Taxonomy and phylogeny of the section Chaetoceros(Chaetocerotaceae,Bacillariophyta),with description of two new species

Chaetoceros Ehrenberg is one of the most diverse genera of planktonic diatoms.The species in section Chaetoceros are characterized by cells and setae having numerous chloroplasts and being widely distributed.However,the delimitations of some species are problematic because of limited morphological information in the classical descriptions.Monoclonal strains of the section Chaetoceros were established,morphological features were studied using light and electron microscopy,and the hypervariable D 1-D 3 region of the nuclear ribosomal large subunit gene was sequenced to address phylogenetic relationships.Fifteen species belonging to the section Chaetoceros were recorded,including two new species,C.hainanensis sp.nov.and C.tridiscus sp.nov.Chaetoceros hainanensis was characterized by straight chains,narrowly lanceolate to hexagonal apertures,sibling setae diverging in nearly right angles,stipule-shaped spines on terminal setae and arrowhead-shaped spines on intercalary setae.C.tridiscus had short straight chains,narrowly lanceolate apertures,arrowhead-shaped spines and circular poroids arranged in a grid pattern on terminal and intercalary setae.The phylogenetic analyses revealed six groups formed by 19 species within the section Chaetoceros,which was found to be monophyletic.The subdivision of the section is still not well understood.The morphological characters within each group varied considerably and molecular information on more species are needed to enrich the phylogenetic profiling.

Effects of light quality on growth rates and pigments of Chaetoceros gracilis(Bacillariophyceae)

Light is an important parameter in algal culturing.In this work,the effects of different light qualities on growth of the marine diatom Chaetoceros gracilis are evaluated.The cells were cultured under light quantum flux density of 60μmol photons/(m2·s)with nine light qualities:LED red light(LR),LED blue light(LB),LED red plus LED blue light(LR+LB),LED white light(LW),fluorescent white light(FW),and combinations of LW and FW lights with increased proportions of red or blue light(FW+LR,FW+LB,LW+LR,and LW+LB).Blue light promoted the growth of C.gracilis largely.Three light qualities,FW+LR,LW+LR,and LR,resulted in the lowest growth rate.Both chlorophyll and carotenoids reached the highest level under LB and the lowest level under LR among monochromatic light sources;however,increasing of the proportion of blue or red light in the white light induced an increase of the chlorophyll and carotenoid concentrations.Light absorption ability of microalgae was critical for the growth of these organisms,as we observed a positive correlation between the extinction coefficient at different wavelengths and the specific growth rate.These findings are of importance to improve the culturing of this alga in bioreactors.

Inhibition of photosynthesis in the microalga Chaetoceros curvisetus(Bacillariophyta) by macroalga Gracilaria lemaneiformis(Rhodophyta)

We investigated the effects of dried macroalga Gracilaria lemaneiform （Rhodophyta） on photosynthesis of the bloom-forming microalga Chaetoceros curvisetus. C. curvisetus was cultured with different amounts of dried G. lemaneiformis under controlled laboratory conditions. We measured the photosynthetic oxygen evolution rate and established the chlorophyll a fluorescence transient （OJIP） curve coupled with its specific parameters. We observed concentration-dependent and time-dependent relationships between dried G. lemaneiformis and inhibition of photosynthesis in C. curvisetus. Co-culture with dried G. lemaneiformis also resulted in a decrease in the light-saturated maximum photosynthetic oxygen evolution rate （P^ax） in C. curvisetus, and a decrease in the OJIP curve along with its specific parameters; the maximum photochemical efficiency of PSII （FJFm）, the amount of active PSII reaction centers per excited cross section at t=0 and t=--tFM （RC/CS0 and RC/CSm, respectively）, the absorption flux per excited cross section at t=0 （ABS/ CS0）, and the efficiency with which a trapped exciton moves an electron into the electron transport chain （~u0）. The dark respiration rate （Rd） increased in C. curvisetus co-cultured with dried G. lemaneiformis. The JIP-test and the oxygen evolution results indicated that dried G. lemaneiJbrmis decreased the number of active reaction centers, blocked the electron transport chain, and damaged the oxygen-evolving complex of C. curvisetus. This result indicated that dried fragments of G. lemaneiformis could effectively inhibit photosynthesis of C. curvisetus, and thus, could serve as a functional product to control and mitigate C. curvisetus blooms.

