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Interactions between Bacteria and Fungi on Aquatic Detritus – Causes and Consequences
Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Faculty of Science and Technology, Biology, Department of Ecology and Evolution.
2005 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Bacteria and fungi dominate the decomposition of aquatic plants, a major process in the carbon and nutrient cycling in many aquatic systems. Although phylogenetically distant, bacteria and fungi often live in close proximity with each other. Since these microorganisms also have similar ecological functions, interactions have developed between them. This thesis explores the nature of such interactions, and the potential effects on key components of the decomposition process. The thesis includes a critical assessment of the ergosterol method for determination of fungal biomass, a survey of the environmental factors determining the distribution and taxa numbers of litter-decomposing bacteria and fungi in lakes, and a number of experiments on the interactions between bacteria and fungi. In all the experiments performed, fungi responded to bacterial presence through antagonism, although different fungal strains, bacterial communities and substrates were used. The antagonism seemed to be caused by interference competition for substrate. The fungal effect on bacteria was less consistent. Bacterial growth was suppressed, unaffected, or even enhanced by the presence of fungi. Fungi contributed more to extracellular enzyme production than bacteria, and bacteria were probably able to assimilate intermediate decomposition products formed through the activity of extracellular enzymes of fungal origin. Thus, the effect on bacteria from interacting with fungi was determined by the balance between competition and benefit from excreted enzymes. Bacteria and fungi also used different size fractions of the organic matter, according to their different enzymatic capacities. Hence, bacteria appeared to assimilate low-molecular-weight compounds, while high-molecular-weight compounds were utilized primarily by fungi.

In brief, the ecological interactions influenced the growth and hence also the biomass development of bacteria and fungi, which affected enzyme activity as well as utilization of dissolved organic matter. Therefore, I suggest that interactions between bacteria and fungi influence degradation of plant litter in aquatic systems.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis , 2005. , p. 42
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 46
Keywords [en]
Ecology, bacteria, fungi, decomposition, antagonism, extracellular enzymes, competition, macrophytes, dissolved organic carbon (DOC), ergosterol
Keywords [sv]
Ekologi
National Category
Ecology
Identifiers
URN: urn:nbn:se:uu:diva-5771ISBN: 91-554-6231-6 (print)OAI: oai:DiVA.org:uu-5771DiVA, id: diva2:166309
Public defence
2005-05-20, Ekmansalen, Kärnhuset, EBC, Norbyv. 14, Uppsala, 10:00
Opponent
Supervisors
Available from: 2005-04-29 Created: 2005-04-29Bibliographically approved
List of papers
1. Antagonism between bacteria and fungi on decomposing aquatic plant litter
Open this publication in new window or tab >>Antagonism between bacteria and fungi on decomposing aquatic plant litter
2003 In: Microbial Ecology, ISSN 0095-3628, Vol. 45, no 2, p. 173-182Article in journal (Refereed) Published
Identifiers
urn:nbn:se:uu:diva-92967 (URN)
Available from: 2005-04-29 Created: 2005-04-29 Last updated: 2017-11-30Bibliographically approved
2. Antagonism between bacteria and fungi: substrate competition and a possible trade-off between fungal growth and tolerance towards bacteria
Open this publication in new window or tab >>Antagonism between bacteria and fungi: substrate competition and a possible trade-off between fungal growth and tolerance towards bacteria
(English)Article in journal (Refereed) Submitted
Identifiers
urn:nbn:se:uu:diva-92968 (URN)
Available from: 2005-04-29 Created: 2005-04-29 Last updated: 2017-11-30Bibliographically approved
3. Interactions of bacteria and fungi on decomposing litter: Differential extracellular enzyme activities
Open this publication in new window or tab >>Interactions of bacteria and fungi on decomposing litter: Differential extracellular enzyme activities
2006 (English)In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 87, no 10, p. 2559-2569Article in journal (Refereed) Published
Abstract [en]

