Choline Dehydrogenase Contributes to Salt Tolerance in Dunaliella through Betaine Synthesis.

In Dunaliella tertiolecta, a microalga renowned for its extraordinary tolerance to high salinity levels up to 4.5 M NaCl, the mechanisms underlying its stress response have largely remained a mystery. In a groundbreaking discovery, this study identifies a choline dehydrogenase enzyme, termed DtCHDH, capable of converting choline to betaine aldehyde. Remarkably, this is the first identification of such an enzyme not just in D. tertiolecta but across the entire Chlorophyta. A 3D model of DtCHDH was constructed, and molecular docking with choline was performed, revealing a potential binding site for the substrate. The enzyme was heterologously expressed in E. coli Rosetta (DE3) and subsequently purified, achieving enzyme activity of 672.2 U/mg. To elucidate the role of DtCHDH in the salt tolerance of D. tertiolecta, RNAi was employed to knock down DtCHDH gene expression. The results indicated that the Ri-12 strain exhibited compromised growth under both high and low salt conditions, along with consistent levels of DtCHDH gene expression and betaine content. Additionally, fatty acid analysis indicated that DtCHDH might also be a FAPs enzyme, catalyzing reactions with decarboxylase activity. This study not only illuminates the role of choline metabolism in D. tertiolecta's adaptation to high salinity but also identifies a novel target for enhancing the NaCl tolerance of microalgae in biotechnological applications.

Phylogenetic and functional diversity of aldehyde-alcohol dehydrogenases in microalgae.

KEY MESSAGE: The study shows the biochemical and enzymatic divergence between the two aldehyde-alcohol dehydrogenases of the alga Polytomella sp., shedding light on novel aspects of the enzyme evolution amid unicellular eukaryotes. Aldehyde-alcohol dehydrogenases (ADHEs) are large metalloenzymes that typically perform the two-step reduction of acetyl-CoA into ethanol. These enzymes consist of an N-terminal acetylating aldehyde dehydrogenase domain (ALDH) and a C-terminal alcohol dehydrogenase (ADH) domain. ADHEs are present in various bacterial phyla as well as in some unicellular eukaryotes. Here we focus on ADHEs in microalgae, a diverse and polyphyletic group of plastid-bearing unicellular eukaryotes. Genome survey shows the uneven distribution of the ADHE gene among free-living algae, and the presence of two distinct genes in various species. We show that the non-photosynthetic Chlorophyte alga Polytomella sp. SAG 198.80 harbors two genes for ADHE-like enzymes with divergent C-terminal ADH domains. Immunoblots indicate that both ADHEs accumulate in Polytomella cells growing aerobically on acetate or ethanol. ADHE1 of ~ 105-kDa is found in particulate fractions, whereas ADHE2 of ~ 95-kDa is mostly soluble. The study of the recombinant enzymes revealed that ADHE1 has both the ALDH and ADH activities, while ADHE2 has only the ALDH activity. Phylogeny shows that the divergence occurred close to the root of the Polytomella genus within a clade formed by the majority of the Chlorophyte ADHE sequences, next to the cyanobacterial clade. The potential diversification of function in Polytomella spp. unveiled here likely took place after the loss of photosynthesis. Overall, our study provides a glimpse at the complex evolutionary history of the ADHE in microalgae which includes (i) acquisition via different gene donors, (ii) gene duplication and (iii) independent evolution of one of the two enzymatic domains.

Electrogenesis in Plasma Membrane Fraction of Halotolerant Microalga Dunaliella maritima and Effects of N,N'-Dicyclohexylcarbodiimide.

