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Diatoms dominate the eukaryotic metatranscriptome during spring in coastal 'dead zone' sediments
Linnaeus University, Faculty of Health and Life Sciences, Department of Biology and Environmental Science. (Ctr Ecol & Evolut Microbial Model Syst EEMiS)ORCID iD: 0000-0001-9005-5168
Linnaeus University, Faculty of Health and Life Sciences, Department of Biology and Environmental Science. (Ctr Ecol & Evolut Microbial Model Syst EEMiS)
Linnaeus University, Faculty of Health and Life Sciences, Department of Biology and Environmental Science.ORCID iD: 0000-0002-9622-3318
Linnaeus University, Faculty of Health and Life Sciences, Department of Biology and Environmental Science. (Ctr Ecol & Evolut Microbial Model Syst EEMiS ; Zooplankton ecology)ORCID iD: 0000-0002-3740-5998
2017 (English)In: Proceedings of the Royal Society of London. Biological Sciences, ISSN 0962-8452, E-ISSN 1471-2954, Vol. 284, no 1864, article id 20171617Article in journal (Refereed) Published
Abstract [en]

An important characteristic of marine sediments is the oxygen concentration that affects many central metabolic processes. There has been a widespread increase in hypoxia in coastal systems (referred to as 'dead zones') mainly caused by eutrophication. Hence, it is central to understand the metabolism and ecology of eukaryotic life in sediments during changing oxygen conditions. Therefore, we sampled coastal 'dead zone' Baltic Sea sediment during autumn and spring, and analysed the eukaryotic metatranscriptome from field samples and after incubation in the dark under oxic or anoxic conditions. Bacillariophyta (diatoms) dominated the eukaryotic metatranscriptome in spring and were also abundant during autumn. A large fraction of the diatom RNA reads was associated with the photosystems suggesting a constitutive expression in darkness. Microscope observation showed intact diatom cells and these would, if hatched, represent a significant part of the pelagic phytoplankton biomass. Oxygenation did not significantly change the relative proportion of diatoms nor resulted in any major shifts in metabolic 'signatures'. By contrast, diatoms rapidly responded when exposed to light suggesting that light is limiting diatom development in hypoxic sediments. Hence, it is suggested that diatoms in hypoxic sediments are on 'standby' to exploit the environment if they reach suitable habitats.

Place, publisher, year, edition, pages
2017. Vol. 284, no 1864, article id 20171617
Keyword [en]
diatoms, sediment, oxygen, anoxia, metatranscriptomics
National Category
Ecology
Research subject
Ecology, Aquatic Ecology
Identifiers
URN: urn:nbn:se:lnu:diva-68552DOI: 10.1098/rspb.2017.1617ISI: 000412553400005OAI: oai:DiVA.org:lnu-68552DiVA, id: diva2:1154199
Projects
EcoChange
Funder
Ecosystem dynamics in the Baltic Sea in a changing climate perspective - ECOCHANGE
Available from: 2017-11-01 Created: 2017-11-01 Last updated: 2018-04-24Bibliographically approved
In thesis
1. Ecology and evolution of coastal Baltic Sea 'dead zone' sediments
Open this publication in new window or tab >>Ecology and evolution of coastal Baltic Sea 'dead zone' sediments
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Since industrialization and the release of agricultural fertilizers began, coastal and open waters of the Baltic Sea have been loaded with nutrients. This has increased the growth of algal blooms and because a portion of the algal organic matter sinks to the sea floor, hypoxia has increased. In conjunction to this, natural stratification of the water column makes the bottom zones especially prone to oxygen depletion due to microbes using oxygen and organic matter to grow. Hypoxia (<2 mg/L O2) and anoxia (no oxygen) are deadly for many organisms and only specialists (typically some microorganisms) are able to survive. Due to the harsh conditions these bottom zones are commonly referred to as 'dead zones'. The focus of this thesis was to look closer at the microbial community changes upon degradation of algal organic matter and the effect of oxygenating coastal Baltic Sea 'dead zone' sediments on chemistry fluxes, phyto- and zooplankton, the microbial community structure, and microbial metabolic responses. Results from field sampling and incubation experiments showed that degradation of algal biomass in nutrient rich oxic sediment was partly related to the growth of archaea; that oxygenation of anoxic sediments decreased stored organic matter plus triggered hatching of zooplankton eggs increasing the benthic-pelagic coupling; and resting diatoms buried in hypoxic/anoxic sediment were alive and triggered to germinate by light rather than oxygen. Changes in the microbial community structures to oxygen shifts were dependent on the historical exposure to oxygen and that microbial generalists adapted to episodic oxygenation were favored during oxygen shifts. Facultative anaerobic sulfur/sulfide oxidizing bacterial genera were favored upon oxygenation of hypoxic/anoxic sediment plus sulfur cycling and nitrogen fixation genes were abundant. Finally, it was discovered that oxygenation regulates metabolic processes involved in the sulfur and methane cycles, especially by metabolic processes that results in a decrease of toxic hydrogen sulfide as well as the potent greenhouse gas methane. This thesis has explored how 'dead zones' change and develop during oxygen shifts and that re-oxygenation of ‘dead zones’ could bring favorable conditions in the sediment surface for reestablishment of new micro- and macroorganism communities.

