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The role of allelopathy in microbial food webs
Linnaeus University, Faculty of Science and Engineering, School of Natural Sciences. (marine ecology)
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Phytoplankton produce allelochemicals; excreted chemical substances that are affecting other microorganisms in their direct environment.

In my thesis, I investigated strain specific variability in the expression of allelochemicals of the harmful flagellate Prymnesium parvum, that is euryhaline but mainly bloom forming in brackish water. I found a large variation among strains, but further showed that all strains of P. parvum were more allelopathic in brackish water compared to marine water.

In a marine microbial community, allelochemicals can affect prey, competitors and grazers both, directly and indirectly. For instance, in a food web where grazing controls prey abundance, the negative direct effect of allelochemicals on grazers will positive affect their prey. During my thesis, I investigated how marine microbial communities respond to the addition of allelochemicals. I performed field experiments with microbial communities from seawater collected from different places over Europe, and tested how this communities respond to the addition of allelochemicals from the dinoflagellate Alexandrium tamarense. Before I incubated the microbial communities for several days with A. tamarense algal filtrate, I evaluated the allelopathic efficiency of the algal filtrates with an algal monoculture of Rhodomonas spp. This allowed me to compare the effect of A. tamarense filtrate between the different microbial communities.

In general, bacteria reached higher abundances when allelochemicals were present. As allelochemicals also inhibited nanoflagellates and ciliates, we concluded, that allelochemicals indirectly benefit bacteria by reducing grazing pressure. In microbial food webs with many heterotrophic grazers, allelochemicals further benefitted other phytoplankton by inhibiting grazers.

It was also shown that bioavailable DOM is released from a microbial community when allelochemicals are present. As most DOM was released from the seawater fraction > 60 μm, we concluded, that larger microorganisms are more affected by allelochemicals than smaller microorganisms. The results can be explained by the surface to volume ratio of microorganisms: Larger organisms provide more contact surface for allelochemicals, and therefore, are probably more vulnerable towards allelochemicals.

In conclusion, the effect of allelochemicals on a microbial community depends among others on the structure of the microbial food web, the amount of available DOM, the particle density in the seawater and the composition of the phytoplankton community.

Place, publisher, year, edition, pages
Växjö, Kalmar: Linnaeus University Press , 2011.
Series
Linnaeus University Dissertations, 33/2011
Keyword [en]
Microbial food web, Allelopathy, Alexandrium tamarense, Prymnesium parvum, Infochemicals, marine plankton community
National Category
Ecology
Research subject
Natural Science, Aquatic Ecology
Identifiers
URN: urn:nbn:se:lnu:diva-11375ISBN: 978-91-86491-62-8OAI: oai:DiVA.org:lnu-11375DiVA: diva2:410118
Public defence
2011-03-04, Fullrigarren, Barlastgatan 11, Kalmar, 09:15 (English)
Opponent
Supervisors
Funder
Swedish Research Council
Available from: 2011-04-13 Created: 2011-04-12 Last updated: 2014-05-12Bibliographically approved
List of papers
1. Impact of Alexandrium tamarense allelochemicals on DOM dynamics in an estuarine microbial community
Open this publication in new window or tab >>Impact of Alexandrium tamarense allelochemicals on DOM dynamics in an estuarine microbial community
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2012 (English)In: Harmful Algae, ISSN 1568-9883, E-ISSN 1878-1470, Vol. 13, 58-64 p.Article in journal (Refereed) Published
Abstract [en]

Plankton and dissolved organic carbon (DOC) dynamics in fractionated estuarine microbial communities (<150 μm, <60 μm and <20 μm), incubated with allelopathic (lytic) or non allelopathic (non-lytic) Alexandrium tamarense filtrates were investigated over a period of 48 h. Additionally, the amount of dissolved organic matter (DOM) available for bacterial growth in the treatments was measured via bacterial seawater culture experiments immediately and 6 h after addition of A. tamarense filtrates. The lack of effect on DOC concentrations and plankton community composition in lytic treatments indicated that allelochemicals did not inhibit the growth of the microbial community. Nevertheless, bacterial seawater culture experiments provided evidence that lytic filtrate addition provoked the release of bioavailable DOM from the microbial community. Since DOM was only released from the largest seawater fraction, microorganisms >60 μm were probably most sensitive towards allelochemicals.