The effects of N,N'-dicyclohexylcarbodiimide (DCCD), non-specific inhibitor of various transport systems functioning in biological membranes, on Na+-transporting P-type ATPase of the green halotolerant microalga Dunaliella maritima were studied in the experiments with vesicular plasma membranes isolated from the alga cells. The effects of DCCD on electrogenic/ion transport function of the enzyme and its ATP hydrolase activity were investigated. Electrogenic/ion transport function of the enzyme was recorded as a Na+-dependent generation of electric potential on the vesicle membranes with the help of the potential-sensitive probe oxonol VI. It was found that unlike many other ion-transporting ATPases, the Na+-ATPase of D. maritima is insensitive to DCCD. This agent did not inhibit either ATP hydrolysis catalyzed by this enzyme or its transport activity. At the same time DCCD affected the ability of the vesicle membranes to maintain electric potential generated by the D. maritima Na+-ATPase. The observed effects can be explained based on the assumption that DCCD interacts with the Na+/H+ antiporter in the plasma membrane of D. maritima.

Kinetic improvement of an algal diacylglycerol acyltransferase 1 via fusion with an acyl-CoA binding protein.

Microalgal oils in the form of triacylglycerols (TAGs) are broadly used as nutritional supplements and biofuels. Diacylglycerol acyltransferase (DGAT) catalyzes the final step of acyl-CoA-dependent biosynthesis of TAG, and is considered a key target for manipulating oil production. Although a growing number of DGAT1s have been identified and over-expressed in some algal species, the detailed structure-function relationship, as well as the improvement of DGAT1 performance via protein engineering, remain largely untapped. Here, we explored the structure-function features of the hydrophilic N-terminal domain of DGAT1 from the green microalga Chromochloris zofingiensis (CzDGAT1). The results indicated that the N-terminal domain of CzDGAT1 was less disordered than those of the higher eukaryotic enzymes and its partial truncation or complete removal could substantially decrease enzyme activity, suggesting its possible role in maintaining enzyme performance. Although the N-terminal domains of animal and plant DGAT1s were previously found to bind acyl-CoAs, replacement of CzDGAT1 N-terminus by an acyl-CoA binding protein (ACBP) could not restore enzyme activity. Interestingly, the fusion of ACBP to the N-terminus of the full-length CzDGAT1 could enhance the enzyme affinity for acyl-CoAs and augment protein accumulation levels, which ultimately drove oil accumulation in yeast cells and tobacco leaves to higher levels than the full-length CzDGAT1. Overall, our findings unravel the distinct features of the N-terminus of algal DGAT1 and provide a strategy to engineer enhanced performance in DGAT1 via protein fusion, which may open a vista in generating improved membrane-bound acyl-CoA-dependent enzymes and boosting oil biosynthesis in plants and oleaginous microorganisms.

Expression of P-Type ATPases of Marine Green Microalga Dunaliella maritima under Hyperosmotic Salt Shock.

Partial sequences of P-type ATPases were cloned from the marine microalgae Dunaliella maritima, two putative H+-ATPases (DmHA1 and DmHA2) and two putative Ca2+-ATPases (DmCA1 and DmCA2). The probable functions of the cloned proteins were suggested on the basis of their primary structure similarity with the proteins whose functions have been already characterized. The transcriptional response of the cloned D. maritima ATPase genes to a sharp increase in the NaCl concentration in the culture medium (from 100 to 500 mM) was investigated by quantitative RT-PCR. Hyperosmotic salt shock led to a significant increase in the DmHA2 expression and to a slight increase in the DmCA2 expression, whereas the expression of the two other ATPases, DmHA1 and DmCA1, was decreased. These data indicate that the DmHA2 ATPase is involved in maintenance of ion homeostasis in D. maritima cells under hyperosmotic salt shock.

Interaction between 1,2-benzisothiazol-3(2H)-one and microalgae: Growth inhibition and detoxification mechanism.