The study on the effect of NO on the growth of Chaetoceros curvisetus

This article studied nitric oxide (NO) effect on the growth of Chaetoceros curvisetus in chemistry for the first time. Nitric oxide was added into the media with 4 different nutrient concentrations f/2, f/50, f/100, and f/200 when the alga was growing. The growth of C. curvisetus could be obviously promoted or inhibited during the cultivation process in NO enriched media of different concentrations. The growth curve in such media showed a sharp single peak that is the optimal NO concentration for the alga growth, which is consistent with the influence of NO on the growth of high plants. In addition, C. curvisetus can produce NO by itself during the growth. Therefore, using NO could effectively regulate the algae growth, which is important in real tide control and remediation.

Nutrient compositions of cultured Skeletonema costatum,Chaetoceros curvisetus,and Thalassiosira nordenskildii

We cultured different-sized fractions of dominant phytoplankton species, Skeletonema costatum, Chaetoceros curvisetus, and Thalassiosira nordenskioldii, collected in different sea areas in various seasons, and measured and compared their C, N, P, Si contents. The N content of these species is similar, while the C, P, and Si contents of S. costatum from eutrophic Changjiang （Yangtze River） estuary are higher than those from Jiaozhou Bay （JZB）, particularly the content of Si. The C, N, P, and Si contents of cultured phytoplankton in JZB increase with size fraction augmentation, and the percentages of C, N, and P follow the same trend, while the percentage of Si remain constant. Moreover, S. costatum from small-sized fraction assimilated Si more easily than C. curvisetus and T. nordenskirldii, which is explained by the dominance of S. costatum under the conditions of low SiO3-Si concentration in JZB. The C, N, P, and Si contents of cultured S. costatum collected during summer and winter are higher, which is consistent with the phytoplankton blooming seasons in JZB. The SiO3-Si concentration of seawater during spring restrain the growth of phytoplankton, supported by the fact that the N, P, and Si contents and their ratios in cells of cultured S. costatum are low in spring season.

Enhancement Effects of Three Rare Earth Elements on the Growth of Chaetoceros Mulleri

Enhancement effects of rare earth elements on the growth of Chaetoceros mulleri is studied in this paper. The results show that all of the light, middle and heavy rare earth elements have similar enhancement effect on the growth of Chaetoceros mulleri, with the beneficial concentrations of La, Gd and Yb being 7.28～87.40 μ mol/L, 6.36～57.23 μ mol/L and 5.78～17.34 μ mol/L. The optimum concentrations of La, Gd and Yb are 7.28 ～50.98 μ mol/L,31.80～44.52 μ m ol/L and 5.78～17.34 1μ mol/L, respectively. When the concentrations of La, Gd and Yb are 7.28～87.40 μ mol/L, 6.36～57.23 μ mol/L and 5.78～ 17,34 μ mol/L, the concentrations of chlorophyll have increased by 9.3～47.0%, 33.4～44.3%, and 36.5～40.3%, respectively as compared with the control group. The mechanism of enhancement of rare earth elements on the growth ot Chaetoceros mulleri is also discussed in this paper.

Effect of NaNO_3 Concentrations on the Growth and Fatty Acid Compositions of Nitzschia closterium and Chaetoceros gracilis*

Fatty acid compositions of two strains of marine diatoms Nitzschia closterium ( MACC B222 ) and Chaetoceros gracilis ( MACC B13 ) have been examined. The microalgae have been grown at different initial NaNO3 concentrations ( 75, 375, 750, 1 125, 1 500, 1 875 mg/L ) and harvested at the late exponential phase. The results by one factor analysis of variance show that the NaNO3 concentrations have no significant influence on the relative growth rate of two strains of marine diatoms; the influence of NaNO3 concentrations on the fatty acids differs from species to species. The major fatty acids of two --diatom strains are 14:0, 16:0, 16:1n7 and 20:5n3 ( EPA ) , B13 also has high percentage -of 20:4n6 ( 6.0 ~ 9.1% ).

