This research studied the seasonal and spatial dynamics for abundance of picophytoplanktons (including Prochlorococcus spp., Synechococcus spp. and picoeukaryotes) in the South China Sea (SCS) and the Kuroshio. Waters were collected during five cruises between August 2009 and December 2010. Growth rates were determined in two size fractioned waters, <2 um and <10 um, after incubation. The differences of growth rates between the two size fractions were defined as the grazing rates. Before the incubation, waters were enriched with FeCl3, EDTA, or NH4Cl to examine the possible shortage of Fe or nitrogen. Abundances of picophytoplanktons and nanoflagellates were examined using a flow-cytometry and a microscope, respectively. Prochlorococcus was more abundant in the warm than the cold seasons and in the Kuroshio and the basin of the SCS than in the shelf and slope of the SCS. In the high abundance seasons/regions, low irradiance enhanced the growth rates of Prochlorococcus. Although both of the growth rates and grazing rates were high during then, the growth rates were found higher than the grazing rates. Addition of EDTA enhanced the growth rates that was likely attributed to its chelating with toxic trace metals (such as Cd2+, Cd2+) and/or with growth necessity trace metals (such as Co2+). The seasonal/spatial distributions for Synechococcus were in contrast to that of Prochlorococcus. High growth rates of Synechococcus were related to high nitrate concentrations and the low irradiance. The growth rates were higher than the grazing rates in the high nitrogen seasons/regions when/where irradiance was also relatively low. EDTA also enhanced the growth of Synechococcus, and was likely due to its chelating to remove Cd2+ and/or to retain Co2+. Distributions of picoeukaryotes were similar to that of Synechococcus. Factors affected its dynamics were not clear because of its complicated compositions.

Synechococcus elongatus PCC 7942 is a model organism used to study the circadian rhythm, a process that is driven by an endogenous biological clock that can be modulated by external cues such as light and temperature. Some proteins have been identified that are involved in circadian signal transduction in S. elongatus. Of them, KaiA, KaiB and KaiC comprise the central oscillator components, which are essential for internal timekeeping. SasA is an important protein in the output pathway, which passes the information from central oscillator to downstream components, and thus controls metabolic and behavioral processes. CikA is a major component in the input pathway, which maintains synchrony of the oscillator with the environment. CikA is an unusual phytochrome-like histidine protein kinase. It has a pseudo receiver domain which can not accept a phosphoryl group. CikA is thought to be located at the poles of the cell through interaction between PsR and some protein or protein complex that is also localized at the poles. One of the potential CikA-interacting proteins identified through a yeast two hybrid screen is called hypothetical protein 1. It specifically recognizes a PsR bait in a yeast two hybrid assay. A bioinformatics analysis showed that there are predicted signal peptide and transmembrane domains at the N-terminal and a cytochrome C homolog domain at the C-terminal of Hyp1. Elucidating the features and function of Hyp1 will provide us with useful information to understand the function and working mechanism of CikA, and therefore will help us to clarify the signal transduction in the clock. In this research, I used genetic, cell biological and biochemical approaches to study the features and function of this newly identified clock component Hyp1. To confirm the interaction between PsR and Hyp1 and complement the yeast two hybrid data, I truncated Hyp1 (Thyp1) and purified soluble Thyp1. At the same time, I obtained purified PsR. I tried to copurify the PsR and 6-histidine-tagged Hyp1 on a nickel affinity column. However, PsR non-specifically bound to the column, which eliminated the utility of this approach to study their interaction. In addition to using a biochemical approach to study Hyp1, I constructed three hyp1 overexpression alleles for genetic analysis and two hyp1-yfp overexpression fusion alleles for subcellular localization studies. All of them will help us to understand the features and function of Hyp1.

Bochum, Univ., Diss., 2003. / Computerdatei im Fernzugriff.

Bochum, Universiẗat, Diss., 2003.

Techn. University, Diss., 2004--Berlin.

Techn. University Diss., 2005--Berlin.

