BackgroundPhotosynthetic oleaginous microalgae are promising feedstocks for biofuels. Acyl-CoA:diacylglycerol acyltransferases (DGATs) represent rich sources for engineering microalgal lipid production. The principal activity of DGATs has been defined as a single-function enzyme catalyzing the esterification of diacylglycerol with acyl-CoA.ResultsA dual-function PtWS/DGAT associated with diatom Phaeodactylum tricornutum is discovered in the current study. Distinctive to documented microalgal DGAT types, PtWS/DGAT exhibits activities of both a wax ester synthase (WS) and a DGAT. WS/DGATs are broadly distributed in microalgae, with different topology and phylogeny from those of DGAT1s, DGAT2s, and DGAT3s. In vitro and in vivo assays revealed that PtWS/DGAT, functioning as either a WS or a DGAT, exhibited a preference on saturated FA substrate. Endogenous overexpression of PtWS/DGAT demonstrated that the DGAT activity was dominant, whereas the WS activity was condition dependent and relatively minor. Compared with the wild type (WT), overexpression of PtWS/DGAT in the diatom resulted in increased levels of total lipids (TL) and triacylglycerol (TAG) regardless of nitrogen availability. The stability and scalability of the introduced traits were further investigated at a 10-L photobioreactor, where the mutant growth resembled WT, with moderately increased productivity of TL and TAG. Furthermore, the production of wax esters increased considerably (from undetectable levels to 2.83%) under nitrogen-deplete conditions.ConclusionsPtWS/DGAT is a bifunctional enzyme and may serve as a promising target for the engineering of microalga-based oils and waxes for future industrial use.Electronic supplementary materialThe online version of this article (10.1186/s13068-018-1029-8) contains supplementary material, which is available to authorized users.

Diatoms are important contributors to the benthic microeukaryote flora. This manuscript lays the foundation for future metagenomic and environmental sequencing projects off coastal China by curating diatom DNA sequences from the Yantai region of the Bohai and Yellow Seas ( Northeast China) . These studies are based on cultures established from samples collected in different seasons from marine littoral and supralittoral zones in 2013 and 2014. Thirty-six diatom strains were cultured successfully and identification of these clones was determined by light and scanning electron microscopy( LM and SEM) and DNA sequencing of the nuclear-encoded small subunit ribosomal RNA ( SSU) and chloroplast-encoded rbcL and psbC genes. The strains primarily represent raphid pennate genera, such as Amphora, Amphora ( Oxyamphora) , Caloneis, Diploneis, Halamphora, Navicula, Nitzschia, Parlibellus, Pleurosigma, Surirella and Tryblionella. When the DNA markers from these strains were analysed in a multi-gene phylogeny, we found that some clones-particularly within the genera Amphora, Navicula and Nitzschia-show greater than expected genetic diversity despite their very similar morphology and morphometrics. We also compared the molecular and morphological identities of several seemingly ubiquitous marine littoral taxa in the genera Amphora and Nitzschia from the Indian Ocean and Atlantic Ocean, the Red Sea and Adriatic Sea to their Yellow Sea counterparts.

Carotenoid cleavage dioxygenases (CCDs) are a group of enzymes that catalyze the oxidative cleavage steps from carotenoids to various carotenoid cleavage products. Someccdgenes have been identified and encoded enzymes functionally characterized in many higher plants, but little in cyanobacteria. We performed a comparative analysis ofccdsequences and explored their distribution, classification, phylogeny, evolution, and structure among 37 cyanobacteria. Totally 61 putativeccdsequences were identified, which are abundant inAcaryochloris marinaMBIC 11017, filamentous N2-fixing cyanobacteria, and unicellular cyanobacterialCyanothece. According to phylogenetic trees of 16SrDNAand CCD,ncedandccd8 genes occur later than the divergence ofccd7,apco, andccd1. All CCD enzymes share conserved basic structure domains constituted by a single loop formed with seven β-strands and one helix. In this paper, a general framework of sequence-function-evolution connection for theccdhas been revealed, which may provide new insight for functional investigation.

Carotenoids play crucial roles in structure and function of the photosynthetic apparatus of bacteria, algae, and higher plants. The formation of carotenoids from lycopene is catalyzed by the enzyme lycopene cyclase (LCY), which is structurally and functionally conserved in all organisms. A comparative genomic analysis regarding the LCY revealed that the higher plant (Arabidopsis thaliana) and the green alga (Ostreococcus sp. RCC809, Ostreococcus tauri, Ostreococcus lucimarinus, Micromonas sp. RCC299, Micromonas pusiua, Chlorella vulgaris, Volvox carteri, and Coccomyxa sp. C-169) possess two different LCY (beta-and epsilon-type). This indicated that an ancient gene duplication event must have occurred, which produced two classes of LCY in algae. However, some other green alga retained only one class of LCY, such as Haematococcus pluvialis (beta), Dunaliella salina (beta), Chlamydomonas reinhardtii (epsilon), and Chlorella sp. NC64A (epsilon), and the other gene copy was lost in these species. Furthermore, the similar LCY lost occurred in red alga (Cyanidioschyzon merolae) and Heterokontophyta (Phaeodactylum tricornutum and Thalassiosira pseudonana), which possess only the LCYB. In addition, the protein sequence of LCYB is highly similar to capsanthin-capsorubin synthase (CCS), which is another carotenogenic enzyme of plants. As a result, it is proposed that the CCS evolved from a duplicated LCYB. The discovery of two classes of LCY families in some algae suggests that carotenoid biosynthesis is differentially regulated in response to development and environmental stress in these algae, like members of LCY families are differentially regulated during development or stress in some higher plants.