EXTRACELLULAR DISSOLVED ORGANIC CARBON OF A MARINE NANOPLANKTONIC DIATOM CHAETOCEROS SP.:INFLUENCE OF DAILY RHYTHM,LIGHT AND TEMPERATURE

The extracellular dissolved organic, carbon (DOC) and algal cell particlutate organiccarbon (POC) of a marine nanoplanktonic diatom Chaetoceros sp. were determined in this study. Thedaily rhythm and the influence of light and temperature on the production rate of DOC and POC were stud-ied by growing the diatom under different laboratory controlled conditions of light and temperature. Theresults showed that the production of DOC and POC varied with light and temperature and were generallyhigher at daytime than at night. Under culture conditions of 24L:0D light cycle and 3500 lx light intensi-ty, the DOC and POC reached maximum (DOC: 17. 27 mgC/L; POC: 103. 10 mgC/L). While

Simultaneous Growth of <i>Chaetoceros muelleri</i>and Bacteria in Batch Cultures

The relationship between bacterial load and the microalga Chaetoceros muelleri was analyzed in a scale-up experiment. The microalga was grown during five days in a 0.4-L Erlenmeyer flask, 2-L Fernbach flask, 18-L Carboy and 400-L column, during which the cell density of C. muelleri, the abundance of heterotrophic bacteria, Vibrio spp., and total bacteria were determined. The highest specific growth rates (μ) of C. muelleri occurred during the first day of culture (0.88 to 2.29 d-1). Highest cell density was recorded on the fifth day at the 2-L (7.62 × 106 cells·mL-1) and 18-L (6.32 × 106 cells·mL-1), coinciding with the maximum counts of heterotrophic bacteria (16.55 × 105 and >30 × 105 CFU·mL-1, respectively). There was a high correlation (0.80, 0.75, 0.85;p?5 cells·mL-1) during the five days occurred at 18-L Carboy. The concentration of total bacteria at all levels was always higher than that of heterotrophic bacteria. The average ratio of heterotrophic to total bacteria was higher in the 2-L (0.0108) and 18-L (0.0172) cultures. The high biomass of C. muelleri and the presence of Vibrio spp. at the 18-L and 400-L levels indicate that it is necessary to establish programs to prevent diseases and economic losses caused by pathogenic bacteria in penaeid shrimp farming.

纤细角毛藻培养条件优化

采用正交实验的方法 ,对影响纤细角毛藻(Chaetocerosgracilis)生长的主要营养因素进行了优化 ,获得了以海水为基础的优化培养基配方 :NaHCO30.15g/L,Na2SiO3(9H2O0.20g/L,NaNO31.00g/L,KH2PO40.02g/L,VB12.7mg/L,VB121.5μg/L。实验表明 ,用该优化配方培养纤细角毛藻具有生长速度快、产量高的显著优势 ,为该微藻在光生物反应器中的进一步高密度培养提供了良好条件。

两株硅藻筒柱藻和纤细角毛藻的油脂生产

通过气泡柱光反应器评价了两株硅藻筒柱藻(Cylindrotheca fusiformis)和纤细角毛藻(Chaetocerosgracilis)的生物量、油脂及甘油三脂的积累。结果发现,其生物量与油脂产率相当,脂肪酸组成方面,也均以C16:0和C16:1为主,但是筒柱藻的油脂组成以甘油三酯为主,纤细角毛藻的油脂以单酰甘油酯、磷脂和糖脂为主。通过培养条件的优化,发现相比于降低初始氮元素与硅元素,降低培养液盐度,能够获得更高的生物量、油脂以及甘油三脂产率。通过筒柱藻批次培养最高获得了0.36 g/(L.d)的甘油三脂产率,且甘三酯占收获干物质的50%以上,具有相当好的应用潜力。

