1. |
- Aguilera, Anabella, et al.
(author)
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Ecophysiological analysis reveals distinct environmental preferences in closely related Baltic Sea picocyanobacteria
- 2023
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In: Environmental Microbiology. - Chichester : John Wiley & Sons. - 1462-2912 .- 1462-2920. ; 25:9, s. 1674-1695
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Journal article (peer-reviewed)abstract
- Cluster 5 picocyanobacteria significantly contribute to primary productivity in aquatic ecosystems. Estuarine populations are highly diverse and consist of many co-occurring strains, but their physiology remains largely understudied. In this study, we characterized 17 novel estuarine picocyanobacterial strains. Phylogenetic analysis of the 16S rRNA and pigment genes (cpcBandcpeBA) uncovered multiple estuarine and freshwater-related clusters and pigment types. Assays with five representative strains (three phycocyanin rich and two phycoerythrin rich) under temperature (10–30°C), light(10–190 μmol photons m-2s-1), and salinity (2–14 PSU) gradients revealed distinct growth optima and tolerance, indicating that genetic variability was accompanied by physiological diversity. Adaptability to environmental conditions was associated with differential pigment content and photosynthetic performance. Amplicon sequence variants at a coastal and an offshore station linked population dynamics with phylogenetic clusters, supporting that strains isolated in this study represent key ecotypes within the Baltic Sea picocyanobacterial community. The functional diversity found within strains with the same pigment type suggests that understanding estuarine picocyanobacterial ecology requires analysis beyond the phycocyanin and phycoerythrin divide. This new knowledge of the environmental preferences in estuarine picocyanobacteria is important for understanding and evaluating productivity in current and future ecosystems.
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2. |
- Alegria Zufia, Javier, Ph.D. 1992-, et al.
(author)
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Growth and mortality rates of picophytoplankton in the Baltic Sea Proper
- 2024
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In: Marine Ecology Progress Series. - Oldendorf : Inter-Research. - 0171-8630 .- 1616-1599. ; 735, s. 63-76
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Journal article (peer-reviewed)abstract
- Picophytoplankton (<2 µm diameter), a diverse group of picocyanobacteria and photosynthetic picoeukaryotes, are significant contributors to primary production. Predatory mortality controls picophytoplankton biomass and thereby energy transfer in the marine food web. The 2 major pathways of picophytoplankton mortality are grazing and viral lysis. Grazing passes carbon directly to higher trophic levels, while lysis products are passed into the viral loop. Picophytoplankton are abundant in the Baltic Sea but little is known about their predatory mortality. Using a modification of the dilution approach, we calculated growth and mortality rates of picophytoplankton and studied the effect of predation on community structure during late August and September. The experiments were conducted coinciding with the peak in picophytoplankton abundance (similar to 10(5) cells ml(-1)) at the Linnaeus Microbial Observatory in the Baltic Sea Proper. The results showed that grazing is an important controller of picocyanobacteria and photosynthetic picoeukaryote populations, while no significant viral lysis effect was detected. Grazing on picocyanobacteria was proportional to growth rates, while grazing on photosynthetic picoeukaryotes exceeded growth. Selective grazing of phylogenetically distinct picocyanobacterial clades had a significant effect on community structure, suggesting that grazing has an impact on the seasonal dynamics of co-occurring clades. Picocyanobacteria had a higher carbon transfer contribution to higher trophic levels than photosynthetic picoeukaryotes at the time of the experiments. The study shows that picophytoplankton are important contributors to carbon cycling in the Baltic Sea microbial food web and should be considered for future ecological models.
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3. |
- Alegria Zufía, Javier, Ph.D. 1992-
(author)
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Picophytoplankton seasonal dynamics in the Baltic Sea
- 2022
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Doctoral thesis (other academic/artistic)abstract
- Picophytoplankton (<2 μm diameter) is a diverse group of picocyanobacterial and photosynthetic picoeukaryotes (PPE).Picophytoplankton contribute significantly to total phytoplankton biomassand can dominate primary production in oceans, lakes and estuaries. In the estuarine Baltic Sea, the composition of picophytoplankton is linked to the north to south salinity gradient but knowledge of the seasonal dynamics interms of abundance, biomass and diversity is largely unknown. This thesis investigated the in situ dynamics, bottom up and top down controls of picocyanobacteria (SYN; consisting of primarily Synechococcus and Cyanobium among other genuses) and PPE at two sampling stations, one coastal and one offshore. Monitoring data over three years (2018-2020) showed high biomass contribution across all seasons. Picocyanobacterial peak abundances occurred from spring to summer at the coastal station and in late-summer to autumn at the offshore station (up to 4.7 × 105 cells mL-1).Differentiation of pigment populations showed that phycoerythrin rich(PE)-SYN was the main contributor to SYN abundances except at the coastalstation during summer, when PE-SYN and phycocyanin rich (PC)-SYN had equal contributions. PPE peak abundances occurred during late summer to autumn (up to 1.1 × 105 cells mL-1 cells ml-1). Temperature was linked topicophytoplankton growth and abundance, with PE-SYN, PCSYN and PPEadapted to different temperature ranges. Temperature also affected SYNnitrogen preference: SYN was nitrogen limited during early summer and at>15°C there was a preference for ammonium over nitrate. Clade A/B dominated the SYN community, except during summer at the coastal station when low nitrate and warm temperatures promoted S5.2 dominance. Grazing was observed to control SYN and PPE abundances and had an effect on the SYN community structure. Identification and laboratory experiments of key Synechococcus strains using a range of salinity, temperature and light conditions provided important insights into the physiological diversity of co-occurring ecotypes and links to the SYN dynamics that were observed in the field. In summary, this thesis provided novel information of picophytoplankton dynamics and community structure in the Baltic Sea. The results show that picophytoplankton play a relevant role in Baltic Sea and shows the importance of monitoring programs to understand picophytoplankton dynamics.
