Transcriptome analysis of the bloom-forming dinoflagellate Prorocentrum donghaiense exposed to Ginkgo biloba leaf extract, with an emphasis on photosynthesis.

Ginkgo biloba leaf extract (GBE) can effectively treat bloom-forming freshwater algae. However, there is limited information about the underlying suppression mechanism of the marine bloom-forming Prorocentrum donghaiense-the most dominant algal bloom species in the East China Sea. We investigated the effect of GBE on P. donghaiense in terms of its response to photosynthesis at the molecular/omic level. In total, 93,743 unigenes were annotated using six functional databases. Furthermore, 67,203 differentially expressed genes (DEGs) were identified in algae treated with 1.8 g∙L-1 GBE. Among these DEGs, we identified the genes involved in photosynthesis. PsbA, PsbB and PsbD in photosystem II, PsaA in photosystem I, and PetB and PetD in the cytochrome b6/f complex were downregulated. Other related genes, such as PsaC, PsaE, and PsaF in photosystem I; PetA in the cytochrome b6/f complex; and atpA, atpD, atpH, atpG, and atpE in the F-type H+-ATPase were upregulated. These results suggest that the structure and activity of the complexes were destroyed by GBE, thereby inhibiting the electron flow between the primary and secondary quinone electron acceptors, primary quinone electron acceptor, and oxygen-evolving complex in the PSII complex, and interrupting the electron flow between PSII and PSI, ultimately leading to a decline in algal cell photosynthesis. These findings provide a basis for understanding the molecular mechanisms underlying P. donghaiense exposure to GBE and a theoretical basis for the prevention and control of harmful algal blooms.

Transcriptome analysis reveals unique C4-like photosynthesis and oil body formation in an arachidonic acid-rich microalga Myrmecia incisa Reisigl H4301.

BACKGROUND: Arachidonic acid (ArA) is important for human health because it is one of the major components of mammalian brain membrane phospholipids. The interest in ArA inspired the search for a new sustainable source, and the green microalga Myrmecia incisa Reisigl H4301 has been found a potential ArA-producer due to a high content of intracellular ArA. To gain more molecular information about metabolism pathways, including the biosynthesis of ArA in the non-model microalga, a transcriptomic analysis was performed. RESULTS: The 454 pyrosequencing generated 371,740 high-quality reads, which were assembled into 51,908 unique sequences consisting of 22,749 contigs and 29,159 singletons. A total of 11,873 unique sequences were annotated through BLAST analysis, and 3,733 were assigned to Gene Ontology (GO) categories. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis uncovered a C4-like photosynthesis pathway in M. incisa. The biosynthesis pathways of lipid particularly those of ArA and triacylglycerol (TAG) were analyzed in detail, and TAG was proposed to be accumulated in oil bodies in the cytosol with the help of caleosin or oil globule-associated proteins. In addition, the carotenoid biosynthesis pathways are discussed. CONCLUSION: This transcriptomic analysis of M. incisa enabled a global understanding of mechanisms involved in photosynthesis, de novo biosynthesis of ArA, metabolism of carotenoids, and accumulation of TAG in M. incisa. These findings provided a molecular basis for the research and possibly economic exploitation of this ArA-rich microalga.

Nuclear-encoded CbbX located in chloroplast is essential for the activity of red-type Rubisco in Saccharina japonica.

Saccharina japonica (Laminariales, Phaeophyta) is a brown alga and the major component of algae beds on the northwest coast of the Pacific Ocean. Rubisco, the key enzyme of CO2 fixation in photosynthesis, is inhibited by nonproductive binding of its substrate RuBP and other sugar phosphates. The inhibited Rubisco in eukaryotic phytoplankton of the red plastid lineage was reactivated by CbbXs, the red-type Rubisco activases, through the process of ATP-hydrolysis-powered remodeling. As well documented, CbbXs had two types of subunits encoded by the plastid or nuclear genome respectively. In this study, both proteins of S. japonica (SjCbbX-n and SjCbbX-p) were localized in the chloroplast illustrated by immuno-electron microscopy technique. GST pull-down detection verified SjCbbX-n could interact with SjCbbX-p. Two-dimensional electrophoresis-based Western blot analysis illustrated that the endogenous SjCbbXs could form heterohexamer in the ratio of 1:1. Activase activity assays showed that although both the recombinant proteins of SjCbbXs were functional, SjCbbX-n illustrated the significantly higher activase activity than SjCbbX-p. Notably, when the two proteins were mixed, the highest specific efficiencies of Rubisco were obtained. These results implied SjCbbX-n may be essential for Rubisco activation. Molecular evolutionary analysis of cbbx genes revealed that cbbx-n originated from the duplication of cbbx-p and then evolved independently under the positive selection pressure. This is the first report about the functional relationship between the two types of CbbXs in macroalge with the red-type Rubisco and provides useful information for revealing the mechanism of high photosynthetic efficiency of this important kelp.

pH-responsive magnetic artificial melanin with tunable aggregation-induced stronger magnetism for rapid remediation of plastic fragments.