Impacts of CO_2 enrichment on growth and photosynthesis in freshwater and marine diatoms

The physiological responses of Nitzschia palea Kvtzing, a freshwater diatom, to elevated CO2 were investigated and compared with those of a marine diatom, Chaetoceros muelleri Lemmermann previously reported. Elevated CO2 concentration to 700 μl/L increased the dissolved inorganic carbon （D!C） and lowered the pH in the cultures of N. palea, thus enhancing the growth by 4%-20% during the whole growth period. High CO2-grown N. palea cells showed lower levels of dark respiration rates and higher Ik values. Light-saturated photosynthetic rates and photosynthetic efficiencies decreased in N. palea with the doubling CO2 concentration in airflow to the bottom of cultures, although the doubling CO2 concentration in airflow to the surface cultures had few effects on these two photosynthetic parameters. N. palea cells were found to be capable of using HCO5 in addition to gaseous CO2, and the CO2 enrichment decreased their affinity for HCO5 and CO2. Although doubled CO2 level would enhance the biomass of N. patea and C. muelleri to different extents, compared with the marine diatom, it had a significant effect on the specific growth rates of N. palea. In addition, the responses of photosynthetic parameters of IV. palea to doubled CO2 concentration were almost opposite to those of C. muelleri.

Effect of Growth Phase on the Fatty Acid Compositions of Four Species of Marine Diatoms

The fatty acid compositions of four species of marine diatoms (Chaetoceros gracilis MACC/B13, Cylindrotheca fusiformis MACC/B211, Phaeodactylum tricornutum MACC/B221 and Nitzschia closterium MACC/B222), cultivated at 22 ℃± 1 ℃ with the salinity of 28 in f/2 medium and harvested in the exponential growth phase, the early stationary phase and the late stationary phase, were determined. The results showed that growth phase has significant effect on most fatty acid contents in the four species of marine diatoms. The proportions of 16:0 and 16:1n-7 fatty acids increased while those of 16:3n-4 and eicosapentaenoic acid (EPA) decreased with increasing culture age in all species studied. The subtotal of saturated fatty acids (SFA) increased with the increasing culture age in all species with the exception of B13. The subtotal of monounsaturated fatty acids (MUFA) increased while that of polyunsaturated fatty acids (PUFA) decreased with culture age in the four species of marine diatoms. MUFA reached their lowest value in the exponential growth phase, whereas PUFA reached their highest value in the same phase.

A Comparative Study of the Sensitivity of F_v/F_m to Phosphorus Limitation on Four Marine Algae

We studied the effects of nitrogen （N） and phosphorus （P） supply on Fv/Fm （maximal quantum yield of photosystem Ⅱ） in the algae Chaetoceros debilis, Dicrateria inornata, Platymonas subcordiformis and Heterosigma akashiwo to determine the sensitivity of Fv/Fm to P-limitation of the four species. Obvious decrease of Fv/Fm value was monitored in periods of P-depletion, the decrease showing different magnitudes among algal species. A more clear decrease of Fv/Fm in Platymonas subcordiformis and Heterosigma akashiwo was observed, compared with that in Chaetoceros debilis and Dicrateria inornata. After the re-supply of P, the index Fv/Fm of the four species all recovered quickly in 24h. Cell division was maintained and chlorophyll content continued to increase until the end of the experiment in Platymonas subcordiformis and Heterosigma akashiwo, while in Chaetoceros debilis and Dicrateria inornata, the division stopped in the later period when the growth of organisms came into the stationary phase. The most obvious respond of chlorophyll content to P-additions was observed in Heterosigma akashiwo culture in 24 h. The sensitivity of Fv/Fm to nutrient limitations is different among algal species, and much should be done to improve the application of this index.

