Jeng Chang

Identification of a High-Affinity Phosphate Transporter Gene in a Prasinophyte Alga, Tetraselmis chui, and Its Expression under Nutrient Limitation

ABSTRACT A high-affinity phosphate transporter gene, TcPHO, was isolated from a growth-dependent subtracted cDNA library of the marine unicellular alga Tetraselmis chui. The full-length cDNA of TcPHO obtained by 5′ and 3′ rapid amplification of cDNA ends was 1,993 bp long and encoded an open reading frame consisting of 610 amino acids. The deduced amino acid sequence of TcPHO exhibited 51.6 and 49.8% similarity to the amino acid sequences of PHO89 from Saccharomyces cerevisiae and PHO4 from Neurospora crassa, respectively. In addition, hydrophobicity and secondary structure analyses revealed 12 conserved transmembrane domains that were the same as those found in PHO89 and PHO4. The expression of TcPHO mRNA was dependent on phosphate availability. With a low-phosphate treatment, the TcPHO mRNA concentration increased sharply to 2.72 fmol μg of total RNA−1 from day 1 to day 2 and remained at this high level from days 2 to 4. Furthermore, rescue treatment with either phosphate or p-nitrophenyl phosphate effectively inhibited TcPHO mRNA expression. In contrast, TcPHO mRNA expression stayed at a low level (range, 0.25 to 0.28 fmol μg of total RNA−1) under low-nitrate conditions. The expression pattern suggests that TcPHO can be used as a molecular probe for monitoring phosphorus stress in T. chui.

Effect of the Kuroshio intrusion on the chlorophyll distribution in the southern East China Sea during spring 1993

Abstract In order to assess the effect of the Kuroshio intrusion on phytoplankton biomass in the southern East China Sea north of Taiwan, chlorophyll a distributions observed before and after the recession of the seasonal Kuroshio intrusion were compared. Weekly hydrographie surveys and moored current meter data showed that the Kuroshio intruded onto the shelf under the prevailing northeasterly in early April 1993, and it retreated in early May 1993 shortly after the cessation of the northeasterly. The chlorophyll a distribution showed an eminent increase with a concentric distribution pattern, which was obviously related to the re-emergence of the year-round upwelling at the shelf break northeast of Taiwan. Strengthened upwelling was evidenced by a concomitant increase of nitrate concentration in the subsurface water near the shelf break. The mean value of the euphotic zone integrated chlorophyll a concentration in the normal upwelling area increased from 16 to 36 mg m−2 after the Kuroshio withdrawal. The high chlorophyll a concentration in the upwelling region was shown associated with the high primary productivity measured in the following year, May 1994. The euphotic zone integrated chlorophyll a concentration and primary production in the upwelling water were found to be 33 mg m−2 and 1540 mgC m−2 d−1, respectively. The higher chlorophyll and primary production was apparently the results of ample nutrient supply from the upwelling. At the same time, very high primary production was found in the mainland China coastal water with a value of 1900 mgC m−2 d−1 corresponding to a dinofiagellate bloom with population densities exceeding 1 × 104 cells 1t-1. The Kuroshio water, on the other hand, has the lowest primary production value of 420 mgC m−2 d−1.

Cooccurrence of ScDSP Gene Expression, Cell Death, and DNA Fragmentation in a Marine Diatom, Skeletonema costatum

ABSTRACT A novel death-specific gene, ScDSP, was obtained from a death stage subtraction cDNA library of the diatom Skeletonema costatum. The full length of ScDSP cDNA was 921 bp in length, containing a 699-bp open reading frame encoding 232 amino acids and two stretches of 66 and 156 bp in the 5′ and 3′ untranslated regions, respectively. Analysis of the peptide structure revealed that ScDSP contained a signal peptide domain, a transmembrane domain, and a pair of EF-hand motifs. When S. costatum grew exponentially at a rate of 1.3 day−1, the ScDSP mRNA level was at 2 μmol · mole 18S rRNA−1. In contrast, when the culture entered the death phase with a growth rate decreasing to 0.5 day−1, ScDSP mRNA increased dramatically to 668 μmol · mole 18S rRNA−1, and a high degree of DNA fragmentation was simultaneously observed. Under the influence of a light-dark cycle, ScDSP expression in both exponential and stationary phases clearly showed a diel rhythm, but the daily mean mRNA level was significantly higher in the stationary phase. Our results suggest that ScDSP may play a role in the molecular mechanism of self-destructive autolysis in phytoplankton under stress.