The global occurrence of plastic fragment pollutants in water resources has raised concerns about food safety, drinking water security, and long-term ecological impacts worldwide. The different chemical nature, the persistence, and the smaller size make micro-plastics accumulators for toxins that pose a potential threat to human health. Generally, the smaller the size of the plastic fragments is, the more difficult it is to remove them from the aquatic environment. Methods to remove plastics from water or other media are highly needed. Here, we develop core-shell superparamagnetic melanin nanoparticles, which can put magnetism on nano-/micro-plastics within 30 s and then rapidly remove them from water by applying an external magnetic field. The shell material (artificial nano-melanin) provides simultaneously attractive electrostatic, hydrophobic interaction, and van der Waals' forces to attract nano-/micro-plastics, which plays a key role in the rapid remediation of the plastic fragments. With this principle applied to a simple method, the average removal efficiency achieves 89.3%. We show a method for high-throughput remediation of various micro-plastics with simple materials and processes, which have the potential for rapid, green, and large-scale remediation in the future.

Genetic diversity and population structure analysis of Lateolabrax maculatus from Chinese coastal waters using polymorphic microsatellite markers.

In order to provide valuable guidelines for the conservation of germplasm of Lateolabrax maculatus, the genetic diversity and population structure analysis were evaluated for eight geographic populations along coastal regions of China, using 11 microsatellite DNA markers. The genetic parameters obtained showed that, eight populations can be clustered into two groups, the Northern group and the Southern group, concordant with their geographical positions. The UPGMA tree constructed according to the Nei's genetic distance along with the structure analysis and discriminant analysis of principal component also supported this result. This might be explained by the geographic separation and the divergent environmental conditions among the populations. It's worth noting that, QD (Qingdao) population from northern area was assigned to the Southern group and showed a close genetic relationship and similar genetic constitution with the southern populations. We speculated that large scales of anthropogenic transportation of wild fries from QD populations to the southern aquaculture areas in history should be the primary cause. The populations from GY (Ganyu), RD (Rudong) and BH (Binhai) had higher genetic diversity and showed limited genetic exchange with other populations, indicating better conservation of the natural resources in these regions. All populations were indicated to have experienced bottleneck events in history.

Changes in community structure and photosynthetic activities of total phytoplankton species during the growth, maintenance, and dissipation phases of a Prorocentrum donghaiense bloom.

The potential interactions between the bloom-forming dinoflagellates and other phytoplankton during the algal bloom cycle are interesting, while the causes for the phytoplankton community changes were not fully understood. We hypothesized that phytoplankton community structure and photosynthetic activities of total phytoplankton have their special characteristics in different phases of the algal blooms. To test this hypothesis, a survey covering the process of a Prorocentrum donghaiense bloom in coastal waters between Dongtou and Nanji Islands was carried out from 9 to 20 May 2016, and the changes in the phytoplankton community and photosynthetic activities of total phytoplankton were determined. Surface seawater was sampled for microscopic analysis of phytoplankton composition and pulse amplitude modulated (PAM) chlorophyll fluorescence analysis of photosynthetic activities of the total phytoplankton species. A total of 25, 31, and 19 phytoplankton species were identified in its growth (9-12 May), maintenance (13-18 May) and dissipation phases (19-20 May), respectively. Diatoms were dominant in terms of species number while dinoflagellates were predominant at cell abundance. Dinoflagellates were the major dominant species during three phases of the bloom based on the dominance (Y) value, whereas the dominant species extended to dinoflagellates and diatoms including P. donghaiense, Coscinodiscus argus, Gonyaulax spinifera, Cyclotella sp. and Scrippsiella trochoidea in the dissipation phase. In the maintenance phase, the average cell abundances of the total phytoplankton and P. donghaiense were consistent with the chlorophyll a (Chla) concentration in the seawater; for the diversity indices of total phytoplankton species, Simpson index (C) was the highest while Shannon index (H') and Pielou evenness index (J') were the lowest. Furthermore, photosynthetic activities of the total phytoplankton species represented by the effective quantum yield (Fq'/Fm') and the maximum relative electron transport rate (rETRmax) in the maintenance phase were higher than those in the growth and dissipation phases. The results indicated that the characteristics of phytoplankton community structure and photosynthetic activities could be regarded as criteria in predicting the phases of algal blooms.