Isothiazolinones, such as 1,2-benzisothiazol-3(2H)-one (BIT), are widely used as biocides for bacterial growth control in many domestic and industrial processes. Despite their advantages as biocides, they are highly toxic and pose a potential risk to the environment. This study investigated the inhibition process and detoxification mechanism involved in microalgal survival and growth recovery after BIT poisoning. BIT could seriously inhibit the growth of Scenedesmus sp. LX1, Chlorella sp. HQ, and Chlamydomonas reinhardtii with half maximal effective concentrations at 72 h (72h-EC50) of 1.70, 0.41, and 1.16 mg/L, respectively. The primary inhibition mechanism was the BIT-induced damage to microalgal photosynthetic systems. However, the inhibited strains could recover when their growth was not completely inhibited. The influence of this inhibiting effect on subsequent algal regrowth was negligible or weak. BIT consumption was the primary reason for their recovery. Notably, algae did not die even if their growth was completely inhibited. If the BIT concentration did not exceed a certain high level, then the inhibited algae could recover their growth relatively well. Microalgal generation of reduced glutathione (GSH) and the oxygen radical scavenging enzymes, superoxide dismutase (SOD) and catalase (CAT), played a key role in detoxification against BIT poisoning.

Functional assessment of plant and microalgal lipid pathway genes in yeast to enhance microbial industrial oil production.

As promising alternatives to fossil-derived oils, microbial lipids are important as industrial feedstocks for biofuels and oleochemicals. Our broad aim is to increase lipid content in oleaginous yeast through expression of lipid accumulation genes and use Saccharomyces cerevisiae to functionally assess genes obtained from oil-producing plants and microalgae. Lipid accumulation genes DGAT (diacylglycerol acyltransferase), PDAT (phospholipid: diacylglycerol acyltransferase), and ROD1 (phosphatidylcholine: diacylglycerol choline-phosphotransferase) were separately expressed in yeast and lipid production measured by fluorescence, solvent extraction, thin layer chromatography, and gas chromatography (GC) of fatty acid methyl esters. Expression of DGAT1 from Arabidopsis thaliana effectively increased total fatty acids by 1.81-fold above control, and ROD1 led to increased unsaturated fatty acid content of yeast lipid. The functional assessment approach enabled the fast selection of candidate genes for metabolic engineering of yeast for production of lipid feedstocks.

Accelerated triacylglycerol production and altered fatty acid composition in oleaginous microalga Neochloris oleoabundans by overexpression of diacylglycerol acyltransferase 2.

BACKGROUND: Microalgae are promising sources of lipid triacylglycerol (TAG) for biodiesel production. However, to date, microalgal biodiesel is technically feasible, but not yet economically viable. Increasing TAG content and productivity are important to achieve economic viability of microalgal biodiesel. To increase TAG content, oleaginous microalga Neochloris oleoabundans was genetically engineered with an endogenous key enzyme diacylglycerol acyltransferase 2 (NeoDGAT2) responsible for TAG biosynthesis. RESULTS: The integration of NeoDGAT2 expression cassettes in N. oleoabundans transformant was confirmed by PCR. The neutral lipid accumulation in the transformant detected by Nile red staining was accelerated and 1.9-fold higher than in wild type; the lipid bodies in the transformant visualized under fluorescence microscope were also larger. The NeoDGAT2 transcript was two-fold higher in the transformant than wild type. Remarkably higher lipid accumulation was found in the transformant than wild type: total lipid content increased 1.6-to 2.3-fold up to 74.5 ± 4.0% dry cell weight (DCW) and total lipid productivity increased 1.6- to 3.2-fold up to 14.6 ± 2.0 mg/L/day; while TAG content increased 1.8- to 3.2-fold up to 46.1 ± 1.6% DCW and TAG productivity increased 1.6- to 4.3-fold up to 8.9 ± 1.3 mg/L/day. A significantly altered fatty acid composition was detected in the transformant compared to wild type; the levels of saturated fatty acid C16:0 increased double to 49%, whereas C18:0 was reduced triple to 6%. Long-term stability was observed in the transformant continuously maintained in solid medium over 100 generations in a period of about 4 years. CONCLUSIONS: Our results demonstrate the increased TAG content and productivity in N. oleoabundans by NeoDGAT2 overexpression that may offer the first step towards making microalgae an economically feasible source for biodiesel production. The strategy for genetically improved microalga presented in this study can be applied to other microalgal species possessing desired characteristics for industrial biofuel production.