Keyword
alexandrium, marine ecology, phytoplankton, bacteria, dissolved organic carbon, allelopathy, microbial food webs
National Category
Ecology
Research subject
Natural Science, Aquatic Ecology; Natural Science, Microbiology
Identifiers
urn:nbn:se:lnu:diva-11370 (URN)10.1016/j.hal.2011.10.003 (DOI)
Projects
ALGBACT
Available from: 2011-04-12 Created: 2011-04-12 Last updated: 2015-12-17Bibliographically approved
2. Hemolytic activity, allelopathy and growth rates of four strains of Prymnesium parvum
Open this publication in new window or tab >>Hemolytic activity, allelopathy and growth rates of four strains of Prymnesium parvum
(English)Manuscript (preprint) (Other academic)
National Category
Natural Sciences
Research subject
Natural Science, Aquatic Ecology
Identifiers
urn:nbn:se:lnu:diva-11374 (URN)
Available from: 2011-04-12 Created: 2011-04-12 Last updated: 2015-09-04Bibliographically approved
3. Phytoplankton allelochemical interactions change microbial food web dynamics
Open this publication in new window or tab >>Phytoplankton allelochemical interactions change microbial food web dynamics
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2011 (English)In: Limnology and Oceanography, ISSN 0024-3590, Vol. 56, 899-909 p.Article in journal (Refereed) Published
Abstract [en]

This study investigates the effect of filtrates from an allelopathic dinoflagellate, Alexandrium tamarense, onfour microbial food webs that have been manipulated experimentally from natural seawater by modifying theavailability of resources in the form of dissolved organic carbon with additions of peptone, and by altering thegrazing pressure with size fractionation. Bacterial production was generally not affected by allelochemicals, butbacteria showed higher net growth in all food webs when allelochemicals were added, whereas heterotrophicnanoflagellates . 7 mm and ciliates were constrained in all food webs. Allelochemicals had the largest negativeeffects on microbial communities with low grazing pressure. In food webs with high grazing pressure andadditional resources, phytoplankton and small nanoflagellates were positively affected by the addition ofallelochemicals, suggesting that those were interfering with trophic interactions in the microbial communities. Bythe lysis of organisms sensitive towards allelochemicals, resources are made available and grazing pressure oncertain microorganisms is reduced. However, the intensity of these interactions is modulated by both theavailability of resources and the biomass of grazers in the initial food web.

Keyword
allelopathy, microbial foodweb, bacteria, Alexandrium, phytoplankton, upwelling
National Category
Ecology
Research subject
Natural Science, Microbiology; Natural Science, Aquatic Ecology
Identifiers
urn:nbn:se:lnu:diva-7334 (URN)10.4319/lo.2011.56.3.0899 (DOI)
Projects
ALGBACTAllelopathy among phytoplankton - a structuring force among phytoplankton
Available from: 2010-08-16 Created: 2010-08-16 Last updated: 2015-09-04Bibliographically approved
4. Allelopathic potential of the dinoflagellate Alexandrium tamarense on marine microbial communities
Open this publication in new window or tab >>Allelopathic potential of the dinoflagellate Alexandrium tamarense on marine microbial communities
2010 (English)In: Harmful Algae, ISSN 1568-9883, E-ISSN 1878-1470, Vol. 10, no 1, 9-18 p.Article in journal (Refereed) Published
Abstract [en]

The impacts of two strains of the dinoflagellate Alexandrium tamarense, differing in lytic activity, on the abundance and the composition of microbial communities (<150 μm) were studied in North Sea water during spring with Phaeocystis globosa as a dominant species. Cell-free suspensions (supernatant) of exponentially growing lytic and non-lytic Alexandrium culture were added at different concentrations to natural microbial communities under nutrient rich conditions. The non-lytic strain had a positive impact on diatoms whereas the lytic strain suppressed phytoplankton growth in comparison to the control. P. globosa, present as single cells in the initial community, increased in abundance and formed colonies in all treatments. However, total abundance and number of colonies was low with lytic Alexandriumadditions, whereas shape of the colonies, but not abundance of cells, was affected by non-lytic Alexandrium additions. During the 4-day experiment, bacterial abundance was constantly higher with high lytic additions (highest concentration equivalent to 1000 cells ml−1) whereas nanoflagellate abundance in the same treatments was found to be lower at the end of the experiment. Initial bacterial community composition differed significantly among lytic Alexandrium, non-lyticAlexandrium and North Sea water. However, neither bacterial activity nor composition was significantly affected by the supernatants after 96 h. Our results indicated that Alexandrium allelochemicals do not inhibit growth and production of bacteria in seawater collected during spring in the North Sea.

Place, publisher, year, edition, pages
Elsevier, 2010
Keyword
Alexandrium spp.; Allelopathy; Algae; Bacteria; North Sea;
National Category
Ecology
Research subject
Natural Science, Aquatic Ecology; Natural Science, Microbiology
Identifiers
urn:nbn:se:lnu:diva-7332 (URN)10.1016/j.hal.2010.05.007 (DOI)000283965700002 ()
Projects
Allelopathy among phytoplankton - a structuring force among phytoplankton
Available from: 2010-09-03 Created: 2010-08-16 Last updated: 2015-09-04Bibliographically approved

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