Les picocyanobactéries marines sont les organismes photosynthétiques les plus abondants de la planète. Parmi celles-ci, les Synechococcus marins sont détectés de l’équateur aux cercles polaires, suggérant qu’ils ont évolué des stratégies adaptatives très efficaces à la température. La première partie de ce travail de thèse a visé à étudier la thermophysiologie de différentes lignées de la radiation des Synechococcus marins. Les résultats d’expériences de variations thermiques à court et long terme associées à une étude de phyloécologie ont démontré l’existence de clades physiologiquement spécialisées dans des niches thermiques distinctes, i.e des thermotypes. Ces travaux ont de plus mis en évidence l’importance de l’optimisation de l’efficacité de l’appareil photosynthétique dans l’acclimatation à la température. Ainsi, la thermostabilité du photosystème II, complexe clé de la régulation de l’énergie, a été comparée chez différentes souches de Synechococcus marins. Ces travaux ont révélé de grandes différences de thermostabilité de l’antenne photosynthétique et de ses constituants, qui sont corrélées à la latitude d’isolement des souches. L’étude de modèles d’homologie de structure de phycobiliprotéines a permis de révéler certaines des adaptations moléculaires de ce complexe à la température. La fonctionnalité des complexes photosynthétiques est directement dépendante de la fluidité des membranes au sein desquelles ils sont insérés, un facteur physique très influencé par la température. Le troisième volet de cette thèse a permis de mieux comprendre les mécanismes de régulation des lipides membranaires chez les Synechococcus marins. Les résultats montrent que la composition en acides gras joue un rôle important durant l’acclimatation à différentes températures. De plus, par une approche de génomique comparative, ce travail de thèse montre que les Synechococcus marins présentent des équipements différents en enzymes désaturases, qui ont très probablement joué un rôle dans la colonisation de différentes niches thermiques. Les résultats de ce travail de thèse, discutés dans un contexte d’évolution de l’adaptation au gradient latitudinal de température chez les picocyanobactéries marines, soulèvent de nouvelles hypothèses exaltantes pour les travaux futurs. / Marine picocyanobacteria are the most abundant photosynthetic organisms on Earth. Among them, Synechococcus displays a wide latitudinal distribution, ranging from the equator to polar circles, suggesting that they have evolved efficient adaptive strategies to cope with the latitudinal temperature gradient. The first part of this PhD work aimed at studying the thermophysiology of different lineages of the marine Synechococcus radiation. The combination of thermal acclimation and stress experiments with a phyloecology study allowed unveiling the existence of lineages physiologically specialized in distinct thermal niches, i.e. thermotypes. This work furthermore pointed out the importance of the capacities to optimize the photosynthetic apparatus efficiency for successful temperature acclimation. The thermostability of photosystem II, a key complex to the regulation of light energy utilisation, was compared within several marine Synechococcus strains. The results revealed that the photosynthetic antenna and its components have distinct thermostabilities, which are related to the strain isolation latitude. Structural homology models of phycobiliproteins thus revealed sites of molecular adaptation of the antenna to temperature. The function of the photosynthetic complexes is dependent on the fluidity of the membranes in which they are embedded, a physical factor regulated by temperature. The results a first lipidomic study suggested that the regulation of the composition in acyl chains plays an important role in temperature acclimation in marine Synechococcus. Furthermore, genomic comparative analyses revealed notably that marine Synechococcus have distinct sets of desaturase enzymes which have likely played a role in the colonization of different thermal niches. The results of this PhD thesis, which are discussed in the context of the Synechococcus adaptive evolution to the latitudinal gradient of temperature, raise new hypotheses for some future exciting work.

Synechococcus, a genus of photosynthetic cyanobacteria, is the second most abundant oxygenic microorganism in the marine environment that contributes significantly to the ocean’s primary productivity (Humily et al. 2013; Shukla et al. 2012). They are capable of utilizing available light of different wavelengths in the visible spectrum to perform photosynthesis and fix carbon dioxide and thus inhabit a wide range of light niches in the ocean along horizontal (coast vs offshore) and vertical gradients (depth) (Humily et al. 2013). A gene encoding a putative lyase isomerase, mpeQ, is present in phycoerythrin-II encoding operon that is expressed constitutively and a gene encoding putative lyase, mpeW, is present in CA-4 genomic island whose expression is regulated by ambient light color were identified and characterized in Synechococcus sp. A15- 62, a strain having a blue light specialist phenotype in its basal state. The amino acid sequence of the proteins encoded by mpeW and mpeQ are similar to other characterized lyases and these genes are conserved in cyanobacteria strains containing the CA4-B genomic island, which controls CA4 (Humily et al. 2013). The MpeW and MpeQ proteins were produced in E. coli and co-expressed with recombinant HT-MpeA and phycoerythrobilin (PEB) synthesis machinery. Site directed mutants of the HT-MpeA protein (Cys75Ala, Cys83Ala, Cys140Ala) were used to investigate the site for bilin attachment. The recombinant protein co-expression experiments of MpeQ and MpeW demonstrated that MpeQ attaches phycoerythrobilin (PEB) to cysteine-83 site on a-phycoerythrin II and isomerizes it to phycourobilin (PUB) and MpeW attaches phycoerythrobilin (PEB) to the same site.