Nitric oxide as a signaling factor to upregulate the death-specific protein in a marine diatom, Skeletonema costatum, during blockage of electron flow in photosynthesis.

ABSTRACT To determine the physiological functions of a novel death-specific protein gene, Skeletonema costatum DSP-1 (ScDSP-1) in a marine diatom, Skeletonema costatum, the mRNA abundance of ScDSP-1 was measured in cultures subjected to light manipulation and treatments with various chemicals. When cells were transferred to a dim light intensity of 15 μmol m−2 s−1, ScDSP-1 mRNA levels showed a transient increase of 1 to 17.2 μmol (mol 18S rRNA)−1 in 60 h. Furthermore, treatments with the photoinhibitors 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) and 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone (DBMIB) resulted in high ScDSP-1 mRNA levels, which reached 943 and 72 μmol (mol 18S rRNA)−1, respectively. Treatment with the nitric oxide (NO) donor diethylamine nitric oxide also induced ScDSP-1 expression, and this inducible expression was inhibited by the NO scavenger hemoglobin. Additionally, the expression of ScDSP-1 mRNA elicited by DCMU and DBMIB was efficiently reduced when cultures were pretreated with the cell-penetrating NO scavenger 2-(4-carboxyphenyl)-4,5-dihydro-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide. In contrast, treatment with another photoinhibitor, paraquat, had no effect on ScDSP-1 expression. Our results indicated that NO is the crucial secondary messenger which signals the expression of ScDSP-1 when electron flow between photosystem II and photosystem I is blocked in S. costatum cells. In addition, the discovery of a similar gene, ScDSP-2, is briefly described.

The coupling of oligotrich ciliate populations and hydrography in the East China Sea: spatial and temporal variations

Abstract Variations in the spatial and temporal distribution of oligotrich ciliate populations in the East China Sea were investigated during four cruises of the R/V Ocean Researcher I between December 1997 and October 1998. Over the entire continental shelf, a seasonal cycle was found with a distinct 3–5-fold increase in the abundance of oligotrich ciliates in summer. This increase appeared to be induced by the tremendous summertime runoff from the Changjiang. A radial-type spatial distribution pattern also was observed in summer, with population densities higher toward the Changjiang plume but highest of all in the margins of the plume. In spring and fall, the spatial distribution of the oligotrich ciliates was closely correlated to the abundance of cyanobacterium Synechococcus. In summer in the plume region, mixotrophic ciliates accounted for over 50% of the total ciliate population, compared to less than 30% outside the plume or that in other seasons. We propose a model in which these ciliates constitute part of the pathway through which the particulate and dissolved organic carbon in the runoff water is incorporated into the oceanic food web.

Winter Distribution of Diatom Assemblages in the East China Sea

We examined the spatial distributional relationships between diatom assemblages and water types during the winter in the East China Sea. Principal component analysis was used to identify two water types and two diatom assemblages in the study area. Coastal water types along the mainland China coastline had low temperature and salinity levels, but high nitrate levels. The shelf-mixing water type in the rest of the study area had higher temperatures and salinities and lower levels of nitrate. Diatom assemblage distribution was not spatially consistent with water type. The Kuroshio assemblage had a large standing stock, distributed along the surface of the shelf break. This assemblage is likely the result of Kuroshio surface water coming into contact with nutrient-rich water in the shelf area, triggering proliferation of certain diatom species. A background assemblage with low standing stock level persisted over the entire study area in both coastal water and the shelf-mixing water types. Our results support previous research: the background assemblage is due to poor growth conditions such as the convection of water during winter; there were no significant seasonal variations in the species composition.