Abstract [sv]

Arealerna av 'döda bottnar' i Östersjön har ökat som en följd av industrialiseringen och användandet av gödningsmedel. Föroreningen av Östersjöns kust och öppna vatten med näringsämnen leder till en ökad tillväxt av algblomningar. En del av dessa alger sjunker till havsbotten och orsakar att så kallad hypoxia utvecklas. Den naturliga stratifieringen av vattenkolummen avgränsar yt- och bottenvattnet vilket leder till att bottenzonen är speciellt utsatt för syrebrist. Detta eftersom mikroorganismer i bottensedimentet använder syre och organiskt material för att leva. Hypoxia (<2 mg/L O2) och anoxia (inget syre) är dödligt för de flesta organismer och endast specialiserade organismer (vanligtvis vissa mikroorganismer) kan överleva. Det är av denna anledning dessa bottenzoner ofta kallas för 'döda bottnar'. Målet med denna avhandling var att undersöka förändringar i de mikrobiologiska samhällena vid nedbrytning av organiskt algmaterial, och undersöka vilken effekt syresättning har på ekologin i döda bottensediment i Östersjöns kust. I mer detalj studerades kemiska flöden, växt- och djurplankton, samt mikrobiologiska samhällen och deras metaboliska processer. Resultaten från fältprovtagningar och inkubationer i laboratoriet visade att nedbrytning av algmaterial i syrerikt sediment till viss del gynnade arkéer; syretillsättning av anoxiska sediment minskade det lagrade organiska materialet och ledde till ökad kläckning av djurplanktonägg; vilande kiselalger begravda i hypoxisk/anoxisk sediment var levande och vaknade vid tillförsel av ljus snarare än syre. Förändringar i mikrobiologiska samhällen vid syreförändringar var beroende av historisk exponering av syre i sedimentytan. Det observerades också att mikroorganismer anpassade till episodiska förändringar i syre gynnades. Fakultativt anaerobiska svavel/sulfidoxiderande bakteriesläkten gynnades efter syresättning av hypoxisk/anoxiskt sediment och gener involverade i omvandling av svavelämnen och kvävefixering var vanliga. Slutligen visade resultaten att syresättning reglerar metaboliska processer involverade i kretsloppen för svavel och metan. Speciellt genom processer som leder till en minskning av den gifta gasen svavelväte och växthusgasen metan. Denna avhandling har undersökt hur döda bottensediment förändras och utvecklas vid skiftande syreförhållanden och visar att syresättning av 'döda bottnar' kan skapa gynnsamma förhållanden i sedimentytan för återetablering av mikro- och makroorganismsamhällen. 

Place, publisher, year, edition, pages
Växjö: Linnaeus University Press, 2018
Series
Linnaeus University Dissertations ; 302/2018
Keyword
Baltic Sea, sediment, oxygen, metatranscriptomics, metagenomics, 16S rRNA gene, RNA-seq, dead zone, re-oxygenation
National Category
Ecology
Research subject
Ecology, Aquatic Ecology
Identifiers
urn:nbn:se:lnu:diva-69710 (URN)978-91-88761-00-2 (ISBN)978-91-88761-01-9 (ISBN)
Public defence
2018-02-02, Fullriggaren, Landgången 4, Kalmar, 13:30 (English)
Opponent
Supervisors
Available from: 2018-01-12 Created: 2018-01-11 Last updated: 2018-02-05Bibliographically approved

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Broman, EliasDopson, MarkHylander, Samuel

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