Changping Chen

Biomass, total lipid production, and fatty acid composition of the marine diatom Chaetoceros muelleri in response to different CO2 levels

The marine diatom Chaetoceros muelleri grown under air (0.03% CO2), 10%, 20%, and 30% CO2 conditions was evaluated to determine its potential for CO2 reduction coupled with biodiesel production. The results indicated that C. muelleri grows well with high CO2 aeration levels (10-20%) and is induced to accumulate lipids under 10-30% CO2. In particular, the highest values of the maximum biomass concentration (1.059gL(-1)), maximum specific growth rate (0.868d(-1)), maximum biomass productivity (0.272gL(-1)d(-1)), maximum CO2 biofixation (0.428gL(-1)d(-1)), and total lipid (43.40% dry weight) and neutral lipid contents were all obtained with 10% CO2 aeration. Moreover, the analysis of the fatty acid composition of C. muelleri revealed the predominance of C14-C18 fatty acids (>90%) and saturated and monounsaturated fatty acids (>80%) under all CO2 levels. The results suggest that C. muelleri has great potential to biodiesel production using flue gases.

iTRAQ-Based Proteomic Analysis of the Metabolism Mechanism Associated with Silicon Response in the Marine Diatom Thalassiosira pseudonana

Silicon is a critical element for diatom growth; however our understanding of the molecular mechanisms involved in intracellular silicon responses are limited. In this study, an iTRAQ-LC-MS/MS quantitative proteomic approach was coupled with an established synchrony technique to reveal the global metabolic silicon-response in the model diatom Thalassiosira pseudonana subject to silicon starvation and readdition. Four samples, which corresponded to the time of silicon starvation, girdle band synthesis, valve formation, and right after daughter cell separation (0, 1, 5, 7 h), were collected for the proteomic analysis. The results indicated that a total of 1,831 proteins, representing 16% of the predicted proteins encoded by the T. pseudonana genome, could be identified. Of the identified proteins, 165 were defined as being differentially expressed proteins, and these proteins could be linked to multiple biochemical pathways. In particular, a number of proteins related to silicon transport, cell wall synthesis, and cell-cycle progress could be identified. In addition, other proteins that are potentially involved in amino acid synthesis, protein metabolism, and energy generation may have roles in the cellular response to silicon. Our findings provide a range of valuable information that will be of use for further studies of this important physiological response that is unique to diatoms.

Morphology, phylogeny and ITS-2 secondary structure of Pseudo-nitzschia brasiliana (Bacillariophyceae), including Chinese strains

Wang P., Liang J., Lin X., Chen C., Huang Y., Gao Y. and Gao Y. 2012. Morphology, phylogeny and ITS-2 secondary structure of Pseudo-nitzschia brasiliana (Bacillariophyceae), including Chinese strains. Phycologia 51: 1–10. DOI: 10.2216/09-108.1 The diatom Pseudo-nitzschia brasiliana Lundholm, Hasle & G.A. Fryxell is documented from China for the first time. Strains isolated from southeast coastal waters were characterized using light and electron microscopic observation. All strains were tested for domoic acid, but no toxin was detected. Genetic diversity and phylogenetic relationships of global strains of P. brasiliana were studied to assess intraspecific variation and geographic distribution patterns. Phylogenetic analyses based on the large subunit rDNA gene together with morphological observations show that P. brasiliana from China and other locations worldwide form one well-supported monophyletic clade, with P. americana as its sister. Phylogenetic analyses of internal transcribed spacer (ITS) rDNA sequences show a clear separation between five Asian strains and three European strains. In addition, ITS-2 rDNA secondary structure analyses reveal genetic variation between P. brasiliana strains from Europe and Southeast Asia, namely, a transfer of a base-pair set from a loop in the Asian group to the basis of helix II in the European group and two hemi-compensatory base changes (hemi-CBCs) in helix III between one European strain (ICMB-176) and the other strains. The occurrence of P. brasiliana in Chinas coastal waters is discussed.

