Yahui Gao

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.

Sulfitobacter pseudonitzschiae sp. nov., isolated from the toxic marine diatom Pseudo-nitzschia multiseries.

A taxonomic study was carried out on bacterial strain H3(T), which was isolated from the toxic marine diatom Pseudo-nitzschia multiseries. Cells of strain H3(T) were Gram-stain-negative, rod-shaped, non-motile and capable of reducing nitrate to nitrite, but not denitrification. Growth was observed at NaCl concentrations of 1-9%, pH 6-12 and 10-37 °C. It was unable to degrade aesculin or gelatin. The dominant fatty acids (>10 %) were C18:1ω7c/ω6c (summed feature 8) and C16:0. The respiratory ubiquinone was Q10. The major lipids were phosphatidylethanolamine, phosphatidylglycerol, an aminolipid and one unknown lipid, and the minor lipids were two phospholipids and three unknown lipids. The G+C content of the chromosomal DNA was 61.7 mol%. 16S rRNA gene sequence comparison showed that strain H3(T) was related most closely to Sulfitobacter donghicola DSW-25(T) (97.3% similarity) and levels of similarity with other species of the genus Sulfitobacter were 95.1-96.9%. The mean (± sd) DNA-DNA hybridization value between strain H3(T) and Sulfitobacter donghicola DSW-25(T) was 18.0 ± 2.25%. The average nucleotide identity between strain H3(T) and Sulfitobacter donghicola DSW-25(T) was 70.45%. Phylogenetic analyses based on 16S rRNA gene sequences showed that strain H3(T) formed a separate clade close to the genus Sulfitobacter and was distinguishable from phylogenetically related species by differences in several phenotypic properties. On the basis of the phenotypic and phylogenetic data, strain H3(T) represents a novel species of the genus Sulfitobacter, for which the name Sulfitobacter pseudonitzschiae is proposed (type strain H3(T) =DSM 26824(T) =MCCC 1A00686(T)).

Cellular responses associated with ROS production and cell fate decision in early stress response to iron limitation in the diatom Thalassiosira pseudonana.

Investigation of how diatoms cope with the rapid fluctuations in iron bioavailability in marine environments may facilitate a better understanding of the mechanisms underlying their ecological success, in particular their ability to proliferate rapidly during favorable conditions. In this study, using in vivo biochemical markers and whole-cell iTRAQ-based proteomics analysis, we explored the cellular responses associated with reactive oxygen species (ROS) production and cell fate decision during the early response to Fe limitation in the centric diatom Thalassiosira pseudonana. Fe limitation caused a significant decrease in Photosystem (PS) II photosynthetic efficiency, damage to the photosynthetic electron transport chain in PS I, and blockage of the respiratory chain in complexes III and IV, which could all result in excess ROS accumulation. The increase in ROS likely triggered programmed cell death (PCD) in some of the Fe-limited cells through synthesis of a series of proteins involved in the delicate balance between pro-survival and pro-PCD factors. The results provide molecular-level insights into the major strategies that may be employed by T. pseudonana in response to Fe-limitation: the reduction of cell population density through PCD to reduce competition for available Fe, the reallocation of intracellular nitrogen and Fe to ensure survival, and an increase in expression of antioxidant and anti-PCD proteins to cope with stress.

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.

Diatom assemblages in surface sediments from the South China Sea as environmental indicators

We studied diatom distribution from 62 samples from the uppermost 1 cm of sediment in the South China Sea (SCS), using grabs or box corers in three cruises between 2001–2007. Fifty six genera, 256 species and their varieties were identified. Dominating species included Coscinodiscus africanus, Coscinodiscus nodulifer, Cyclotella stylorum, Hemidiscus cuneiformis, Melosira sulcata, Nitzschia marina, Roperia tesselata, Thalassionema nitzschioides, Thalassiosira excentrica, and Thalassiothrix longissima. Most surface sediments in the SCS were rich in diatoms, except for a few coarse samples. Average diatom abundance in the study area was 104 607 valve/g. In terms of the abundance, ecology, and spatial distribution, seven diatom zones (Zones 1–7) were recognized. Zone 1 (northern continental shelf) is affected by warm currents, SCS northern branch of the Kuroshio, and northern coastal currents; Zone 2 (northwestern continental shelf) is affected by intense coastal currents; Zone 3 (Xisha Islands sea area) is a bathyal environment with transitional water masses; Zone 4 (sea basin) is a bathyal-to-deep sea with stable and uniform central water masses in a semi-enclosed marginal sea; Zone 5 (Nansha Islands marine area) is a pelagic environment with relatively high surface temperature; Zone 6 (northern Sunda Shelf) is a tropical shelf environment; and Zone 7 (northern Kalimantan Island shelf area) is affected by warm waters from the Indian Ocean and coastal waters. The data indicate that these diatom zones are closely related to topography, hydrodynamics, temperature, nutrients and especially the salinity. Better understanding of the relationship between diatom distribution and the oceanographic factors would help in the reconstruction of the SCS in the past.

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.