Browsing by Author "Ulloa, Osvaldo"
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- ItemCarbon assimilation by the picoplanktonic community inhabiting the secondary chlorophyll maximum of the anoxic marine zones of the eastern tropical north and south pacific(FRONTIERS MEDIA SA, 2022) Aldunate, Montserrat; Von Dassow, Peter; Vargas, Cristian A.; Ulloa, OsvaldoAnoxic marine zones (AMZs) constitute pelagic systems distinguished from the oxygen minimum zones (OMZs) by the complete absence of detectable oxygen and the accumulation of nitrite in mid-waters. At the top of the oxygen-depleted layer and below the oxycline, nutrients are abundant; light intensity is very much reduced (<1% of incident light) and a secondary chlorophyll maximum (SCM) is developed. The shoaling of the oxygen-depleted layer, product of the AMZ expansion, could enhance this SCM, which has little-known biogeochemical effects. Here, we show that the SCM is contributing a measurable signal in the particulate organic carbon (POC), enough to alter the δ13CPOC in the top of the oxygen-depleted layer. This data showed significant differences among stations with and without the development of a SCM, being 3.0‰ heavier when a SCM is developed, and indicating photosynthetic activity and/or remineralization in the top of the AMZ. More depleted δ13CPOC values were also found when no SCM was present indicating stronger chemoautotrophic activity, potentially driven by anammox and sulfur-oxidizing bacteria activity. Assimilation rate data show that when sufficient light and Prochlorococcus are present, photosynthesis exceeds chemoautotrophic carbon fixation, and can exceed heterotrophic assimilation of glucose or acetate. However, in the majority of the stations, assimilation rates of both glucose and acetate exceeded carbon fixation rates under light stimulation, suggesting that often the SCM is still a net heterotrophic system
- ItemCARBON ASSIMILATION IN THE COMMUNITY INHABITING THE SECONDARY CHLOROPHYLL MAXIMUM OF ANOXIC MARINE ZONES OF THE EASTERN TROPICAL PACIFIC OCEAN(TAYLOR & FRANCIS LTD, 2021) Aldunate, Montserrat; von Dassow, Peter; Vargas, Cristian A.; Ulloa, Osvaldo
- ItemDistinct oxygen environments shape picoeukaryote assemblages thriving oxygen minimum zone waters off central Chile(2020) De la Iglesia, Rodrigo; Echenique-Subiabre, Isidora; Rodriguez-Marconi, Susana; Pablo Espinoza, Juan; von Dassow, Peter; Ulloa, Osvaldo; Trefault, NicoleOxygen minimum zones (OMZs) support ocean biogeochemical cycles of global importance. The OMZ off central Chile is characterized by seasonally variable oxygen concentrations due to upwelling events. Bacterial and archaeal communities from this area have been previously described; however, picoeukaryote communities remain largely unexplored. In order to improve our knowledge on picoeukaryote ecology and the effect of controlling factors on its community structure, environmental parameters and 18S rRNA metabarcoding analyses were performed in water samples collected at several depths at a time series station on the continental shelf in March, May and August. Our results showed that oxygen, nitrate, silicate and temperature are relevant factors shaping the picoeukaryote community structure. Overall, according to our sequence dataset, the OMZ was dominated by Dinophyceae members including marine parasitic dinoflagellates. Moreover, dysoxic and suboxic conditions were enriched by fungi and phagotrophic protists from Ustilaginomycetes, Bicoecea and Choanoflagellatea. The latter is particularly relevant in the understanding of metazoan evolution and the origins of multicellularity in low-oxygen environments. Picoeukaryote communities changed significantly over the 3 months sampled with variations in water column stratification, including the occurrence of a winter bloom of Mamiellales. Altogether, this study reveals a great diversity and dynamics of picoeukaryotes inhabiting a coastal OMZ.