Phytochelatin synthesis in Dunaliella salina induced by arsenite and arsenate under various phosphate regimes.

This study investigated the dynamic variations in thiol compounds, including cysteine (Cys), glutathione (GSH), and phytochelatins (PCs), in Dunaliella salina samples exposed to arsenite [As(III)] and arsenate [As(V)] under various phosphate (PO43-) regimes. Our results showed that GSH was the major non-protein sulfhydryl compound in D. salina cells. As(III) and As(V) induced PC syntheses in D. salina. PC2, PC3, and PC4 were all found in algal cells; the PC concentrations decreased gradually while exposed to As for 3 d. The synthesis of PC2-3 was significantly affected by As(III) and As(V) concentrations in the cultures. More PCs were detected in the As(V)-treated algal cells compared with the As(III) treatment. PC levels increased with As(III)/As(V) amount in the medium, but remained stable after 112µgL-1 As(V) exposure. In contrast, significant (p<0.001) positive correlations were observed between PC synthesis and intracellular As(III) content or As accumulation in As(III)-treated algal cells during the 72-h exposure. PO43- had a significant influence on the PC synthesis in algal cells, irrespective of the As-treated species. Reductions in As uptake and subsequent PC synthesis by D. salina were observed as the PO43- concentration in the growth medium increased. L-Buthionine sulfoximine (BSO) differentially influenced PC synthesis in As-treated D. salina under different extracellular PO43- regimes. Overall, our data demonstrated that the production of GSH and PCs was affected by PO43- and that these thiols played an important role in As detoxification by D. salina.

Redox regulation of ATP sulfurylase in microalgae.

ATP sulfurylase (ATPS) catalyzes the first step of sulfur assimilation in photosynthetic organisms. An ATPS type A is mostly present in freshwater cyanobacteria, with four conserved cysteine residues. Oceanic cyanobacteria and most eukaryotic algae instead, possess an ATPS-B containing seven to ten cysteines; five of them are conserved, but only one in the same position as ATPS-A. We investigated the role of cysteines on the regulation of the different algal enzymes. We found that the activity of ATPS-B from four different microorganisms was enhanced when reduced and decreased when oxidized. The LC-MS/MS analysis of the ATPS-B from the marine diatom Thalassiosira pseudonana showed that the residue Cys-247 was presumably involved in the redox regulation. The absence of this residue in the ATPS-A of the freshwater cyanobacterium Synechocystis sp. instead, was consistent with its lack of regulation. Some other conserved cysteine residues in the ATPS from T. pseduonana and not in Synechocystis sp.were accessible to redox agents and possibly play a role in the enzyme regulation. Furthermore, the fact that oceanic cyanobacteria have ATPS-B structurally and functionally closer to that from most of eukaryotic algae than to the ATPS-A from other cyanobacteria suggests that life in the sea or freshwater may have driven the evolution of ATPS.

Energy cost of intracellular metal and metalloid detoxification in wild-type eukaryotic phytoplankton.

Microalgae use various cellular mechanisms to detoxify both non-essential and excess essential metals or metalloids. There exists however, a threshold in intracellular metal(loid) concentrations beyond which detoxification mechanisms are no longer effective and inhibition of cell division inevitably occurs. It is therefore important to determine whether the availability of energy in the cell could constrain metal(loid) detoxification capacity and to better define the thresholds beyond which a metal(loid) becomes toxic. To do this we performed the first extensive bioenergetics analysis of intracellular metal(loid) detoxification mechanisms (e.g., metal-binding peptides, polyphosphate granules, metal efflux, metal and metalloid reduction, metalloid methylation, enzymatic and non-enzymatic antioxidants) in wild-type eukaryotic phytoplankton based on the biochemical mechanisms of each detoxification strategy and on experimental measurements of detoxifying biomolecules in the literature. The results show that at the onset of metal(loid) toxicity to growth, all the detoxification strategies considered required only a small fraction of the total cellular energy available for growth indicating that intracellular detoxification ability in wild-type eukaryotic phytoplankton species is not constrained by the availability of cellular energy. The present study brings new insights into metal(loid) toxicity mechanisms and detoxification strategies in wild-type eukaryotic phytoplankton.