MALDI-TOF MS analysis of the extracellular polysaccharides released by the diatom Thalassiosira pseudonana under various nutrient conditions

Investigation of the production and structural characteristics of the extracellular polysaccharides (ECPS) released by diatoms according to nutrient status is urgently necessary for our understanding of the roles of ECPS in aquatic ecosystem. In this study, the effects of N and P depletion and variable nutrient sources on the production and structural characterization of the soluble ECPS released by the marine diatom Thalassiosira pseudonana in batch culture were examined. The abundance of the soluble ECPS produced under N (NO3−) depletion was higher than that obtained in the P (PO43−) depletion and control treatments. NH4+ rather than NO3− and urea and sodium-glycerophosphate rather than PO43− were found to induce a higher abundance of soluble ECPS production at the end of the experiment, indicating that the abundance of soluble ECPS is also affected by the nutrient source. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) analysis of the structural characteristics of the soluble ECPS samples showed that the degree of polymerization (d.p.) profiles and the distribution of the polymers with different molecular masses varied in response to nutrient depletion and different nutrient sources. An increase in the proportion of both low- and high-molecular-weight polymers under the N (NO3−) and P (PO43−) depletion treatments was found. Based on the different characteristics of high- and low-molecular-weight polymers, our results suggest that the production of soluble ECPS may be one of the strategies that T. pseudonana utilizes to survive under nutrient stress conditions.

Seasonal variations of phytoplankton assemblages and its relation to environmental variables in a scallop culture sea area of Bohai Bay, China

Seasonal variations of phytoplankton assemblages were examined in a scallop culture sea area of Bohai Bay (China) with regard to some major physical and chemical variables. Samples were collected at three stations from July 2011 to September 2013. A total of 134 species belong to 4 phyla were identified, of which 104 were diatoms, 27 were dinoflagellates, 1 was euglenophyte and 2 were chrysophytes. The cells abundance in autumn (55.44×103cells/L) was higher than that in summer (6.99×103cells/L), spring (3.46×103cells/L) and winter (2.69×103cells/L). The Shannon-Wiener diversity index was higher in summer (3.06), followed by spring (3.02) and winter (2.91), and low in autumn (1.40). Results of canonical correspondence analysis showed that phosphate, salinity, temperature, silicate and DIN/SiO2 ratio were the most important environmental factors influencing the variation of phytoplankton community structure. It is suggested that eutrophication resulted from scallop culture would cause a potential red tide risk.

Influences of sea ice on eastern Bering Sea phytoplankton

The influence of sea ice on the species composition and cell density of phytoplankton was investigated in the eastern Bering Sea in spring 2008. Diatoms, particularly pennate diatoms, dominated the phytoplankton community. The dominant species were Grammonema islandica (Grunow in Van Heurck) Hasle, Fragilariopsis cylindrus (Grunow) Krieger, F. oceanica (Cleve) Hasle, Navicula vanhoeffenii Gran, Thalassiosira antarctica Comber, T. gravida Cleve, T. nordenskiöeldii Cleve, and T. rotula Meunier. Phytoplankton cell densities varied from 0.08×104 to 428.8×104 cells/L, with an average of 30.3×104 cells/L. Using cluster analysis, phytoplankton were grouped into three assemblages defined by ice-forming conditions: open water, ice edge, and sea ice assemblages. In spring, when the sea ice melts, the phytoplankton dispersed from the sea ice to the ice edge and even into open waters. Thus, these phytoplankton in the sea ice may serve as a “seed bank” for phytoplankton population succession in the subarctic ecosystem. Moreover, historical studies combined with these results suggest that the sizes of diatom species have become smaller, shifting from microplankton to nannoplankton-dominated communities.