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4. |
- Alegria Zufia, Javier, Ph.D. 1992-, et al.
(author)
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Seasonal dynamics in picocyanobacterial abundance and clade composition at coastal and offshore stations in the Baltic Sea
- 2022
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In: Scientific Reports. - London : Nature Publishing Group. - 2045-2322. ; 12:1
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Journal article (peer-reviewed)abstract
- Picocyanobacteria (< 2 um in diameter) are significant contributors to total phytoplankton biomass. Due to the high diversity within this group, their seasonal dynamics and relationship with environmental parameters, especially in brackish waters, are largely unknown. In this study, the abundance and community composition of phycoerythrin rich picocyanobacteria (PE-SYN) and phycocyanin rich picocyanobacteria (PC-SYN) were monitored at a coastal (K-station) and at an offshore station (LMO; similar to 10 km from land) in the Baltic Sea over three years (2018-2020). Cell abundances of picocyanobacteria correlated positively to temperature and negatively to nitrate (NO3) concentration. While PE-SYN abundance correlated to the presence of nitrogen fixers, PC-SYN abundance was linked to stratification/shallow waters. The picocyanobacterial targeted amplicon sequencing revealed an unprecedented diversity of 2169 picocyanobacterial amplicons sequence variants (ASVs). A unique assemblage of distinct picocyanobacterial clades across seasons was identified. Clade A/B dominated the picocyanobacterial community, except during summer when low NO3, high phosphate (PO4) concentrations and warm temperatures promoted S5.2 dominance. This study, providing multiyear data, links picocyanobacterial populations to environmental parameters. The difference in the response of the two functional groups and clades underscore the need for further high-resolution studies to understand their role in the ecosystem.
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5. |
- Alegria Zufia, Javier, et al.
(author)
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Seasonality of Coastal Picophytoplankton Growth, Nutrient Limitation, and Biomass Contribution
- 2021
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In: Frontiers in Microbiology. - Lausanne : Frontiers Media S.A.. - 1664-302X. ; 12
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Journal article (peer-reviewed)abstract
- Picophytoplankton in the Baltic Sea includes the simplest unicellular cyanoprokaryotes (Synechococcus/Cyanobium) and photosynthetic picoeukaryotes (PPE). Picophytoplankton are thought to be a key component of the phytoplankton community, but their seasonal dynamics and relationships with nutrients and temperature are largely unknown. We monitored pico- and larger phytoplankton at a coastal site in Kalmar Sound (K-Station) weekly during 2018. Among the cyanoprokaryotes, phycoerythrin-rich picocyanobacteria (PE-rich) dominated in spring and summer while phycocyanin-rich picocyanobacteria (PC-rich) dominated during autumn. PE-rich and PC-rich abundances peaked during summer (1.1 x 10(5) and 2.0 x 10(5) cells mL(-1)) while PPE reached highest abundances in spring (1.1 x 10(5) cells mL(-1)). PPE was the main contributor to the total phytoplankton biomass (up to 73%). To assess nutrient limitation, bioassays with combinations of nitrogen (NO3 or NH4) and phosphorus additions were performed. PE-rich and PC-rich growth was mainly limited by nitrogen, with a preference for NH4 at >15 degrees C. The three groups had distinct seasonal dynamics and different temperature ranges: 10 degrees C and 17-19 degrees C for PE-rich, 13-16 degrees C for PC-rich and 11-15 degrees C for PPE. We conclude that picophytoplankton contribute significantly to the carbon cycle in the coastal Baltic Sea and underscore the importance of investigating populations to assess the consequences of the combination of high temperature and NH4 in a future climate.
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6. |
- Laber, Christien P., et al.
(author)
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Colony-forming and single-cell picocyanobacteria nitrogen acquisition strategies and carbon fixation in the brackish Baltic Sea
- 2024
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In: Limnology and Oceanography. - Hoboken, NJ : John Wiley & Sons. - 0024-3590 .- 1939-5590.
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Journal article (peer-reviewed)abstract
- Picocyanobacteria are widespread and globally significant primary producers. In brackish waters, picocyanobacterial populations are composed of diverse species with both single-cell and colony-forming lifestyles. Compared to their marine counterparts, brackish picocyanobacteria are less well characterized and the focus of research has been weighted toward single-cell picocyanobacteria. Here, we investigate the uptake dynamics of single and colony-forming picocyanobacteria using incubations with dual carbon-13 and inorganic (ammonium and nitrate) or organic (urea and amino acids) nitrogen-15 sources during August and September 2020 in the central Baltic Sea. Phytoplankton community and group-specific uptake rates were obtained using an elemental analyzer isotope ratio mass spectrometer (EA-IRMS) and nano secondary-ion mass spectrometry (NanoSIMS). Picocyanobacteria contributed greater than one third of the ammonium, urea, amino acids, and inorganic carbon community uptake/fixation in September but < 10% in August when phytoplankton biomass was higher. Overall, single-cell ammonium and urea uptake rates were significantly higher for single-celled compared to colonial picocyanobacteria. In a 6-yr offshore central Baltic Sea time series (2015-2020), summer abundances of colonial picocyanobacteria reached up to 10(5) cells mL(-1) and represented > 5% of the average phytoplankton biomass, suggesting that they are periodically important for the ecosystem. Colonial strain identification was not distinguishable using 16S rRNA gene amplicon data, highlighting a need for refined tools for identification of colonial forms. This study shows the significance of single-celled brackish picocyanobacteria to nutrient cycling and the importance of considering uptake and lifestyle strategies when assessing the role of picocyanobacteria in aquatic ecosystems.
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