Effects of Asian Dust Storms on Synechococcus Populations in the Subtropical Kuroshio Current

Asian dust storms (ADSs) are the major source of dust deposition in the Northwest Pacific Ocean. To gain a better understanding on how ADSs affect the ecology of picophytoplankton in this oligotrophic region, five oceanographic cruises were conducted between March 15 and April 15, 2006 on a segment of the Kuroshio Current near the shelf break of the East China Sea (25.05° N, 123.15° E). During the study period, three ADS events were recorded and increases in nutrient concentrations as well as mixing depths were observed. Most of the ADS events stimulated the growth of Synechococcus, but the abundance of Prochlorococcus either remained unaffected or showed mild declines. A more detailed study was conducted during the ADS event between March 16 and 19. Phylogenetic analysis of 16S ribosomal RNA nucleotide sequences revealed that most of the newly appeared Synechococcus belonged to the clade II lineage. Furthermore, messenger RNA (mRNA) levels of three nutrient deficiency indicators, including idiA (an iron deficiency indicator), ntcA (a nitrogen deficiency indicator), and pstS (a phosphorus deficiency indicator), were analyzed by real-time quantitative reverse-transcription polymerase chain reaction. As this ADS event proceeded, mRNA levels of all these indicators decreased from relatively high to non-detectable values. These results suggest that the contributions of iron, nitrogen, and phosphate by the dust deposition from ADSs promote the growth of Synechococcus in the Kuroshio Current.

Reply to comment by Jinchun Yuan et al. on “Reduction of primary production and changing of nutrient ratio in the East China Sea: Effect of the Three Gorges Dam?”

[1] A brief discussion is presented here in response to Yuan et al.’s [2007] comment on our paper entitled ‘‘Reduction of primary production and changing of nutrient ratio in the East China Sea: Effect of the Three-Gorges Dam?’’ [Gong et al., 2006]. [2] First, we would like to point out that our research provides sufficient seasonal variations using accurate chlorophyll a (Chl a) data in the traditionally nutrient-rich (TNR) region of the East China Sea, as determined in several previous high-frequency sea-based investigations [Gong et al., 1996, 2003, 2006]. In contrast, Yuan et al. [2007] used questionable Chl a data (derived from the SeaWiFS OC4 algorithm: see second point) to study the inter-annual variations in Chl a in the entire East China Sea. This is clearly apparent in Figure 1 which illustrates the comparison between our average sea-based Chl a concentrations in the entire East China Sea (solid brown stars in Figure 1) and the SeaWiFS-derived Chl a data reported in Figure 2 of Yuan et al.’s comment. The results show that the SeaWiFS-derived Chl a data were substantially higher than our sea-based Chl a data. There can be no question that Yuan et al.’s [2007] data were invalid. [3] Second, we further question the accuracy of the SeaWiFS-derived Chl a data for the East China Sea which were used in Yuan et al.’s [2007] comments. Our reasons are as follows: [4] (1) It is widely believed that the standard SeaWiFSOC4 chlorophyll algorithm is only valid for ‘‘Case 1 waters’’ [O’Reilly et al., 1998; Carder et al., 1999]. But this type of global algorithm is flawed when it comes to ‘‘Case 2 waters’’ [Mueller and Austin, 1995; International Ocean-Colour Coordinating Group, 2000; Liew et al., 2001; Gong, 2004]. The key reason for the algorithmic failure in the case of ‘‘Case 2 waters’’ is that there is interference from the strong absorption of colored dissolved organic matter (CDOM) in the blue band that overlaps with phytoplankton chlorophyll absorption. When the absorption coefficient due to colored dissolved organic matter at 380 nm (acdom(l = 380 nm)) is greater than 0.1 m 1 [Mueller and Austin, 1995], the ocean waters are regarded as ‘‘Case 2 waters’’, and the use of the global satellite ocean-color OC4 algorithm is inappropriate. But unfortunately, Yuan et al. [2007] used the OC4 algorithm to process their Chl a data for the East China Sea, a region with ‘‘Case 2 waters.’’ [5] (2) O’Reilly et al. [1998] collected a large data set including coincident in-situ chlorophyll and remote sensing information to evaluate the performance of a wide variety of ocean color chlorophyll algorithms for SeaWiFS data. One of their conclusions is that, while the performance of the OC4 was superior to that of the OC2, it is not as suitable as the initial operational algorithm for SeaWiFS-derived Chl a data because its use requires accurate atmospheric correction and on-orbit calibrations in four bands (instead of two). They explain that this can only be assessed after the collection of sufficient data to validate and fine-tune sensor calibrations. It is currently widely known that atmospheric pollution in the shelf area of the East China Sea is very serious because of rapid industrial development in the coastal cities of China. Additionally, the high frequency of Asian dust storms has been observed in the East China Sea. As a result, the SeaWiFS-derived Chl a data are not likely very accurate without proper atmospheric correction. A second conclusion by O’Reilly et al. [1998] is that ‘‘Case 2 waters’’ present additional complications and challenges as their properties change depending on whether they are dominated by CDOM, nochlorophyllous particles, or a variable mix of both [Carder et al., 1989]. In short, specific algorithms or different parameterizations are required to process data from different regions. [6] (3) Gong [2004] presented CDOM data for four seasons from surface waters of the entire East China Sea. These data showed that the values of acdom(l = 325 nm) were higher than 0.2 m 1 (equivalent to acdom(l = 380 nm) = 0.1 m ) for most of the shelf waters year-round (Figure S1 of the auxiliary material). Figure S1 clearly shows that the values of acdom(l = 380 nm) in the TNR region are always higher than 0.1 m . These results support the optical classification of the TNR region as ‘‘Case 2 waters.’’ Additionally, a significant overestimation of the SeaWiFS-derived Chl a concentrations (2.3 mg m ) at a station located about 200 km east off the Changjiang River mouth (see star-symbol in Figure S1a) was found in