Nickel has biochemical, physiological, and structural effects on the green microalga Ankistrodesmus falcatus: An integrative study.

In recent years, the release of chemical pollutants to water bodies has increased due to anthropogenic activities. Ni(2+) is an essential metal that causes damage to aquatic biota at high concentrations. Phytoplankton are photosynthesizing microscopic organisms that constitute a fundamental community in aquatic environments because they are primary producers that sustain the aquatic food web. Nickel toxicity has not been characterized in all of the affected levels of biological organization. For this reason, the present study evaluated the toxic effects of nickel on the growth of a primary producer, the green microalga Ankistrodesmus falcatus, and on its biochemical, enzymatic, and structural levels. The IC50 (96h) was determined for Ni(2+). Based on this result, five concentrations were determined for additional tests, in which cell density was evaluated daily. At the end of the assay, pigments and six biomarkers, including antioxidant enzymes (catalase [CAT], glutathione peroxidase [GPx], superoxide dismutase [SOD]), and macromolecules (proteins, carbohydrates and lipids), were quantified; the integrated biomarker response (IBR) was determined also. The microalgae were observed by SEM and TEM. Population growth was affected starting at 7.5 µg L(-1) (0.028 µM), and at 120 µg L(-1) (0.450 µM), growth was inhibited completely; the determined IC50 was 17 µg L(-1). Exposure to nickel reduced the concentration of pigments, decreased the content of all of the macromolecules, inhibited of SOD activity, and increased CAT and GPx activities. The IBR revealed that Ni(2+) increased the antioxidant response and diminished the macromolecules concentration. A. falcatus was affected by nickel at very low concentrations; negative effects were observed at the macromolecular, enzymatic, cytoplasmic, and morphological levels, as well as in population growth. Ni(2+) toxicity could result in environmental impacts with consequences on the entire aquatic community. Current regulations should be revised to protect primary producers.

Cyclobutane pyrimidine dimers photolyase from extremophilic microalga: remarkable UVB resistance and efficient DNA damage repair.

Bacteria living in the Antarctic region have developed several adaptive features for growth and survival under extreme conditions. Chlamydomonas sp. ICE-Lis well adapted to high levels of solar UV radiation. A putative photolyase was identified in the Chlamydomonas sp. ICE-L transcriptome. The complete cDNA sequence was obtained by RACE-PCR. This PHR encoding includes a polypeptide of 579 amino acids with clear photolyase signatures belonging to class II CPD-photolyases, sharing a high degree of homology with Chlamydomonas reinhardtii (68%). Real-time PCR was performed to investigate the potential DNA damage and responses following UVB exposure. CPD photolyase mRNA expression level increased over 50-fold in response to UVB radiation for 6h. Using photolyase complementation assay, we demonstrated that DNA photolyase increased photo-repair more than 116-fold in Escherichia coli strain SY2 under 100µw/cm(2) UVB radiation. To determine whether photolyase is active in vitro, CPD photolyase was over-expressed. It was shown that pyrimidine dimers were split by the action of PHR2. This study reports the unique structure and high activity of the enzyme. These findings are relevant for further understanding of molecular mechanisms of photo-reactivation, and will accelerate the utilization of photolyase in the medical field.

Chloroplast-targeting protein expression in the oleaginous diatom Fistulifera solaris JPCC DA0580 toward metabolic engineering.

