Elucidating colony bloom formation mechanism of a harmful alga Phaeocystis globosa (Prymnesiophyceae) using metaproteomics.

Phaeocystis is a globally distributed Prymnesiophyte genus and usually forms massive harmful colony blooms, which impact marine ecosystem, mariculture, human health, and even threaten coastal nuclear power plant safety. However, the mechanisms behind the colony formation from the solitary cells remain poorly understood. Here, we investigated metabolic processes of both solitary and non-flagellated colonial cells of Phaeocystis globosa at different colony bloom stages in the subtropical Beibu Gulf using a metaproteomic approach. Temperature was significantly correlated with Phaeocystis colony bloom formation, and the flagellated motile solitary cells with abundant flagellum-associated proteins, such as tubulin and dynein, were the exclusive cellular morphotype at the solitary cell stage featured with temperatures ≥21 °C. When the temperature decreased to <21 °C, tiny colonies appeared and the flagellum-associated proteins were down-regulated in both solitary and non-flagellated colonial cells, while proteins involved in biosynthesis, chain polymerization and aggregation of glycosaminoglycan (GAG), a key constituent of gelatinous matrix, were up-regulated, indicating the central role of active GAG biosynthesis during the colony formation. Furthermore, light utilization, carbon fixation, nitrogen assimilation, and amino acid and protein synthesis were also enhanced to provide sufficient energy and substrates for GAG biosynthesis. This study highlighted that temperature induced re-allocation of energy and substances toward GAG biosynthesis is essential for colony bloom formation of P. globosa.

Comparative study of polycyclic aromatic hydrocarbons (PAHs) and heavy metals (HMs) in corals, sediments and seawater from coral reefs of Hainan, China.

This work investigated levels of PAHs and HMs in fourteen species from seven genera of scleractinian corals, adjacent sediments, and surface seawater in Hainan, China. The sources of contaminations were analyzed as well. The results showed that scleractinian corals had a relatively higher bioaccumulation capacity for PAHs from sediments than for HMs. There were inter-species differences for these contaminants enriched in corals. Pavona varians and Porites lutea could accumulate PAHs more readily. While higher concentrations of Cr, Mn and Pb occurred in Favites flexuosa, other metal levels, such as for Ni, Cu, Zn and As, were found to be elevated in Pocillopora damicornis, as well as for Cd in Acropora echinata. It was found that PAHs originated from petrogenic and pyrolytic sources, and were mainly linked to onshore and on-sea activities, such as motorboats. Mn, Ni, As and Cd were from crustal materials or natural weathering, while Cr, Cu, Zn and Pb were non-crustal origin connecting with the use of anti-fouling boat paint and agricultural and/or aquacultural chemicals. This study suggested that corals could serve as good bioindicators for two types of chemical pollution in the reef system, especially for the two species P. varians and P. lutea for PAHs contaminants.

Comparative transcriptomics reveals colony formation mechanism of a harmful algal bloom species Phaeocystis globosa.

Phaeocystis globosa is a major causative agent of harmful algal blooms in the global ocean, featuring a complex polymorphic life cycle alternating between free-living solitary cells and colonial cells. Colony is the dominant morphotype during P. globosa bloom. However, the underlying mechanism of colony formation is poorly understood. Here, we comprehensively compared global transcriptomes of P. globosa cells at four distinctive colony formation stages: free-living solitary cells, two cell-, four cell- and multi-cell colonies, under low (20 °C) and high (32 °C) temperatures, and characterized the genes involved in colony formation. Glycosaminoglycan (GAG) synthesis was enhanced while its degradation was decreased during colony formation, resulting in the accumulation of GAGs that are an essential substrate of the colony matrix. Nitrogen metabolism and glutamine synthesis were remarkably increased in the colonial cells, which provided precursors for GAG synthesis. Furthermore, cell defense and motility were down-regulated in the colonial cells, thereby conserving energy for GAG synthesis. Notably, high temperature led to decreased synthesis and increased degradation of GAGs, resulting in insufficient substrates to form the colony. Our study indicates that GAGs accumulation is critical for colony formation of P. globosa, but high temperature inhibits GAGs' accumulation and colony formation.

Comparative study of polycyclic aromatic hydrocarbons (PAHs) and heavy metals (HMs) in corals, surrounding sediments and surface water at the Dazhou Island, China.

This study investigated polycyclic aromatic hydrocarbons (PAHs) content in corals (Acropora sp.), surficial sediments, and surface seawater, and heavy metals (HMs) contents in corals and sediments from Dazhou Island, Hainan, China. Concentrations of PAHs in seawater and sediment seasonally ranged from 191.5 ng L-1 to 587.7 ng L-1, and from 37.9 ng g-1 to 233 ng g-1, while levels in corals were higher (185.2-545.0 ng g-1) compared to those found in sediments, demonstrating bioaccumulation of PAHs by corals. A similar seasonally variation of PAHs was observed in water/sediments and corals, and the proportions of low molecular weight PAHs (LPAHs) in seawater and corals were higher. Pyrolytic and petrogenic contaminations were identified to be the main sources of PAHs. Lower HMs concentrations were detected in corals (9.8-39.4 µg g-1) than in sediments (65.0-83.3 µg g-1), but HMs bioaccumulation still occurs in corals. Higher concentrations of HMs in sediment and corals were detected in March and December, especially Mn and Zn. Application of an enrichment factor showed that Cu in corals was delivered from non-crustal materials, and anthropogenic inputs were possibly the main sources. According to Biota Sediment Accumulation Factor, corals could strongly bioaccumulate LPAHs and Cd, and PAHs at a higher (p < 0.05) rate than HMs. There was a lack of correlation between the accumulation of PAHs and HMs in corals based on the cluster analysis. Dual hierarchical clustering analysis result revealed that feeding, instead of symbiosis, might be the main process responsible for the bioaccumulation of PAHs and HMs.

