnological applications. After 7 days of Cd exposure, Coccomyxa algae showed higher capacity of Cd intake than Trebouxia species, with C. subellipsoidea being the highest Cd accumulator at both intracellular and, especially, cell wall level. Cd induced ROS formation in the four microalgae, but to a greater extent in both Coccomyxa algae. Trebouxia TR9 showed the lowest Cd-dependent oxidative stress probably due to glutathione reductase induction. All microalgae synthetized phytochelatins in response to Cd but in a species-specific and a dose-dependent manner. Results from this study agree with the notion that each microalga has evolved a distinct strategy to detoxify hazardous metals like Cd and to cope with oxidative stress associated with them. Coccomyxa subellipsoidea and Trebouxia TR9 appear as the most interesting candidates for further applications.