氮、磷供给水平对纤细角毛藻生长及细胞物质组成的影响

纤细角毛藻(Chaetoceros gracilis)具有丰富的营养组成,是重要的生物饵料微藻。该试验以f/2培养基中标准的氮磷供给水平为基准,进行不同氮磷供给水平对纤细角毛藻生长及细胞物质组成的研究。结果表明,基准浓度的1/2倍及以下的低氮供给使纤细角毛藻的生物量减少严重,而基准浓度的2倍、3倍高氮供应下仍与基准氮供给相差不大。高于基准磷浓度供给促进纤细角毛藻的生长,其中基准磷浓度的3/2倍最优。在提高纤细角毛藻生物量产量方面,改变磷供给浓度比氮更有效。在细胞物质组成方面,基准浓度的3/2-3倍的高氮供给是提升细胞蛋白质含量的有效手段,而磷浓度变化对蛋白质含量的影响较低。细胞总糖含量的提升可通过降低磷供给水平(1/8-1倍基准浓度)实现。降低氮供应至基准浓度的1/8~1/4倍或者降低磷供应至基准浓度的1/8~1/4倍的寡营养条件,均能有效提高细胞脂肪含量,其中1/8倍的磷供给浓度对于提高脂肪含量效果最好。综合而言,纤细角毛藻的生长和细胞物质组成受磷营养供给的影响大于氮供给。

Isolation, characterization and implications of the bacterial communities associated with established cultures of Chattonella marina(Raphidophyceae) and Skeletonema costatum(Bacillariophyceae)

Cultivable bacteria coexisting in the cultures of two microalgal species, Chattonella marina(Raphidophyceae)and Skeletonema costatum(diatom, Bacillariophyceae), which have been maintained in the laboratory for several years, were examined in this study. Forty-eight and thirty-four cultivable bacterial strains were isolated from different growth stages of C. marina and S. costatum cultures, respectively. A total of twelve unique bacterial phylotypes were isolated. These bacterial phylotypes belonged to Alphaproteobacteria, Gammaproteobacteria,Bacteroidetes, and Actinobacteria. Alphaproteobacteria predominated in phycospheres of both microalgae, and Rhodobacteraceae was the most common family. Bacterial phylotypes were more diversified in cultures of S.costatum than in those of C. marina. Bacterial concentrations increased remarkably after the late stationary phase of C. marina, which might account for the decline in algal cells. One phylotype of S. costatum-associated bacteria had inhibitory effects on Chaetoceros curvisetus(Bacillariophyceae). However, most bacterial phylotypes from cultures of C. marina showed significant inhibition of the growth of C. curvisetus. The results suggested that bacteria associated with C. marina might have some ecological roles in its competition with diatoms.

Automatic cell object extraction of red tide algae in microscopic images

Extracting the cell objects of red tide algae is the most important step in the construction of an automatic microscopic image recognition system for harmful algal blooms.This paper describes a set of composite methods for the automatic segmentation of cells of red tide algae from microscopic images.Depending on the existence of setae,we classify the common marine red tide algae into non-setae algae species and Chaetoceros,and design segmentation strategies for these two categories according to their morphological characteristics.In view of the varied forms and fuzzy edges of non-setae algae,we propose a new multi-scale detection algorithm for algal cell regions based on border-correlation,and further combine this with morphological operations and an improved GrabCut algorithm to segment single-cell and multicell objects.In this process,similarity detection is introduced to eliminate the pseudo cellular regions.For Chaetoceros,owing to the weak grayscale information of their setae and the low contrast between the setae and background,we propose a cell extraction method based on a gray surface orientation angle model.This method constructs a gray surface vector model,and executes the gray mapping of the orientation angles.The obtained gray values are then reconstructed and linearly stretched.Finally,appropriate morphological processing is conducted to preserve the orientation information and tiny features of the setae.Experimental results demonstrate that the proposed methods can effectively remove noise and accurately extract both categories of algae cell objects possessing a complete shape,regular contour,and clear edge.Compared with other advanced segmentation techniques,our methods are more robust when considering images with different appearances and achieve more satisfactory segmentation effects.