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Response of marine bacterioplankton pH homeostasis gene expression to elevated CO2
Linnaeus University, Faculty of Health and Life Sciences, Department of Biology and Environmental Science. (Centre for Ecology and Evolution in Microbial Model Systems, EEMiS)
Linnaeus University, Faculty of Health and Life Sciences, Department of Biology and Environmental Science. (Centre for Ecology and Evolution in Microbial Model Systems, EEMiS)ORCID iD: 0000-0002-8779-6464
Linnaeus University, Faculty of Health and Life Sciences, Department of Biology and Environmental Science. (Centre for Ecology and Evolution in Microbial Model Systems, EEMiS)
Linnaeus University, Faculty of Health and Life Sciences, Department of Biology and Environmental Science. (Centre for Ecology and Evolution in Microbial Model Systems, EEMiS)
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2016 (English)In: Nature Climate Change, ISSN 1758-678X, E-ISSN 1758-6798, Vol. 6, no 5, p. 483-487Article in journal (Refereed) Published
Abstract [en]

Human-induced ocean acidification impacts marine life. Marine bacteria are major drivers of biogeochemical nutrient cycles and energy fluxes1; hence, understanding their performance under projected climate change scenarios is crucial for assessing ecosystem functioning. Whereas genetic and physiological responses of phytoplankton to ocean acidification are being disentangled2, 3, 4, corresponding functional responses of bacterioplankton to pH reduction from elevated CO2 are essentially unknown. Here we show, from metatranscriptome analyses of a phytoplankton bloom mesocosm experiment, that marine bacteria responded to lowered pH by enhancing the expression of genes encoding proton pumps, such as respiration complexes, proteorhodopsin and membrane transporters. Moreover, taxonomic transcript analysis showed that distinct bacterial groups expressed different pH homeostasis genes in response to elevated CO2. These responses were substantial for numerous pH homeostasis genes under low-chlorophyll conditions (chlorophyll a <2.5 μg l−1); however, the changes in gene expression under high-chlorophyll conditions (chlorophyll a >20 μg l−1) were low. Given that proton expulsion through pH homeostasis mechanisms is energetically costly, these findings suggest that bacterioplankton adaptation to ocean acidification could have long-term effects on the economy of ocean ecosystems.

Place, publisher, year, edition, pages
2016. Vol. 6, no 5, p. 483-487
National Category
Microbiology Ecology Climate Research
Research subject
Ecology, Microbiology
Identifiers
URN: urn:nbn:se:lnu:diva-49969DOI: 10.1038/nclimate2914ISI: 000375125200015Scopus ID: 2-s2.0-84964949342OAI: oai:DiVA.org:lnu-49969DiVA, id: diva2:907477
Projects
EcoChangeAvailable from: 2016-02-29 Created: 2016-02-29 Last updated: 2018-04-24Bibliographically approved
In thesis
1. Bacterioplankton in the light of seasonality and environmental drivers
Open this publication in new window or tab >>Bacterioplankton in the light of seasonality and environmental drivers
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Bacterioplankton are keystone organisms in marine ecosystems. They are important for element cycles, by transforming dissolved organic carbon and other nutrients. Bacterioplankton community composition and productivity rates change in surface waters over spatial and temporal scales. Yet, many underlying biological processes determining when, why and how bacterioplankton react to changes in environmental conditions are poorly understood. Here, I used experiments with model bacteria and natural assemblages as well as field studies to determine molecular, physiological and ecological responses allowing marine bacteria to adapt to their environment.

Experiments with the flavobacterium Dokdonia sp. MED134 aimed to determine how the metabolism of bacteria is influenced by light and different organic matter. Under light exposure, Dokdonia sp. MED134 expressed proteorhodopsin and adjusted its metabolism to use resources more efficiently when growing with lower-quality organic matter. Similar expression patterns were found in oceanic datasets, implying a global importance of photoheterotrophic metabolisms for the ecology of bacterioplankton.

Further, I investigated how the composition and physiology of bacterial assemblages are affected by elevated CO2 concentrations and inorganic nutrients. In a large-scale experiment, bacterioplankton could keep productivity and community structure unaltered by adapting the gene expression under CO2 stress. To maintain pH homeostasis, bacteria induced higher expression of genes related to respiration, membrane transport and light acquisition under low-nutrient conditions. Under high-nutrient conditions with phytoplankton blooms, such regulatory mechanisms were not necessary. These findings indicate that open ocean systems are more vulnerable to ocean acidification than coastal waters.

Lastly, I used field studies to resolve how bacterioplankton is influenced by environmental changes, and how this leads to seasonal succession of marine bacteria. Using high frequency sampling over three years, we uncovered notable variability both between and within years in several biological features that rapidly changed over short time scales. These included potential phytoplankton-bacteria linkages, substrate uptake rates, and shifts in bacterial community structure. Thus, high resolution time series can provide important insights into the mechanisms controlling microbial communities.

Overall, this thesis highlights the advantages of combining molecular and traditional oceanographic methodological approaches to study ecosystems at high resolution for improving our understanding of the physiology and ecology of microbial communities and, ultimately, how they influence biogeochemical processes.

Place, publisher, year, edition, pages
Växjö: Linnaeus University Press, 2017. p. 62
Series
Linnaeus University Dissertations ; 303/2017
Keywords
marine bacteria, marine microbiology, seasonal succession, ocean acidification, proteorhodopsin, photoheterotrophy, microbial time series
National Category
Environmental Sciences Oceanography, Hydrology and Water Resources Microbiology
Research subject
Ecology, Aquatic Ecology; Ecology, Microbiology; Natural Science, Environmental Science
Identifiers
urn:nbn:se:lnu:diva-69130 (URN)978-91-88761-03-3 (ISBN)978-91-88761-02-6 (ISBN)
Public defence
2018-01-12, Fullriggaren, Sjöfartshögskolan, Kalmar, 09:30 (English)
Supervisors
Funder
Ecosystem dynamics in the Baltic Sea in a changing climate perspective - ECOCHANGESwedish Research Council
Available from: 2017-12-11 Created: 2017-12-11 Last updated: 2018-02-21Bibliographically approved

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Bunse, CarinaLundin, DanielKarlsson, Christofer M. G.Akram, NeelamPalovaara, JoakimSvensson, LovisaHolmfeldt, KarinDopson, MarkPinhassi, Jarone

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Bunse, CarinaLundin, DanielKarlsson, Christofer M. G.Akram, NeelamPalovaara, JoakimSvensson, LovisaHolmfeldt, KarinDopson, MarkPinhassi, Jarone
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