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Influence of pulsed and continuous substrate inputs on freshwater bacterial community composition and functioning in bioreactors
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.
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.
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2017 (English)Manuscript (preprint) (Other academic)
Abstract [en]

Aquatic environments are typically not homogenous, but characterized by changing substrate concentration gradients and nutrient patches. This heterogeneity in substrate availability creates a multitude of niches allowing bacteria with different substrate utilization strategies to hypothetically coexist even when competing for the same substrate. To study the impact of heterogeneous distribution of organic substrates on bacterioplankton, bioreactors with freshwater bacterial communities were fed artificial freshwater medium with acetate supplied either continuously or in pulses. After a month-long incubation, bacterial biomass and community-level substrate uptake rates were twice as high in the pulsed treatment compared to the continuously fed reactors even if the same total amount of acetate was supplied to both treatments. The composition of the bacterial communities emerging in the two treatments differed significantly with specific taxa overrepresented in the respective treatments. The higher estimated growth yield in cultures that received pulsed substrate inputs, imply that such conditions enable bacteria to use resources more efficiently for biomass production. This finding agrees with established concepts of basal maintenance energy requirements and high energetic costs to assimilate substrates at low concentration. Our results further imply that degradation of organic matter is influenced by temporal and spatial heterogeneity in substrate availability. 

Place, publisher, year, edition, pages
2017.
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:uu:diva-275178DOI: 10.1111/1462-2920.13979OAI: oai:DiVA.org:uu-275178DiVA: diva2:899142
Available from: 2016-02-01 Created: 2016-02-01 Last updated: 2017-12-04
In thesis
1. Life strategies for substrate assimilation by freshwater bacterioplankton
Open this publication in new window or tab >>Life strategies for substrate assimilation by freshwater bacterioplankton
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The availability of substrates is one of the most important environmental constraints on the diversity and functioning of microorganisms. Substrate quantity and quality as well as the metabolic features of heterotrophic microorganisms determine the efficiency, speed and type of transformation that can occur in nature. As such their interplay with the environment regulates how much carbon and energy is incorporated by bacteria and subsequently reaches higher trophic levels. In lakes the bulk substrate that is available for bacteria is composed of a complex mixture of compounds, varying in lability and distribution in the environment. This thesis addresses the coupling of organic substrates, their metabolic use and the composition and ecology of the microbial community. Controlled laboratory experiments with mixed bacterial communities in either batch cultures or chemostats were designed to shed further light on bacterial use of labile and quantitatively significant carbon compounds.

I show that different amino acid substrates only exert a minor influence on bacterioplankton community composition and growth. Hence the ability to use a wide range of such abundantly produced protein monomers seems to be widespread among freshwater bacteria. In contrast, when acetate was provided as the only carbon substrate, in either pulsed or continuous amendments, this very different substrate input mode had a strong effect on bacterial community composition. Biomass yield, for example, was twice as high when acetate was given in the form of pulses rather than provided continuously.

In another set of experiments, I show that the oxidation of the globally significant greenhouse gas methane is a process that can potentially take place at the water-ice interface of seasonally ice-covered lakes and was not constrained by temperature as suggested in previous studies. This work also suggests that methane oxidation in ice-covered lakes can be constrained by competition for nutrients between specialized methanotrophs and heterotrophic bacteria.

Combined these studies suggest that some labile substrates cause minor selection on bacterial community structure and functioning. This probably reflects the competitive advantage of using a broad range of low molecular weight substrates. However, as in the case of methanotrophs there is specialization for a specific low molecular weight substrate such as methane. In which case, competition with other community members i.e. for nutrients can constrain methane oxidation. In both cases it might however not depend just on the availability of substrate, but also on how substrates are distributed in time and space.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2016. 39 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1342
Keyword
lake, methane, bacteria, substrate, methanotrophs, pulse, chemostat
National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-275181 (URN)978-91-554-9470-4 (ISBN)
Public defence
2016-03-18, Friessalen, EBC, Norbyvägen 14, Uppsala, 09:00 (English)
Opponent
Supervisors
Available from: 2016-02-26 Created: 2016-02-01 Last updated: 2016-03-09
2. 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: 2017-11-28Bibliographically approved

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