Fungi and bacteria are key agents in plant litter decomposition in freshwater ecosystems. However, the specific roles of these two groups and their interactions during the decomposition process are unclear. We compared the growth and patterns of degradative enzymes expressed by communities of bacteria and fungi grown separately and in coexistence on Phragmites leaves. The two groups displayed both synergistic and antagonistic interactions. Bacteria grew better together with fungi than alone. In addition, there was a negative effect of bacteria on fungi, which appeared to be caused by suppression of fungal growth and biomass accrual rather than specifically affecting enzyme activity. Fungi growing alone had a high capacity for the decomposition of plant polymers such as lignin, cellulose, and hemicellulose. In contrast, enzyme activities were in general low when bacteria grew alone, and the activity of key enzymes in the degradation of lignin and cellulose (phenol oxidase and cellobiohydrolase) was undetectable in the bacteria-only treatment. Still, biomass-specific activities of most enzymes were higher in bacteria than in fungi. The low total activity and growth of bacteria in the absence of fungi in spite of apparent high enzymatic efficiency during the degradation of many substrates suggest that fungi provide the bacteria with resources that the bacteria were not able to acquire on their own, most probably intermediate decomposition products released by fungi that could be used by bacteria.

Keywords
antagonism/synergism, bacteria, extracellular enzyme activiy, freshwater-ecosystem litter degradation, fungi, leaf decomposition
National Category
Biological Sciences
Identifiers
urn:nbn:se:uu:diva-92969 (URN)10.1890/0012-9658(2006)87[2559:IOBAFO]2.0.CO;2 (DOI)000241557900016 ()17089664 (PubMedID)
Available from: 2005-04-29 Created: 2005-04-29 Last updated: 2017-12-14Bibliographically approved
4. Contribution of fungi and bacteria to the formation of dissolved organic carbon from decaying common reed (Phragmites australis)
Open this publication in new window or tab >>Contribution of fungi and bacteria to the formation of dissolved organic carbon from decaying common reed (Phragmites australis)
2006 (English)In: Archiv für Hydrobiologie, ISSN 0003-9136, Vol. 166, no 1, p. 79-97Article in journal (Refereed) Published
Abstract [en]

We examined release and subsequent utilization of DOC from leaves of common reed (Phragmites australis), a macrophyte which often dominates in shallow lakes and constitutes an important source of dissolved organic carbon (DOC). Leaves were incubated submersed in organic-free water for up to 63 days with natural and manipulated microbial communities. By this, we aimed to demonstrate differential effects of bacteria and fungi on the composition and amount of DOC originating from the leaves. DOC was analyzed by its total amount, spectral properties at wavelengths of 250-500 nm and its composition determined by size exclusion chromatography followed by organic carbon detection. Leaching of DOC was fast and the maximum DOC concentration was reached after 48 h. Mean molecule size increased during the first 14 days of incubation. Later on, humic-like substances accumulated, whereas low- and high-molecular-weight DOC were depleted. The formation of DOC from leaf detritus was strongly influenced by the composition of the microbial community present. Bacteria effectively removed low-molecular-weight DOC and accumulated high-molecular-weight DOC during a 7 day incubation. Leaf-degrading fungi promoted the accumulation of high amounts of intermediate-molecular-weight DOC, but were suppressed by the presence of bacteria. The presence of bacteria and/or fungi thus resulted in contrasting patterns of DOC composition, suggesting functional differences and strong interactions between those two major microbial groups during natural decomposition of leaves. The activity and interactions of both groups may therefore be significant for DOC composition in aquatic systems.

National Category
Biological Sciences
Identifiers
urn:nbn:se:uu:diva-92970 (URN)10.1127/0003-9136/2006/0166-0079 (DOI)000238757500005 ()
Available from: 2005-04-29 Created: 2005-04-29 Last updated: 2017-12-14Bibliographically approved
5. Litter-associated bacteria and fungi – a comparison of biomass and communities across lakes and plant species
Open this publication in new window or tab >>Litter-associated bacteria and fungi – a comparison of biomass and communities across lakes and plant species
In: Article in journal (Refereed) Submitted
Identifiers
urn:nbn:se:uu:diva-92971 (URN)
Available from: 2005-04-29 Created: 2005-04-29 Last updated: 2017-11-30Bibliographically approved
6. Ergosterol as a measure of living fungal biomass: persistence in environmental samples after fungal death
Open this publication in new window or tab >>Ergosterol as a measure of living fungal biomass: persistence in environmental samples after fungal death
2004 In: Journal of Microbiological Methods, ISSN 0167-7012, Vol. 59, no 2, p. 253-262Article in journal (Refereed) Published
Identifiers
urn:nbn:se:uu:diva-92972 (URN)
Available from: 2005-04-29 Created: 2005-04-29Bibliographically approved

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