Transcriptional responses of Acropora hyacinthus embryo under the benzo(a)pyrene stress by deep sequencing.

Coral embryos are a critical and sensitive period for the early growth and development of coral. Benzo(a)pyrene (BaP) is widely distributed in the ocean and has strong toxicity, but there is little information on the toxic effects to coral embryos exposed to this widespread environmental contaminant. Thus, in this study, we utilized the Illumina Hiseq™ 4000 platform to explore the gene response of Acropora hyacinthus embryos under the BaP stress. A total of 130,042 Unigenes were obtained and analyzed, and approximately 37.67% of those matched with sequences from four different species. In total, 2606 Unigenes were up-regulated, and 3872 Unigenes were down-regulated. After Gene Ontology (GO) annotation, the results show that the "cellular process" and "metabolic process" were leading in the category of biological processes, which the "binding" and "catalytic activity" were the most abundant subcategories in molecular function. Based on the Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis, the most differentially expressed genes (DEGs) were enriched, as well as down-regulated in the pathways of oxidative phosphorylation, metabolism of xenobiotics, immune-related genes, apoptosis and human disease genes. At the same time, 388,197 of Single-nucleotide Polymorphisms (SNPs) and 6164 of Simple Sequence Repeats (SSRs) were obtained, which can be served as the richer and more valuable SSRs molecular markers in the future. The results of this study can help to better understand the toxicological mechanism of coral embryo exposed to BaP, and it is also essential for the protection and restoration of coral reef ecosystem in the future.

Comparative evaluation of five protocols for protein extraction from stony corals (Scleractinia) for proteomics.

Corals especially the reef-building species are very important to marine ecosystems. Proteomics has been used for researches on coral diseases, bleaching and responses to the environment change. A robust and versatile protein extraction protocol is required for coral proteomics. However, a comparative evaluation of different protein extraction protocols is still not available for proteomic analysis of stony corals. In the present study, five protocols were compared for protein extraction from stony corals. The five protocols were TRIzol, phenol-based extraction (PBE), trichloroacetic acid (TCA)-acetone, glass bead-assisted extraction (GBAE) and a commercially available kit. PBE, TRIzol and the commercial kit were more robust for extracting proteins from stony corals. The protein extraction efficiency and repeatability, two dimensional electrophoresis (2-DE) and matrix-assisted laser desorption/ionization time of flight mass spectrometry (MALDI TOF MS) were employed to evaluate the protocols. The results indicated that PBE protocol had the better protein extraction efficiency than the others. Protein extraction coverage varied among the procedures. Each protocol favored for certain proteins. Therefore, it is very important for coral proteomic analysis to select a suitable protein protocol upon the experimental design. In general, PBE protocol can be the first choice for extracting proteins from stony corals.

Comparative Studies on the Toxicokinetics of Benzo[a]pyrene in Pinctada martensii and Perna viridis.

Research on the kinetics of Benzo[a]pyrene (B[a]P) bioaccumulation in the clam Pinctada martensii and mussel Perna viridis showed that the initial rate of uptake was directly related to the PAH concentrations in the ambient environment. The uptake and depuration rate constants were different at the four B[a]P exposure levels, which indicated that the toxicokinetic rate constants mainly depended on the exposure levels of pollutants to the environment. In addition, the uptake rate constants of B[a]P were higher than the depuration rate constants in the entire experiment. The comparison demonstrated that mussels release B[a]P more rapidly than clams. The bioconcentration factors (BCFs) of B[a]P varied from 3335 to 12892 in the clam and 2373-6235 in the mussel. These findings on the bioaccumulation kinetics for petroleum hydrocarbons, in association with the critical body residue, will be valuable when choosing sensitive organisms to assess the potential ecotoxicological risk to the marine environment.

Polycyclic aromatic hydrocarbons in surface sediment from Yangpu Bay, China: Distribution, sources and risk assessment.

The study investigated the occurrence of polycyclic aromatic hydrocarbons (PAHs) in the surface sediment from eleven sites in Yangpu Bay, China in December 2013 (winter) and July 2014 (summer). The 16 US EPA priority PAHs were found in the range of 1583.2-5701.7 ng/g dry weights with an average of 3134.7 ± 1241.3 ng/g in winter and ranged from 2161.8 to 4527.2 ng/g with an average of 3016.6 ± 748.0 ng/g in summer, respectively. The concentrations of the PAHs tended to be relatively high in comparison with other areas from the literatures. The identification using molecular indices analysis indicated that the PAHs originated mainly from pyrogenic and petrogenic sources in most of the sites. According to principle component analysis-multiple linear regression (PCA/MLR) for their source apportionment, the main sources of PAHs were vehicle emissions, petroleum products and biomass combustion. The risk assessment using international sediments quality guidelines and sediments quality criteria indicated that several PAHs, such as Nap, Flu, Phe, Ace, Acy and BghiP in most of the sites would potentially affect organisms in Yangpu Bay.