The chloroplast plays critical roles in lipid metabolism of microalgae, thus it is recognized as an attractive target of metabolic engineering to enhance biofuel production. It has been well known that recombinant protein expression in microalgal chloroplasts needs specific signal sequence which governs the transition manner of nuclear-encoded polypeptides within the subcellular compartments. However certain microalgae, including diatoms, have complex membrane systems surrounding the chloroplast, and thus chloroplast-targeting protein expression with the signal sequence has rarely been demonstrated except for a few model non-oleaginous diatoms. In this study, we performed recombinant green fluorescence protein (GFP) expression and transportation into the chloroplast of the oleaginous marine diatom, Fistulifera solaris JPCC DA0580. The signal sequence of ATP synthetase gamma subunit, which was predicted to localize in the chloroplast according to a bioinformatics analysis pipeline, was employed as a key factor of this technique. As a result, specific localization of GFP in the chloroplast was observed. It would be useful to engineer the lipid synthesis pathways existing in the chloroplast. Furthermore, intensive gathering of GFP in the rod-like structure was also detected, which has not been observed in model diatom studies. As comparing with electron microscopic observation, the structure was estimated to be a pyrenoid.

Unraveling vitamin B12-responsive gene regulation in algae.

Photosynthetic microalgae play a vital role in primary productivity and biogeochemical cycling in both marine and freshwater systems across the globe. However, the growth of these cosmopolitan organisms depends on the bioavailability of nutrients such as vitamins. Approximately one-half of all microalgal species requires vitamin B12 as a growth supplement. The major determinant of algal B12 requirements is defined by the isoform of methionine synthase possessed by an alga, such that the presence of the B12-independent methionine synthase (METE) enables growth without this vitamin. Moreover, the widespread but phylogenetically unrelated distribution of B12 auxotrophy across the algal lineages suggests that the METE gene has been lost multiple times in evolution. Given that METE expression is repressed by the presence of B12, prolonged repression by a reliable source of the vitamin could lead to the accumulation of mutations and eventually gene loss. Here, we probe METE gene regulation by B12 and methionine/folate cycle metabolites in both marine and freshwater microalgal species. In addition, we identify a B12-responsive element of Chlamydomonas reinhardtii METE using a reporter gene approach. We show that complete repression of the reporter occurs via a region spanning -574 to -90 bp upstream of the METE start codon. A proteomics study reveals that two other genes (S-Adenosylhomocysteine hydrolase and Serine hydroxymethyltransferase2) involved in the methionine-folate cycle are also repressed by B12 in C. reinhardtii. The strong repressible nature and high sensitivity of the B12-responsive element has promising biotechnological applications as a cost-effective regulatory gene expression tool.

Management of oxidative stress by microalgae.

The aim of this review is to provide an overview of the current research on oxidative stress in eukaryotic microalgae and the antioxidant compounds microalgae utilize to control oxidative stress. With the potential to exploit microalgae for the large-scale production of antioxidants, interest in how microalgae manage oxidative stress is growing. Microalgae can experience increased levels of oxidative stress and toxicity as a result of environmental conditions, metals, and chemicals. The defence mechanisms for microalgae include antioxidant enzymes such as superoxide dismutase, catalase, peroxidases, and glutathione reductase, as well as non-enzymatic antioxidant molecules such as phytochelatins, pigments, polysaccharides, and polyphenols. Discussed herein are the 3 areas the literature has focused on, including how conditions stress microalgae and how microalgae respond to oxidative stress by managing reactive oxygen species. The third area is how beneficial microalgae antioxidants are when administered to cancerous mammalian cells or to rodents experiencing oxidative stress.

A comparative study of iron uptake mechanisms in marine microalgae: iron binding at the cell surface is a critical step.