Facile sand enhanced electro-flocculation for cost-efficient harvesting of Dunaliella salina

Energy consumption and water resource in the cultivation and harvesting steps still need to be minimized for the popularization of the microalgae-based products. An efficient electro-flocculation method for harvesting Dunaliella Salina integrated with local sand has been successfully applied. Sand was effective for speeding up the processes of flocculation and sedimentation of algal flocs and the electrolytic hydroxides was essential to bridge the sand and small flocs into large dense flocs. The maximal recovery effective improved from 95.13% in 6min to 98.09% in 4.5min and the optimal electrical energy consumption decreased 51.03% compared to conventional electro-flocculation in a laboratory ambient condition. Furthermore, reusing the flocculated medium in cultivation of the D. Salina with nitrogen supplemented performed no worse than using fresh medium. This sand enhanced electro-flocculation (SEF) technology provides a great potential for saving time and energy associated with improving microalgae harvesting.

Observations of several cryptomonad flagellates from China Sea by scanning electron microscopy

Three species and one variety of cryptomonad flagellates belonging to three genera were observed with the scanning electron microscope in sea water samples from Tolo Harbor (Hong Kong), Changjiang River Estuary and Xiamen Harbor. They are Hemiselmis sp. Novarino, Plagioselmis prolonga Butcher ex Novarino, Lucas & Morrall, Plagioselmis prolonga var. nordica Novarino, Lucas & Morrall and Teleaulax acuta (Butcher) Hill. The taxonomic characteristics, ecological habit and distribution of the above species are described and the LM and SEM photographs of the species are also presented. This is the first record of the genus Hemiselmis Parke in the China Sea, and the species Plagioselmis prolonga and Teleaulax acuta have records of producing blooms in the China Sea.

Variations in the Total Lipid Content and Biological Characteristics of Diatom Species for Potential Biodiesel Production

The selection of suitable and indigenous species is a fundamental requirement in developing oil-rich microalgae for biodiesel production. So it is necessary to evaluate the growth characteristics and lipid content of the interested microalgae species and obtain a basic knowledge about their potential towards biodiesel production. In this study, the total lipid content and biomass concentration under normal culture conditions of thirty- five diatom species (with twenty-six species being studied for the first time) belonging to nineteen genera obtained from different locations were examined. The results showed that the total lipid content is species-dependent, ranging from 4.86% to 48.61% dry weight. Twenty-four strains (64.9%) had total lipid contents higher than 20% dry weight, and nine strains (24.3%) had total lipid contents greater than 30% dry weight. Achnanthes amoena and Proschkinia sp. had total lipid contents up to 48.61% and 41.42% dry weight, respectively. Compared with the centric diatoms, most species with high lipid content were pennate. In addition, various biological characteristics were documented, including cell size and the ability to survive in various environments. The results revealed that some diatom species here such as Bacillaria paradoxa, Navicula molli, Navicula halophila and Phaeodactylum tricornutum could be regarded as potential sources for biodiesel production.

Cellular metabolic responses of the marine diatom Pseudo-nitzschia multiseries associated with cell wall formation

In this study a comparative proteomics approach involving a mass spectrometric analysis of synchronized cells was employed to investigate the cellular-level metabolic mechanisms associated with siliceous cell wall formation in the pennate diatom Pseudo-nitzschia multiseries. Cultures of P. multiseries were synchronized using the silicate limitation method. Approximately 75% of cells were arrested at the G2+M phase of the cell cycle after 48 h of silicate starvation. The majority of cells progressed to new valve synthesis within 5h of silicon replenishment. We compared the proteome of P. multiseries at 0, 4, 5, and 6h of synchronization progress upon silicon replenishment using two-dimensional gel electrophoresis. Forty-eight differentially expressed protein spots were identified in abundance (greater than two-fold change; P<0.005), some of which are predicted to be involved in intracellular trafficking, cytoskeleton, photosynthesis, lipid metabolism, and protein biosynthesis. Cytoskeleton proteins and clathrin coat components were also hypothesized to play potential roles in cell wall formation. The proteomic profile analysis suggests that P. multiseries most likely employs multiple synergistic biochemical mechanisms for cell wall formation. These results improve our understanding of the molecular mechanisms underlying silicon cell wall formation and enhance our understanding of the important role played by diatoms in silicon biogeochemical cycling.