Browsing by Author "Dassow, Peter von"

Now showing 1 - 20 of 41
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    Calcifying phytoplankton in natural laboratories for understanding ocean acidification
    (2021) Díaz Rosas, Francisco Javier; Dassow, Peter von; Pontificia Universidad Católica de Chile. Facultad de Ciencias Biológicas
    Los cocolitofóridos son organismos fitoplanctónicos unicelulares caracterizados por una cobertura de placas de calcita, los cocolitos, que son producidos dentro de la célula. Estos calcificadores, como uno de los principales grupos funcionales planctónicos, juegan un rol importante en el ciclo del carbono inorgánico y posiblemente como lastre hundiendo carbono orgánico hacia el océano profundo. La mayoría de los esfuerzos para entender las respuestas de los cocolitofóridos hacia la acidificación del océano (AO) –o el aumento del CO2 atmosférico reduce el pH y estado de saturación (Ω) de CaCO3 del océano– ha sido a través de experimentos de laboratorio, principalmente usando un pequeño set de cepas de la especie más cosmopolita y fácilmente cultivable Emiliania huxleyi. Esta especie resulta particularmente interesante ya que es joven (~ 291.000 años) y se ha adaptado a un amplio rango de ambientes marinos. Sin embargo, este no es el único cocolitofórido y aun dentro de esta especie hay mucha diversidad fenotípica y genética y respuestas diversas hacia la AO en el laboratorio. A pesar de los esfuerzos realizados aun no es claro como los efectos fisiológicos bajo condiciones controladas se trasladan a respuestas de campo a nivel de comunidad. Esta tesis buscó contribuir a entender este asunto estudiando la distribución, composición y nicho realizado de ensambles de cocolitofóridos y morfotipos de E. huxleyi en ambientes con niveles contrastantes de pCO2/pH/Ωcalcita del Pacífico Sureste, y evaluar las respuestas de diferentes morfotipos de E. huxleyi a niveles de pCO2/pH ajustados en el laboratorio. Para esto, se muestrearon los cocolitofóridos en una sección costera-oceánica, aguas mesotróficas, sistemas de surgencia, y fiordos-canales de Patagonia. De un total de 40 especies, E. huxleyi fue la más prevalente (30-100 % abundancia relativa). Dentro de este taxón, varios morfotipos han sido descritos como estables en cultivo y diferenciados genéticamente (e.g., los morfotipos A y R). El morfotipo A moderadamente-calcificado dominó las poblaciones de E. huxleyi siendo sólo superado por el morfotipo R altamente-calcificado en sistemas de surgencia con alto pCO2/bajo pH. Este cambio abrupto en composición de las poblaciones de E. huxleyi sugirió que estos ambientes costeros mantienen reservorios genéticos para su adaptación a la AO. Por consiguiente, se probó la hipótesis que aquellas formas están adaptados para resistir condiciones de alto pCO2/bajo pH. Inesperadamente, los morfotipos del Pacífico Sureste no fueron más sensibles que las cepas altamente-calcificadas desde aguas contiguas con alto pCO2/bajo pH (disminuyeron las tasas de crecimiento y razón PIC/POC). Por otro lado, análisis de nicho realizado mostraron que el morfotipo A posee un nicho más amplio y tolerante a cambios ambientales (i.e., generalista) que el nicho del morfotipo R, especializado en aguas con alto pCO2/bajo pH. La falta de evidencia de adaptación local a condiciones de alto pCO2/bajo pH en E. huxleyi, podría ser explicado por una estrecha respuesta unimodal hacia Ωcalcita revelado por el análisis de nicho que no fue testeado experimentalmente. Alternativamente, el morfotipo R altamente-calcificado podría ser seleccionado por una condición particular del Pacífico Sureste no identificada que se correlaciona con temperatura, salinidad y Ωcalcita de su nicho realizado. En suma, a pesar de poseer rápidas tasas de reemplazo y grandes tamaños poblacionales, organismos planctónicos oceánicos no necesariamente exhiben adaptaciones a la surgencia de aguas con alto CO2, y este ubicuo cocolitofórido podría estar cerca del límite de su capacidad para adaptar a la AO en curso.
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    Developing and implementing an effective public outreach program
    (2009) Harrison, J.; Dassow, Peter von
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    Differential responses of Emiliania huxleyi (Haptophyta) strains to copper excess
    (2018) Mella Flores, Daniella Andrea; Machon, Julia; Contreras Porcía, Loretto Matilde; Mesa Campbell, Sabina; Dassow, Peter von
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    Emiliania huxleyi endures N-limitation with an efficient metabolic budgeting and effective ATP synthesis
    (2014) Rokitta, Sebastian D.; Dassow, Peter von; Rost, Björn.; John, Uwe.