We investigated iron uptake mechanisms in five marine microalgae from different ecologically important phyla: the diatoms Phaeodactylum tricornutum and Thalassiosira pseudonana, the prasinophyceae Ostreococcus tauri and Micromonas pusilla, and the coccolithophore Emiliania huxleyi. Among these species, only the two diatoms were clearly able to reduce iron, via an inducible (P. tricornutum) or constitutive (T. pseudonana) ferrireductase system displaying characteristics similar to the yeast (Saccharomyces cerevisiae) flavohemoproteins proteins. Iron uptake mechanisms probably involve very different components according to the species, but the species we studied shared common features. Regardless of the presence and/or induction of a ferrireductase system, all the species were able to take up both ferric and ferrous iron, and iron reduction was not a prerequisite for uptake. Iron uptake decreased with increasing the affinity constants of iron-ligand complexes and with increasing ligand-iron ratios. Therefore, at least one step of the iron uptake mechanism involves a thermodynamically controlled process. Another step escapes to simple thermodynamic rules and involves specific and strong binding of ferric as well as ferrous iron at the cell surface before uptake of iron. Binding was paradoxically increased in iron-rich conditions, whereas uptake per se was induced in all species only after prolonged iron deprivation. We sought cell proteins loaded with iron following iron uptake. One such protein in O. tauri may be ferritin, and in P. tricornutum, Isip1 may be involved. We conclude that the species we studied have uptake systems for both ferric and ferrous iron, both involving specific iron binding at the cell surface.

De novo transcriptomic analysis of an oleaginous microalga: pathway description and gene discovery for production of next-generation biofuels.

BACKGROUND: Eustigmatos cf. polyphem is a yellow-green unicellular soil microalga belonging to the eustimatophyte with high biomass and considerable production of triacylglycerols (TAGs) for biofuels, which is thus referred to as an oleaginous microalga. The paucity of microalgae genome sequences, however, limits development of gene-based biofuel feedstock optimization studies. Here we describe the sequencing and de novo transcriptome assembly for a non-model microalgae species, E. cf. polyphem, and identify pathways and genes of importance related to biofuel production. RESULTS: We performed the de novo assembly of E. cf. polyphem transcriptome using Illumina paired-end sequencing technology. In a single run, we produced 29,199,432 sequencing reads corresponding to 2.33 Gb total nucleotides. These reads were assembled into 75,632 unigenes with a mean size of 503 bp and an N50 of 663 bp, ranging from 100 bp to >3,000 bp. Assembled unigenes were subjected to BLAST similarity searches and annotated with Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) orthology identifiers. These analyses identified the majority of carbohydrate, fatty acids, TAG and carotenoids biosynthesis and catabolism pathways in E. cf. polyphem. CONCLUSIONS: Our data provides the construction of metabolic pathways involved in the biosynthesis and catabolism of carbohydrate, fatty acids, TAG and carotenoids in E. cf. polyphem and provides a foundation for the molecular genetics and functional genomics required to direct metabolic engineering efforts that seek to enhance the quantity and character of microalgae-based biofuel feedstock.

Chemical composition of volatile oil from Artemisia ordosica and its allelopathic effects on desert soil microalgae, Palmellococcus miniatus.

Plants have been used to restore vegetation in desert region in Shapotou, where naturally biological soil crusts (BSCs) have formed after planting for several years. However, few works have been done on the allelopathic effects between the plants and soil microalgae in BSCs currently. In this study, we investigated the chemical compositions of volatile oil of Artemisia ordosica and its allelopathic effects on photosynthetic system II (PSII) and antioxidant system of Palmellococcus miniatus, a green algae isolated from BSCs. 37 components, consisted of 17 terpenoids, 14 alcohols, 2 esters, 2 ketones and other 2 components were identified in the volatile oil from A. ordosica by GC-MS analysis. High concentration of volatile oil could significantly inhibit the growth and photosynthetic activity (Fv/Fm), and decreased the photosynthetic parameters by affecting photon absorption, electron transport and the reaction center of PSII of P. miniatus, and also cause the significant increase of superoxide dismutase (SOD; EC 1.15.1.) activity, peroxidase (POD; EC 1.11.1.7) activity, reactive oxygen evolution (ROS) and malondialdehyde (MDA) contents of P. miniatus through the combined effects of components in volatile oil. The results indicated that the emission of volatile oil of A. ordosica could inhibit the growth, photosynthesis of P. miniatus through the oxidative damage, and thus might negatively affect the development of BSCs.