The South China Sea is one of the largest marginal seas, with relatively frequent passage of eddies and featuring distinct spatial variation in the western tropical Pacific Ocean. Here, we report a phylogenetic study of bacterial community structures in surface seawater of the northern South China Sea (nSCS). Samples collected from 31 sites across large environmental gradients were used to construct clone libraries and yielded 2,443 sequences grouped into 170 OTUs. Phylogenetic analysis revealed 23 bacterial classes with major components α-, β- and γ-Proteobacteria, as well as Cyanobacteria. At class and genus taxon levels, community structure of coastal waters was distinctively different from that of deep-sea waters and displayed a higher diversity index. Redundancy analyses revealed that bacterial community structures displayed a significant correlation with the water depth of individual sampling sites. Members of α-Proteobacteria were the principal component contributing to the differences of the clone libraries. Furthermore, the bacterial communities exhibited heterogeneity within zones of upwelling and anticyclonic eddies. Our results suggested that surface bacterial communities in nSCS had two-level patterns of spatial distribution structured by ecological types (coastal VS. oceanic zones) and mesoscale physical processes, and also provided evidence for bacterial phylogenetic phyla shaped by ecological preferences.

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BackgroundCyanobacteria are photoautotrophic prokaryotes with wide variations in genome sizes and ecological habitats. Peroxiredoxin (PRX) is an important protein that plays essential roles in protecting own cells against reactive oxygen species (ROS). PRXs have been identified from mammals, fungi and higher plants. However, knowledge on cyanobacterial PRXs still remains obscure. With the availability of 37 sequenced cyanobacterial genomes, we performed a comprehensive comparative analysis of PRXs and explored their diversity, distribution, domain structure and evolution.ResultsOverall 244 putative prx genes were identified, which were abundant in filamentous diazotrophic cyanobacteria, Acaryochloris marina MBIC 11017, and unicellular cyanobacteria inhabiting freshwater and hot-springs, while poor in all Prochlorococcus and marine Synechococcus strains. Among these putative genes, 25 open reading frames (ORFs) encoding hypothetical proteins were identified as prx gene family members and the others were already annotated as prx genes. All 244 putative PRXs were classified into five major subfamilies (1-Cys, 2-Cys, BCP, PRX5_like, and PRX-like) according to their domain structures. The catalytic motifs of the cyanobacterial PRXs were similar to those of eukaryotic PRXs and highly conserved in all but the PRX-like subfamily. Classical motif (CXXC) of thioredoxin was detected in protein sequences from the PRX-like subfamily. Phylogenetic tree constructed of catalytic domains coincided well with the domain structures of PRXs and the phylogenies based on 16s rRNA.ConclusionsThe distribution of genes encoding PRXs in different unicellular and filamentous cyanobacteria especially those sub-families like PRX-like or 1-Cys PRX correlate with the genome size, eco-physiology, and physiological properties of the organisms. Cyanobacterial and eukaryotic PRXs share similar conserved motifs, indicating that cyanobacteria adopt similar catalytic mechanisms as eukaryotes. All cyanobacterial PRX proteins share highly similar structures, implying that these genes may originate from a common ancestor. In this study, a general framework of the sequence-structure-function connections of the PRXs was revealed, which may facilitate functional investigations of PRXs in various organisms.

The purpose of this study was to express an antimicrobial peptide in the chloroplast to further develop the plastid engineering of H. pluvialis. Homologous targeting of the 16S-trnI/trnA-23S region and four endogenous regulatory elements, including the psbA promoter, rbcL promoter, rbcL terminator, and psbA terminator in H. pluvialis, were performed to construct a chloroplast transformation vector for H. pluvialis. The expression of codon-optimized antimicrobial peptide piscidin-4 gene (ant1) and selection marker gene (bar, biolaphos resistance gene) in the chloroplast of H. pluvialis was controlled by the rbcL promoter and psbA promoter, respectively. Upon biolistic transformation and selection with phosphinothricin, integration and expression of ant1 in the chloroplast genome were detected using polymerase chain reaction (PCR), southern blotting, and western blotting. Using this method, we successfully expressed antimicrobial peptide piscidin-4 in H. pluvialis. Hence, our results showed H. pluvialis promises as a platform for expressing recombinant proteins for biotechnological applications, which will further contribute to promoting genetic engineering improvement of this strain.