    Abstract Background Global change will affect patterns of nutrient upwelling in marine environments, potentially becoming even stricter regulators of phytoplankton primary productivity. To better understand phytoplankton nutrient utilization on the subcellular basis, we assessed the transcriptomic responses of the life-cycle stages of the biogeochemically important microalgae Emiliania huxleyi to nitrogen-limitation. Cells grown in batch cultures were harvested at ‘early’ and ‘full’ nitrogen-limitation and were compared with non-limited cells. We applied microarray-based transcriptome profilings, covering ~10.000 known E. huxleyi gene models, and screened for expression patterns that indicate the subcellular responses. Results The diploid life-cycle stage scavenges nitrogen from external organic sources and -like diatoms- uses the ornithine-urea cycle to rapidly turn over cellular nitrogen. The haploid stage reacts similarly, although nitrogen scavenging is less pronounced and lipid oxidation is more prominent. Generally, polyamines and proline appear to constitute major organic pools that back up cellular nitrogen. Both stages induce a malate:quinone-oxidoreductase that efficiently feeds electrons into the respiratory chain and drives ATP generation with reduced respiratory carbon throughput. Conclusions The use of the ornithine-urea cycle to budget the cellular nitrogen in situations of limitation resembles the responses observed earlier in diatoms. This suggests that underlying biochemical mechanisms are conserved among distant clades of marine phototrophic protists. The ornithine-urea cycle and proline oxidation appear to constitute a sensory-regulatory system that monitors and controls cellular nitrogen budgets under limitation. The similarity between the responses of the life-cycle stages, despite the usage of different genes, also indicates a strong functional consistency in the responses to nitrogen-limitation that appears to be owed to biochemical requirements. The malate:quinone-oxidoreductase is a genomic feature that appears to be absent from diatom genomes, and it is likely to strongly contribute to the uniquely high endurance of E. huxleyi under nutrient limitation.
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    Genetic tool development in marine protists: emerging model organisms for experimental cell biology
    (2020) Faktorová, Drahomíra; Nisbet, R. Ellen R.; Fernández Robledo, José A.; Casacuberta, Elena; Sudek, Lisa; Allen, Andrew E.; Ares, Manuel, 1955-; Federici, Fernán; Jorge Ibañez, Jorge; Dassow, Peter von
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    Identification of the meiotic toolkit in diatoms and exploration of meiosis-specific SPO11 and RAD51 homologs in the sexual species Pseudo-nitzschia multistriata and Seminavis robusta
    (2015) Patil, Shrikant.; Dassow, Peter von; Moeys, Sara.; Huysman, Marie J. J.; Mapleson, Daniel.; De Veylder, Lieven.; Sanges, Remo.; Vyverman, Wim.; Montresor, Marina.; Ferrante, Maria I.
    Abstract Background Sexual reproduction is an obligate phase in the life cycle of most eukaryotes. Meiosis varies among organisms, which is reflected by the variability of the gene set associated to the process. Diatoms are unicellular organisms that belong to the stramenopile clade and have unique life cycles that can include a sexual phase. Results The exploration of five diatom genomes and one diatom transcriptome led to the identification of 42 genes potentially involved in meiosis. While these include the majority of known meiosis-related genes, several meiosis-specific genes, including DMC1, could not be identified. Furthermore, phylogenetic analyses supported gene identification and revealed ancestral loss and recent expansion in the RAD51 family in diatoms. The two sexual species Pseudo-nitzschia multistriata and Seminavis robusta were used to explore the expression of meiosis-related genes: RAD21, SPO11-2, RAD51-A, RAD51-B and RAD51-C were upregulated during meiosis, whereas other paralogs in these families showed no differential expression patterns, suggesting that they may play a role during vegetative divisions. An almost identical toolkit is shared among Pseudo-nitzschia multiseries and Fragilariopsis cylindrus, as well as two species for which sex has not been observed, Phaeodactylum tricornutum and Thalassiosira pseudonana, suggesting that these two may retain a facultative sexual phase. Conclusions Our results reveal the conserved meiotic toolkit in six diatom species and indicate that Stramenopiles share major modifications of canonical meiosis processes ancestral to eukaryotes, with important divergences in each Kingdom.Abstract Background Sexual reproduction is an obligate phase in the life cycle of most eukaryotes. Meiosis varies among organisms, which is reflected by the variability of the gene set associated to the process. Diatoms are unicellular organisms that belong to the stramenopile clade and have unique life cycles that can include a sexual phase. Results The exploration of five diatom genomes and one diatom transcriptome led to the identification of 42 genes potentially involved in meiosis. While these include the majority of known meiosis-related genes, several meiosis-specific genes, including DMC1, could not be identified. Furthermore, phylogenetic analyses