Areally expansive, persistent and recurring blooms frequently dominated by cyanobacteria have developed primarily in the north-central region of Florida Bay since approximately 1991. This part of the bay has a history of the following: periodic hypersalinity, high sediment-derived turbidity, P limitation, N limitation, light limitation and long water residence time. Clonal isolates of selected dominant bloom species of cyanobacteria (Synechococcus cf. elongatus and Synechocystis sp.) and diatoms (Chaetoceros cf. salsugineus and Thalassiosira cf. oceanica) from Florida Bay were examined in an effort to explain their relative dominance of the phytoplankton community. The following physiological characteristics and nutrient strategies of the study species were examined: (1) salinity-growth response; (2) light-growth response; (3) phosphorus-dependent growth kinetics; (4) ERC-theory phosphorus competitiveness; (5) cellular quotas and luxury storage capabilities of N and P; (6) optimal N:P ratios; (7) P and N-limited competitiveness under various salinities, N:P ratios, forms of N and P, and rates of nutrient delivery; (8) aerobic nitrogen fixation; (9) production of allelochemic compounds, and (10) response to resuspended sediment. This study identified salinity and nutrient limitation as the factors having the greatest potential to regulate the development of cyanobacteria and diatom bloom dominance in Florida Bay. The results strongly suggest that the frequent dominance of Synechococcus cf. elongatus, and Synechocystis sp. in the recurring phytoplankton blooms of the north-central region of Florida Bay can be attributed to their superior P-competitiveness and to a lesser degree to their greater salinity tolerance limits.

Population dynamics of picophytoplanktons, including Prochlorococcus, Synechococcus, and picoeukaryotes, were investigated in the upstream Kuroshio. Data were collected during eight cruises between July 2007 and May 2009. Sampling stations were located along 21¢X55¡¦N and between 121¢X00¡¦E and 122¢X10¡¦E in the Kuroshio off the Southeast Taiwan. Monitoring experiments including light shadding experiment, nutrient enrichment, temperature control, and grazing experiments were conducted to better understand the mechanisms that affect the growths of the picophytoplanktons. The abundances of the picophytoplanktons were measured using a flow cytometry.Water column integrated (0~200 m) abundance of Prochlorococcus was higher (26.63 ¡Ó 3.87 ¡Ñ 1012 cells m-2) in spring than either summer (19.07 ¡Ó 4.08 ¡Ñ 1012 cells m-2), autumn (16.05 ¡Ó 2.80 ¡Ñ 1012 cells m-2), or winter (17.89 ¡Ó 5.41 ¡Ñ 1012 cells m-2). During winter, the abundance was significantly (p<0.05) higher at the offshore station (17.89 ¡Ó 5.41 ¡Ñ 1012 cells m-2) than the inshore station (3.19 ¡Ó 2.07 ¡Ñ 1012 cells m-2). The abundance of Prochlorococcus was positively related to water temperature, nitracline depth (Dni), and euphotic depth (Deu), and negatively to surface concentration of N+N or SRP. Prochlorococcus was abundant (>100 ¡Ñ 103 cells ml-1) in the upper 100-m water column. Its maximum (200~300 ¡Ñ 103 cells ml-1) often occurred at the depth shallower than 75 m. The cell density sustained at >25 ¡Ñ 103 cells ml-1 between 100~150 m and was almost nil at the depth deeper than 150 m. There was no significant seasonal differences for either the abundances of Synechococcus (0.32~1.07 ¡Ñ 1012 cells m-2) or picoeukaryotes (0.16~0.24 ¡Ñ 1012 cells m-2). During winter, the abundances of Synechococcus was significantly (p<0.05) higher in the offshore Kuroshio water (2.94 ¡Ó 0.32 ¡Ñ 1012 cells m-2) than that of the inshore Kuroshio water. Similar trend of offshore (0.52 ¡Ó 0.05 ¡Ñ 1012 cells m-2) higher than the inshore was observed for picoeukaryotes in winter. The dynamics of Synechococcus abundance was positively related to surface SRP concentration and negatively to Dni. The picoeukaryotes abundance was positively related to surface N+N concentration, and SRP and negatively to Temp, Dni, and Deu. Vertical distribution of Synechococcus showed that the maximum abundance often occurred above 75 m, but was almost nil below 100 m. By contrast, the maximum abundance for picoeukaryotes often occurred between 50~125 m. The abundance of Synechococcus was positively related to the abundance of picoeukaryotes. And their abundance were negatively related to that of Prochlorococcus. Many environmental factors fluctualed parallelly. Dynamics of surface Temp, Dni and Deu were positively correlated to each other and either of them was negatively correlated to the dynamics of surface concentration of N+N or SRP. Surface N+N was positively correlated with surface SRP. The result of light shadding experiment showed that Prochlorococcus and picoeukaryotes, compared to Synechococcus, were much sensitive to high intensity of light. This suggest that Synechococcus was more tolerant to high light intensity or required more light energy than Prochlorococcus or picoeukaryotes. The results of nutrient enrichment experiments showed that addition of EDTA significantly enhanced the growth of three groups of picophytoplanktons. However, there was no significant difference after addition of either nitrate, Fe, or Cu. Prochlorococcus grew better at 27 ¢XC than 30 ¢XC in the temperature experiment. But there was no difference in the growth rate between 27 ¢XC and 30 ¢XC for Synechococcus or picoeukaryotes The result of grazing experiment showed that there was no difference between the growth rate with and without grazers in the incubation for any of the three groups of picophytoplanktons.