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Effects of sterilization on composition and bacterial utilization of dissolved organic carbon
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology. ICRA, Catalan Institute of Water Research.
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology. Applied Microbiology and Biotechnology Laboratory, Department of Botany, University of Delhi.
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

Sterilization of dissolved organic carbon (DOC) is an essential step in research on interactions between DOC and organisms, for example where the effect of different microbial communities on DOC is studied or vice versa. Few studies have, however, gone beyond acknowledging that sterilization of DOC influences its characteristics. Here we aimed to provide further knowledge that enables scientists to better tailor their sterilization methods to their research question. To meet this aim, we conducted a sterilization experiment with DOC from 4 boreal lakes treated with 4 sterilization methods, 2 filtrations (0.2 µm, 0.1 µm) and 2 autoclaving approaches (single autoclaving and double with intermediate pH adjustment). Quantity and spectroscopic properties of DOC were compared before and after sterilization and DOC was further tested as a substrate for bacterial growth. We found that the filtration methods better preserved the qualities of DOC, particularly the 0.2 µm filtration. On the contrary, autoclaving caused major inconsistent shifts in both qualitative and quantitative measurements of DOC as well as an increase of the maximum abundance of bacteria in growth experiments. Nonetheless, there remains a trade-off between retaining the quality of DOC and achieving sterile conditions. Therefore, the sterilization method of choice should be guided by the scientific question at hand.    

Keyword [en]
sterilization, autoclave, filtration, dissolved organic carbon, excitation emission matrices, parallel factor analysis
National Category
Biological Sciences
Research subject
Microbiology
Identifiers
URN: urn:nbn:se:uu:diva-331676OAI: oai:DiVA.org:uu-331676DiVA: diva2:1149733
Available from: 2017-10-16 Created: 2017-10-16 Last updated: 2017-10-23
In thesis
1. Extent and limitations of functional redundancy among bacterial communities towards dissolved organic matter
Open this publication in new window or tab >>Extent and limitations of functional redundancy among bacterial communities towards dissolved organic matter
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

One of the key processes in the carbon cycle on our planet is the degradation of dissolved organic matter (DOM) in aquatic environments. The use of organic matter by bacteria links energy from DOM to higher trophic levels of the ecosystem when bacteria are consumed by other organisms. This is referred to as the microbial loop. In this thesis I examined if the communities were functionally redundant in their ability to utilize organic matter, or if variation in bacterial composition and richness is of importance. To test this overarching question several experiments were conducted that include methods such as illumina sequencing of the 16S rRNA gene for taxonomic identification of bacterial communities, flow cytometry to follow the growth of communities and spectroscopic measurement to describe the composition of the organic matter pool. Initially we demonstrated how to optimally sterilize organic matter for experimental studies in order to preserve its natural complexity. In further experiments we found that bacterial communities are redundant in their utilization of organic matter and can maintain optimal performance towards a range of organic matter pools. Related to this we found that pre-adaptation to organic matter played a small role as communities performed equally well regardless of their environmental history. We saw a small effect of richness and composition of bacterial communities on the efficiency of organic matter use, but conclude that this is of minor importance relative to abiotic factors. Still, we also show that organic matter can put strong selection pressure on bacterial communities with regards to richness and composition. Additionally we found that the supply rate of a carbon compound greatly influenced the energy utilization of the compound, i.e. a higher growth rate can be maintained if substrate is delivered in pulses relative to a continuous flow. Finally we conclude that the variation in bacterial communities is unlikely to have a major influence on carbon cycling in boreal lakes, but to enable a finer understanding, the genetics underlying the carbon utilization needs to be further explored. 

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2017. 41 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1578
Keyword
Dissolved organic matter, BCC, biodiversity, functional redundancy
National Category
Natural Sciences
Research subject
Microbiology
Identifiers
urn:nbn:se:uu:diva-331772 (URN)978-91-513-0112-9 (ISBN)
Public defence
2017-12-01, Friessalen, Norbyvägen 18, Uppsala, 09:00 (English)
Opponent
Supervisors
Available from: 2017-11-08 Created: 2017-10-17 Last updated: 2017-11-08Bibliographically approved

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