supported gene identification and revealed ancestral loss and recent expansion in the RAD51 family in diatoms. The two sexual species Pseudo-nitzschia multistriata and Seminavis robusta were used to explore the expression of meiosis-related genes: RAD21, SPO11-2, RAD51-A, RAD51-B and RAD51-C were upregulated during meiosis, whereas other paralogs in these families showed no differential expression patterns, suggesting that they may play a role during vegetative divisions. An almost identical toolkit is shared among Pseudo-nitzschia multiseries and Fragilariopsis cylindrus, as well as two species for which sex has not been observed, Phaeodactylum tricornutum and Thalassiosira pseudonana, suggesting that these two may retain a facultative sexual phase. Conclusions Our results reveal the conserved meiotic toolkit in six diatom species and indicate that Stramenopiles share major modifications of canonical meiosis processes ancestral to eukaryotes, with important divergences in each Kingdom.Abstract Background Sexual reproduction is an obligate phase in the life cycle of most eukaryotes. Meiosis varies among organisms, which is reflected by the variability of the gene set associated to the process. Diatoms are unicellular organisms that belong to the stramenopile clade and have unique life cycles that can include a sexual phase. Results The exploration of five diatom genomes and one diatom transcriptome led to the identification of 42 genes potentially involved in meiosis. While these include the majority of known meiosis-related genes, several meiosis-specific genes, including DMC1, could not be identified. Furthermore, phylogenetic analyses supported gene identification and revealed ancestral loss and recent expansion in the RAD51 family in diatoms. The two sexual species Pseudo-nitzschia multistriata and Seminavis robusta were used to explore the expression of meiosis-related genes: RAD21, SPO11-2, RAD51-A, RAD51-B and RAD51-C were upregulated during meiosis, whereas other paralogs in these families showed no differential expression patterns, suggesting that they may play a role during vegetative divisions. An almost identical toolkit is shared among Pseudo-nitzschia multiseries and Fragilariopsis cylindrus, as well as two species for which sex has not been observed, Phaeodactylum tricornutum and Thalassiosira pseudonana, suggesting that these two may retain a facultative sexual phase. Conclusions Our results reveal the conserved meiotic toolkit in six diatom species and indicate that Stramenopiles share major modifications of canonical meiosis processes ancestral to eukaryotes, with important divergences in each Kingdom.Abstract Background Sexual reproduction is an obligate phase in the life cycle of most eukaryotes. Meiosis varies among organisms, which is reflected by the variability of the gene set associated to the process. Diatoms are unicellular organisms that belong to the stramenopile clade and have unique life cycles that can include a sexual phase. Results The exploration of five diatom genomes and one diatom transcriptome led to the identification of 42 genes potentially involved in meiosis. While these include the majority of known meiosis-related genes, several meiosis-specific genes, including DMC1, could not be identified. Furthermore, phylogenetic analyses supported gene identification and revealed ancestral loss and recent expansion in the RAD51 family in diatoms. The two sexual species Pseudo-nitzschia multistriata and Seminavis robusta were used to explore the expression of meiosis-related genes: RAD21, SPO11-2, RAD51-A, RAD51-B and RAD51-C were upregulated during meiosis, whereas other paralogs in these families showed no differential expression patterns, suggesting that they may play a role during vegetative divisions. An almost identical toolkit is shared among Pseudo-nitzschia multiseries and Fragilariopsis cylindrus, as well as two species for which sex has not been observed, Phaeodactylum tricornutum and Thalassiosira pseudonana, suggesting that these two may retain a facultative sexual phase. Conclusions Our results reveal the conserved meiotic toolkit in six diatom species and indicate that Stramenopiles share major modifications of canonical meiosis processes ancestral to eukaryotes, with important divergences in each Kingdom.
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    Impact of low pH/high pCO2 on the physiological response and fatty acid content in diatom Skeletonema pseudocostatum
    (2017) Jacob, Barbara G.; Dassow, Peter von; Salisbury, Joe E.; Navarro, Jorge M.; Vargas, Cristian A.
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    Impacts of reduced inorganic N:P ratio on three distinct plankton communities in the Humboldt upwelling system
    (2019) Spilling, K.; Camarena-Gómez, M. T.; Lipsewers, T.; Martinez-Varela, A.; Díaz-Rosas, F.; Eronen-Rasimus, E.; Silva, N.; Dassow, Peter von; Montecino, V.
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    In search of new tractable diatoms for experimental biology
    (2008) Chepurnov, VA.; Dassow, Peter von
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    Life-cycle modification in open oceans accounts for genome variability in a cosmopolitan phytoplankton
    (2015) Dassow, Peter von; Mella Flores, Daniella Andrea; Herrera Tello, Yeritza Romainne