Browsing by Author "John, Uwe"

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    Impact of Nitrogen Sources on Gene Expression and Toxin Production in the Diazotroph Cylindrospermopsis raciborskii CS-505 and Non-Diazotroph Raphidiopsis brookii D9
    (2014) Stucken, Karina; John, Uwe; Cembella, Allan; Soto-Liebe, Katia; Vasquez, Monica
    Different environmental nitrogen sources play selective roles in the development of cyanobacterial blooms and noxious effects are often exacerbated when toxic cyanobacteria are dominant. Cylindrospermopsis raciborskii CS-505 (heterocystous, nitrogen fixing) and Raphidiopsis brookii D9 (non-N2 fixing) produce the nitrogenous toxins cylindrospermopsin (CYN) and paralytic shellfish toxins (PSTs), respectively. These toxin groups are biosynthesized constitutively by two independent putative gene clusters, whose flanking genes are target for nitrogen (N) regulation. It is not yet known how or if toxin biosynthetic genes are regulated, particularly by N-source dependency. Here we show that binding boxes for NtcA, the master regulator of N metabolism, are located within both gene clusters as potential regulators of toxin biosynthesis. Quantification of intra-and extracellular toxin content in cultures at early stages of growth under nitrate, ammonium, urea and N-free media showed that N-sources influence neither CYN nor PST production. However, CYN and PST profiles were altered under N-free medium resulting in a decrease in the predicted precursor toxins (doCYN and STX, respectively). Reduced STX amounts were also observed under growth in ammonium. Quantification of toxin biosynthesis and transport gene transcripts revealed a constitutive transcription under all tested N-sources. Our data support the hypothesis that PSTs and CYN are constitutive metabolites whose biosynthesis is correlated to cyanobacterial growth rather than directly to specific environmental conditions. Overall, the constant biosynthesis of toxins and expression of the putative toxin-biosynthesis genes supports the usage of qPCR probes in water quality monitoring of toxic cyanobacteria.
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    MICROEVOLUTIONARY VARIABILITY OF A COMPLEX LIFE CYCLE IN A COSMOPOLITAN MICROALGAE
    (TAYLOR & FRANCIS LTD, 2021) von Dassow, Peter; John, Uwe
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    Overcalcified forms of the coccolithophore Emiliania huxleyi in high CO2 waters are not pre-adapted to ocean acidification
    (2017) Dassow, Peter von; Díaz Rosas, Francisco Javier; Bendif, El-Mahdi; Gaitan-Espitia, Juan-Diego; Mella-Flores, Daniella; Rokitta, Sebastian; John, Uwe; Torres, Rodrigo
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    Pan genome of the phytoplankton Emiliania underpins its global distribution
    (2013) Read, Betsy A.; Kegel, Jessica; Klute, Mary J.; Kuo, Alan; Lefebvre, Stephane C.; Maumus, Florian; Mayer, Christoph; Miller, John; Monier, Adam; Salamov, Asaf; Young, Jeremy; Aguilar, Maria; Claverie, Jean-Michel; Frickenhaus, Stephan; Gonzalez, Karina; Herman, Emily K.; Lin, Yao-Cheng; Napier, Johnathan; Ogata, Hiroyuki; Sarno, Analissa F.; Shmutz, Jeremy; Schroeder, Declan; de Vargas, Colomban; Verret, Frederic; von Dassow, Peter; Valentin, Klaus; Van de Peer, Yves; Wheeler, Glen; Dacks, Joel B.; Delwiche, Charles F.; Dyhrman, Sonya T.; Gloeckner, Gernot; John, Uwe; Richards, Thomas; Worden, Alexandra Z.; Zhang, Xiaoyu; Grigoriev, Igor V.; Allen, Andrew E.; Bidle, Kay; Borodovsky, M.; Bowler, C.; Brownlee, Colin; Cock, J. Mark; Elias, Marek; Gladyshev, Vadim N.; Groth, Marco; Guda, Chittibabu; Hadaegh, Ahmad; Iglesias-Rodriguez, Maria Debora; Jenkins, J.; Jones, Bethan M.; Lawson, Tracy; Leese, Florian; Lindquist, Erika; Lobanov, Alexei; Lomsadze, Alexandre; Malik, Shehre-Banoo; Marsh, Mary E.; Mackinder, Luke; Mock, Thomas; Mueller-Roeber, Bernd; Pagarete, Antonio; Parker, Micaela; Probert, Ian; Quesneville, Hadi; Raines, Christine; Rensing, Stefan A.; Riano-Pachon, Diego Mauricio; Richier, Sophie; Rokitta, Sebastian; Shiraiwa, Yoshihiro; Soanes, Darren M.; van der Giezen, Mark; Wahlund, Thomas M.; Williams, Bryony; Wilson, Willie; Wolfe, Gordon; Wurch, Louie L.
    Coccolithophores have influenced the global climate for over 200 million years(1). These marine phytoplankton can account for 20 per cent of total carbon fixation in some systems(2). They form blooms that can occupy hundreds of thousands of square kilometres and are distinguished by their elegantly sculpted calcium carbonate exoskeletons (coccoliths), rendering them visible from space(3). Although coccolithophores export carbon in the form of organic matter and calcite to the sea floor, they also release CO2 in the calcification process. Hence, they have a complex influence on the carbon cycle, driving either CO2 production or uptake, sequestration and export to the deep ocean(4). Here we report the first haptophyte reference genome, from the coccolithophore Emiliania huxleyi strain CCMP1516, and sequences from 13 additional isolates. Our analyses reveal a pan genome (core genes plus genes distributed variably between strains) probably supported by an atypical complement of repetitive sequence in the genome. Comparisons across strains demonstrate that E. huxleyi, which has long been considered a single species, harbours extensive genome variability reflected in different metabolic repertoires. Genome variability within this species complex seems to underpin its capacity both to thrive in habitats ranging from the equator to the subarctic and to form large-scale episodic blooms under a wide variety of environmental conditions.