Complete mitochondrial genome analysis of Japanese Spanish mackerel (Scomberomorus niphonius) with phylogenetic consideration.

The complete mitochondrial DNA (mtDNA) of Japanese Spanish mackerel (Scomberomorus niphonius) was cloned and sequenced. The total length of the mitochondrial genome is 16,646 bp with an accession number KY228987. Thirty-seven genes are identified in total, including 13 protein-coding genes, 22 transfer RNA (tRNA) genes, 2 ribosomal RNA (rRNA) genes and a putative D-loop region. Among these genes, 9 are encoded on the light strand, while others are encoded on the heavy strand. The overall base composition of mitogenome is 28.39% for A, 16.14% for G, 26.52% for T, 28.96% for C, respectively, with a slight higher A + T content (54.91%). The phylogeny analysis based on 18 COI amino acid sequences suggested that S. niphonius and the other two species from Scomberomorus (Scombridae) formed a cluster apart from the one comprising other genus from Scombridae. The complete mitogenome may shed light on the future study of genetic mechanism of Scomberomorus niphonius.

Phospholipid: diacylglycerol acyltransferase contributes to the conversion of membrane lipids into triacylglycerol in Myrmecia incisa during the nitrogen starvation stress.

In addition to the Kennedy pathway for de novo biosynthesis, triacylglycerol (TAG), the most important stock for microalgae-based biodiesel production, can be synthesized by phospholipid: diacylglycerol acyltransferase (PDAT) that transfers an acyl group from phospholipids (PLs) to diacylglycerol (DAG). This study presents a novel gene that encodes PDAT from the green microalga Myrmecia incisa Reisigl H4301 (designated MiPDAT ). MiPDAT is localized on the plasma membrane (PM) via the agroinfiltration of tobacco leaves with a green fluorescent protein-fused construct. MiPDAT synthesizes TAG based on functional complementary experiments in the mutant yeast strain H1246 and the membrane lipid phosphatidylcholine (PC) is preferentially used as substrates as revealed by in vitro enzyme activity assay. The gradually increased transcription levels of MiPDAT in M. incisa during the cultivation under nitrogen starvation conditions is proposed to be responsible for the decrease and increase of the PC and TAG levels, respectively, as detected by liquid chromatography-mass spectrometry after 4 d of nitrogen starvation. In addition, the mechanism by which MiPDAT in this microalga uses PC to yield TAG is discussed. Accordingly, it is concluded that this PM-located PDAT contributes to the conversion of membrane lipids into TAG in M. incisa during the nitrogen starvation stress.

Site-Directed Mutagenesis from Arg195 to His of a Microalgal Putatively Chloroplastidial Glycerol-3-Phosphate Acyltransferase Causes an Increase in Phospholipid Levels in Yeast.

To analyze the contribution of glycerol-3-phosphate acyltransferase (GPAT) to the first acylation of glycerol-3-phosphate (G-3-P), the present study focused on a functional analysis of the GPAT gene from Lobosphaera incisa (designated as LiGPAT). A full-length cDNA of LiGPAT consisting of a 1,305-bp ORF, a 1,652-bp 5'-UTR, and a 354-bp 3'-UTR, was cloned. The ORF encoded a 434-amino acid peptide, of which 63 residues at the N-terminus defined a chloroplast transit peptide. Multiple sequence alignment and phylogeny analysis of GPAT homologs provided the convincible bioinformatics evidence that LiGPAT was localized to chloroplasts. Considering the conservation of His among the G-3-P binding sites from chloroplastidial GPATs and the substitution of His by Arg at position 195 in the LiGPAT mature protein (designated mLiGPAT), we established the heterologous expression of either mLiGPAT or its mutant (Arg195His) (sdmLiGPAT) in the GPAT-deficient yeast mutant gat1Δ. Lipid profile analyses of these transgenic yeasts not only validated the acylation function of LiGPAT but also indicated that the site-directed mutagenesis from Arg(195) to His led to an increase in the phospholipid level in yeast. Semi-quantitative analysis of mLiGPAT and sdmLiGPAT, together with the structural superimposition of their G-3-P binding sites, indicated that the increased enzymatic activity was caused by the enlarged accessible surface of the phosphate group binding pocket when Arg(195) was mutated to His. Thus, the potential of genetic manipulation of GPAT to increase the glycerolipid level in L. incisa and other microalgae would be of great interest.