- ItemDistinctive archaeal composition of an artisanal crystallizer pond and functional insights into salt-saturated hypersaline environment adaptation(2018) Plominsky, Alvaro M.; Henríquez Castillo, Carlos Andrés; Delherbe, Nathalie; Podell, Sheila; Ramirez Flandes, Salvador; Ugalde, Juan A.; Santibañez, Juan F.|Van den Engh, Ger; Hanselmann, Kurt; De la Iglesia Cabezas, Rodrigo Alonso; Ulloa, Osvaldo; Allen, Eric E.; Trefault Carrillo, Nicole Natalie
- ItemDiversity of the marine picocyanobacteria Prochlorococcus and Synechococcus assessed by terminal restriction fragment length polymorphisms of 16S-23S rRNA internal transcribed spacer sequences(2008) Lavin, Paris; Gomez, Patricia; Gonzalez, Bernardo; Ulloa, OsvaldoIn order to assess the appropriateness of the use of internal transcribed spacer (ITS) sequences for the study of population genetics of marine cyanobacteria, we amplified and cloned the 16S rRNA gene plus the 16S-23S ITS regions of six strains of Prochlorococcus and Synechococcus. We analyzed them by denaturing gradient gel electrophoresis (DGGE) and terminal restriction fragment length polymorphisms (T-RFLP). When using the standard application of these techniques, We obtained more than one band or terminal restriction fragment (T-RF) per strain or cloned sequence. Reports in literature have Suggested that these anomalies can result from the formation of secondary structures. Secondary structures of the ITS sequences of Prochlorococcus and Synechococcus strains were computationally modelled at the different temperatures that were used during the polymerase chain reaction (PCR). Modelling results predicted the existence of hairpin loops that would still be present at the extension temperature; it is likely that these loops produced incomplete and single stranded PCR products. We modified the standard T-RFLP procedure by adding the labelled ITS primer in the last two cycles of the PCR reaction: this resulted, in most cases, in only one T-RF per ribotype. Application of this technique to a natural picoplankton community in marine waters off northern Chile, showed that it was possible to identify the presence, and determine the relative abundance, of several phylogenetic lineages within the genera Prochlorococcus and Synechococcus inhabiting the euphotic zone. Phylogenetic analysis of ITS sequences obtained by cloning and sequencing DNA from the same sample confirmed the presence of the different genotypes. With the proposed modification, T-RFLP profiles should therefore be Suitable for studying the diversity of natural populations of cyanobacteria, and should become an important tool to study the factors influencing the genetic Structure and distribution of these organisms.
- ItemDo phytoplankton require oxygen to survive? A hypothesis and model synthesis from oxygen minimum zones(2023) Wong, Jane C. Y.; Raven, John A.; Aldunate, Montserrat; Silva, Sebastian; Gaitan-Espitia, Juan Diego; Vargas, Cristian A.; Ulloa, Osvaldo; von Dassow, PeterIt is commonly known that phytoplankton have a pivotal role in marine biogeochemistry and ecosystems as carbon fixers and oxygen producers, but their response to deoxygenation has scarcely been studied. Nonetheless, in the major oceanic oxygen minimum zones (OMZs), all surface phytoplankton groups, regardless of size, disappear and are replaced by unique cyanobacteria lineages below the oxycline. To develop reasonable hypotheses to explain this pattern, we conduct a review of available information on OMZ phytoplankton, and we re-analyze previously published data (flow cytometric and hydrographic) on vertical structure of phytoplankton communities in relation to light and O-2 levels. We also review the physical constraints on O-2 acquisition as well as O-2-dependent metabolisms in phototrophs. These considerations, along with estimates of the photosynthetic capacity of phytoplankton along OMZ depth profiles using published data, suggest that top-down grazing, respiratory demand, and irradiance are insufficient to fully explain the vertical structure observed in the upper, more sunlit portions of OMZs. Photorespiration and water-water cycles are O-2-dependent pathways with low O-2 affinities. Although their metabolic roles are still poorly understood, a hypothetical dependence on such pathways by the phytoplankton adapted to the oxic ocean might explain vertical patterns in OMZs and results of laboratory experiments. This can be represented in a simple model in which the requirement for photorespiration in surface phytoplankton and O-2-inhibition of OMZ lineages reproduces the observed vertical fluorescence profiles and the replacement of phytoplankton adapted to O-2 by lineages restricted to the most O-2-deficient waters. A high O-2 requirement by modern phytoplankton would suggest a positive feedback that intensifies trends in OMZ extent and ocean oxygenation or deoxygenation, both in Earth's past and in response to current climate change.
