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Selective degradation of different dissolved organic matter compounds by regionally transplanted bacteria.
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
(Center for Microbial Oceanography Research and Education., University of Hawaií at Mānoa, Honolulu. USA.)
(Civil and Environmental Engineering, Water Environment Technology, Chalmers University of Technology, Gothenburg. Sweden.)
(Department of Aquatic Ecology, Lund University. Sweden.)
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

Climate change projections indicate that precipitation will increase by ~30% in the Baltic Sea within the next hundred years. This will lead to lowered salinity and increased inputs of dissolved organic matter (DOM) to the sea. The interactive effects of these changes on bacterial communities and DOM degradation are virtually unknown. We studied the selective degradation of different DOM compounds by regionally transplanted bacterial communities. Bacteria from the northern Baltic Sea were transplanted and re-transplanted to the southern Baltic Sea and vice versa. Three fractions of DOM were identified; two allochthonous fractions, originating from terrestrial systems and one autochthononous constituting the protein building blocks tryptophan/tyrosine. The largest decrease of dissolved organic carbon was observed in seawater from the Bothnian Sea (northern Baltic Sea), and the bacteria performing this degradation were those transplanted from the Baltic Proper (southern Baltic Sea). The native bacteria from the Bothnian Sea degraded both allochthonous and autochthonous DOM, while, bacteria from the Baltic Proper consumed mainly the autochthonous part of the DOM. Both autochthonous and allochthonous components of the DOM were found to shape the bacterioplankton community, Cyanobacteria and γ-proteobacteria were favored by all three DOM components, while α-proteobacteria and Bacteroidetes were favored by autochthonous DOM and β-proteobacteria by terrestrial DOM. However, no clear connection between different DOM components, specific bacterial groups and metabolic processes could be identified. Our study thus indicates that climate change can cause unforeseen adjustments of the bacterial community composition and function, governed by complex interactions between bacteria and their chemical environment.

Keyword [en]
Dissolved organic matter composition; selective degradation; regionally transplanted bacteria, bacterioplankton community changes; Baltic Sea.
National Category
Ecology
Research subject
Earth Sciences with Specialization Environmental Analysis
Identifiers
URN: urn:nbn:se:umu:diva-117974OAI: oai:DiVA.org:umu-117974DiVA: diva2:910193
Funder
Ecosystem dynamics in the Baltic Sea in a changing climate perspective - ECOCHANGE
Available from: 2016-03-08 Created: 2016-03-08 Last updated: 2016-03-10
In thesis
1. Bacterioplankton in the Baltic Sea: influence of allochthonous organic matter and salinity
Open this publication in new window or tab >>Bacterioplankton in the Baltic Sea: influence of allochthonous organic matter and salinity
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Climate change is expected to increase the precipitation ~30% in higher latitudes during the next century, increasing the land runoff via rivers to aquatic ecosystems. The Baltic Sea will receive higher river discharges, accompanied by larger input of allochthonous dissolved organic matter (DOM) from terrestrial ecosystems. The salinity will decrease due to freshwater dilution. The allochthonous DOM constitute a potential growth substrate for microscopic bacterioplankton and phytoplankton, which together make up the basal trophic level in the sea. The aim of my thesis is to elucidate the bacterial processing of allochthonous DOM and to evaluate possible consequences of increased runoff on the basal level of the food web in the Baltic Sea. I performed field studies, microcosm experiments and a theoretical modeling study.

Results from the field studies showed that allochthonous DOM input via river load promotes the heterotrophic bacterial production and influences the bacterial community composition in the northern Baltic Sea. In a northerly estuary ~60% of bacterial production was estimated to be sustained by terrestrial sources, and allochthonous DOM was a strong structuring factor for the bacterial community composition. Network analysis showed that during spring the diversity and the interactions between the bacteria were relatively low, while later during summer other environmental factors regulate the community, allowing a higher diversity and more interactions between different bacterial groups. The influence of the river inflow on the bacterial community allowed “generalists” bacteria to be more abundant than “specialists” bacteria.   

Results from a transplantation experiment, where bacteria were transplanted from the northern Baltic Sea to the seawater from the southern Baltic Sea and vice versa, showed that salinity, as well as the DOM composition affect the bacterial community composition and their enzymatic activity. The results showed that α-proteobacteria in general were favoured by high salinity, β-proteobacteria by low salinity and terrestrial DOM compounds and γ-proteobacteria by the enclosure itself. However, effects on the community composition and enzymatic activity were not consistent when the bacterial community was retransplanted, indicating a functional redundancy of the bacterial communities. 

Results of ecosystem modeling showed that climate change is likely to have quite different effect on the north and the south of the Baltic Sea. In the south, higher temperature and internal nutrient load will increase the cyanobacterial blooms and expand the anoxic or suboxic areas. In the north, climate induced increase in riverine inputs of allochthonous DOM is likely to promote bacterioplankton production, while phytoplankton primary production will be hampered due to increased light attenuation in the water. This, in turn, can decrease the production at higher trophic levels, since bacteria-based food webs in general are less efficient than food webs based on phytoplankton. However, complex environmental influences on the bacterial community structure and the large redundancy of metabolic functions limit the possibility of predicting how the bacterial community composition will change under climate change disturbances.

Place, publisher, year, edition, pages
Umeå: Umeå Universitet, 2016. 23 p.
Keyword
Bacterioplankton production; bacterial community structure; allochthonous organic matter; carbon utilization; dissolved organic carbon composition; bacterioplankton ecological function; bacterial diversity; bacterial network; Baltic Sea estuary; food web; climate change.
National Category
Ecology
Research subject
biology, Environmental Science
Identifiers
urn:nbn:se:umu:diva-117977 (URN)978-91-7601-412-7 (ISBN)
Public defence
2016-04-01, KB3B1, Linnaeus väg 6 (Chemical Biological Center, KBC), Umeå, 10:00 (English)
Opponent
Supervisors
Funder
Ecosystem dynamics in the Baltic Sea in a changing climate perspective - ECOCHANGE
Available from: 2016-03-11 Created: 2016-03-08 Last updated: 2016-03-10Bibliographically approved

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Figueroa, DanielaAndersson, Agneta
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