Strains of the Morphospecies Ploeotia costata (Euglenozoa) Isolated from the Western North Pacific (Taiwan) Reveal Substantial Genetic Differences

Two phagotrophic euglenid strains (Strains Pac and Tam) were isolated from coastal locations in Taiwan. Ultrastructural characteristics of the strains included five pellicle strips joined at the posterior end. The strips were formed by major grooves with bifurcated edges. At the cell anterior, the feeding structure formed a lip. Underneath the lip was a comb composed of layers of microtubules. Farther back, two supporting rods tapered toward the posterior end, and a number of vanes with attached microtubules were present between the rods. The morphological characteristics agree with Ploeotia costata Strain CCAP 1265/1. However, the 18S rDNA sequences of Strains Pac/Tam lacked a group I intron and possessed three extra insertions of 116, 67, and 53 bp. Phylogenetic analysis indicated low sequence similarity between Strains Pac/Tam and CCAP 1265/1 (92%). The morphospecies P. costata apparently includes a substantial level of DNA sequence divergence, and likely represents multiple molecular species units.

Identification of Microalgae by Laser Desorption/Ionization Mass Spectrometry Coupled with Multiple Nanomatrices

AbstractIn this study, we demonstrate a simple method to identify microalgae by surface-assisted laser desorption/ionization mass spectrometry (SALDI-MS) using three different substrates: HgSe, HgTe, and HgTeSe nanostructures. The fragmentation/ionization processes of complex molecules in algae varied according to the heat absorption and transfer efficiency of the nanostructured matrices (NMs). Therefore, the mass spectra obtained for microalgae showed different patterns of m/z values for different NMs. The spectra contained both significant and nonsignificant peaks. Constructing a Venn diagram with the significant peaks obtained for algae when using HgSe, HgTe, and HgTeSe NMs in m/z ratio range 100–1000, a unique relationship among the three sets of values was obtained. This unique relationship of sets is different for each species of microalgae. Therefore, by observing the particular relationship of sets, we successfully identified different algae such as Isochrysis galbana, Emiliania huxleyi, Thalassiosira weissflogii, Nannochloris sp., Skeletonema cf. costatum, and Tetraselmis chui. This simple and cost-effective SALDI-MS analysis method coupled with multi-nanomaterials as substrates may be extended to identify other microalgae and microorganisms in real samples. Graphical AbstractIdentification of microalgae by surface-assisted laser desorption/ionization mass spectrometry coupled with three different mercury-based nanosubstrates