- ItemMetabolic potential and in situ transcriptomic profiles of previously uncharacterized key microbial groups involved in coupled carbon, nitrogen and sulfur cycling in anoxic marine zones(2018) Plominsky, Alvaro M.; Trefault Carrillo, Nicole Natalie; Podell, Sheila; Blanton, Jessica M.; De la Iglesia Cabezas, Rodrigo Alonso; Allen, Eric E.; Dassow, Peter von; Ulloa, Osvaldo
- ItemNovel lineages of Prochlorococcus thrive within the oxygen minimum zone of the eastern tropical South Pacific(2010) Lavin, Paris; Gonzalez, Bernardo; Francisco Santibanez, J.; Scanlan, David J.; Ulloa, OsvaldoP>The eastern tropical Pacific Ocean holds two of the main oceanic oxygen minimum zones of the global ocean. The presence of an oxygen-depleted layer at intermediate depths, which also impinges on the seafloor and in some cases the euphotic zone, plays a significant role in structuring both pelagic and benthic communities, and also in the vertical partitioning of microbial assemblages. Here, we assessed the genetic diversity and distribution of natural populations of the cyanobacteria Prochlorococcus and Synechococcus within oxic and suboxic waters of the eastern tropical Pacific using cloning and sequencing, and terminal restriction fragment length polymorphism (T-RFLP) analyses applied to the 16S-23S rRNA internal transcribed spacer region. With the T-RFLP approach we could discriminate 19 cyanobacterial clades, of which 18 were present in the study region. Synechococcus was more abundant in the surface oxic waters of the eastern South Pacific, while Prochlorococcus dominated the subsurface low-oxygen waters. Two of the dominant clades in the oxygen-deficient waters belong to novel and yet uncultivated lineages of low-light adapted Prochlorococcus.
- ItemThe Influence of pCO2-Driven Ocean Acidification on Open Ocean Bacterial Communities during A Short-Term Microcosm Experiment in the Eastern Tropical South Pacific (ETSP) off Northern Chile(2020) Aguayo, Paulina; Campos, Victor L.; Henriquez, Carlos; Olivares, Francisca; Iglesia, Rodrigo De Ia; Ulloa, Osvaldo; Vargas, Cristian A.Due to the increasing anthropogenic CO2 emissions, Ocean Acidification (OA) is progressing rapidly around the world. Despite the major role that microorganisms play on the marine biogeochemical cycling and ecosystem functioning, the response of bacterial communities upon OA scenarios is still not well understood. Here, we have conducted a detailed characterization of the composition and relative abundance of bacterial communities in the water column of an open-ocean station in the Eastern Tropical South Pacific (ETSP) off northern Chile and their interactions with environmental factors. In addition, through a short-term microcosm experiment, we have assessed the effect of low pH/high pCO(2) conditions over the abundance and genetic diversity of bacterial communities. Our results evidence a clear partitioning of community composition that could be attributed mostly to dissolved oxygen. However, our experimental approach demonstrated that low pH/high pCO(2) conditions might modify the structure of the bacterial community, evidencing that small changes in pH may impact significantly the abundance and diversity of key microorganisms. This study constitutes a first step aiming to provide insight about the influence of changing carbonate chemistry conditions on natural bacterial communities and to shed light on the potential impact of OA in biogeochemical cycles on the ETSP region.