Allelopathic Interactions between Cyanobacteria and Dinoflagellates - Rapid Naiadinium polonicum decline in co-culture with Microcystis sp.
(2023) BION02 20231Degree Projects in Biology
- Abstract
- The frequency of harmful algal blooms is increasing steadily, and every summer there are phycotoxins compromising the quality of freshwater ecosystems. Although this is of rising concern, the mechanisms behind harmful algal blooms are not yet fully understood. Cyanobacteria are the usual culprits, while freshwater dinoflagellates have generally been considered non-toxic, though toxic blooms of freshwater dinoflagellates have been reported on a few occasions. In Lake Vombsjön, Sweden, the cyanobacterium Microcystis sp. typically dominates summer bloom events. In 2018, however, there was a shift in the summer phytoplankton community and the potentially toxic dinoflagellate, Naiadinium polonicum, dominated. One mechanism that may have... (More)
- The frequency of harmful algal blooms is increasing steadily, and every summer there are phycotoxins compromising the quality of freshwater ecosystems. Although this is of rising concern, the mechanisms behind harmful algal blooms are not yet fully understood. Cyanobacteria are the usual culprits, while freshwater dinoflagellates have generally been considered non-toxic, though toxic blooms of freshwater dinoflagellates have been reported on a few occasions. In Lake Vombsjön, Sweden, the cyanobacterium Microcystis sp. typically dominates summer bloom events. In 2018, however, there was a shift in the summer phytoplankton community and the potentially toxic dinoflagellate, Naiadinium polonicum, dominated. One mechanism that may have contributed to the shift in the phytoplankton community is allelopathy, i.e., the release of secondary metabolites by phytoplankton that are harmful to other phytoplankton. This study investigated possible allelopathic interactions between Microcystis sp. and N. polonicum through batch culture experiments. In the first set-up there was no cell-to-cell contact, as each species was exposed to the cell-free supernatant of the other, whereas during the second set-up they were grown in co-cultures. A vast reduction of 99% of N. polonicum cells were observed when the two species were grown together, implicating that allelopathy may contribute to the ability of Microcystis sp. to outcompete N. polonicum, but only when there is cell-to-cell contact. There was, however, no evidence that N. polonicum had a negative effect on Microcystis sp. and allelopathy is therefore unlikely to explain the shift in the phytoplankton community that occurred in 2018 in Lake Vombsjön. (Less)
- Popular Abstract
- To Bloom or Not to Bloom
Have you ever seen a completely green lake during summer? These phenomena are called harmful algal blooms, and their frequency is increasing steadily. Unfortunately, they threaten our aquatic ecosystems and cause socioeconomic as well as health issues for us humans. The culprits of harmful algal blooms are dominant algae species that grow to large numbers and leave no room for other species. On top of that, many of these species release toxins and other biochemical products into their environment, which can have lethal effects on organisms in lakes, but also on pets and humans.
One group of biochemicals that algae use in competition with other species are allelochemicals. Many are harmless to us and most... (More) - To Bloom or Not to Bloom
Have you ever seen a completely green lake during summer? These phenomena are called harmful algal blooms, and their frequency is increasing steadily. Unfortunately, they threaten our aquatic ecosystems and cause socioeconomic as well as health issues for us humans. The culprits of harmful algal blooms are dominant algae species that grow to large numbers and leave no room for other species. On top of that, many of these species release toxins and other biochemical products into their environment, which can have lethal effects on organisms in lakes, but also on pets and humans.
One group of biochemicals that algae use in competition with other species are allelochemicals. Many are harmless to us and most inhabitants of the lakes, like fish and snails, but are extremely harmful to specific algae species. They might for instance attack the structure of cell membranes, disturb their photosynthetic activity or lead to death of the cell. Allelochemicals are vast and difficult to identify, even with modern techniques, which is why it is a field of research that has the potential to offer many new discoveries in the future. For us it will be beneficial to know more about allelochemical interactions between algae species, so that we learn more about the aquatic ecosystems that we love and depend on.
Lake Vombsjön, a lake in Southern Sweden, often experiences harmful algal blooms that are dominated by a species of cyanobacteria known to produce harmful toxins. This is problematic, because Lake Vombsjön supplies drinking water to more than 400 000 Swedish citizens. In the past years, however, the dominant cyanobacterium, Microcystis sp., has been outcompeted by a dinoflagellate, Naiadinium polonicum, on multiple occasions resulting in a clear presence/absence pattern of these species. We do not know, however, why they take such turns. In this study, I investigated whether the reason might be found in allelochemical interactions between the two species.
Both species were used as a donor as well as a target, meaning that the donor is the producer of potential allelochemicals and the target is the species that is potentially a victim of the allelochemicals. I performed multiple experiments lasting between two and six days. The main difference between experimental set-ups were that, one set-up allowed the two species to be in direct contact with each other, whereas cells were strictly isolated from one another in the other set-up. The species were represented by two strains each, which accounted for genetic variability.
My results provide evidence that there are negative allelopathic effects between Microcystis sp. and N. polonicum. When the two species grew together, I observed a rapid decrease of N. polonicum cells. Their cells were barely detectable after sharing an environment with Microcystis sp. for six days, and those that survived had an altered morphology. The cyanobacterium on the other hand grew even better and seemed to profit from having N. polonicum as a roommate. This new knowledge may help us understand how the cyanobacterium establishes dominance over the dinoflagellates in Lake Vombsjön. However, the question remains how exactly the allelochemical is acting and furthermore, how N. polonicum forms blooms and sometimes wins the race against its dangerous opponent.
Master’s Degree Project in Biology 45 credits 2023
Department of Biology, Lund University
Advisors: Karin Rengefors and Sandra Rabow
Unit of Aquatic Ecology (Less)
Please use this url to cite or link to this publication:
http://lup.lub.lu.se/student-papers/record/9141482
- author
- Hüller, Jana
- supervisor
-
- Karin Rengefors LU
- Sandra Rabow LU
- organization
- course
- BION02 20231
- year
- 2023
- type
- H2 - Master's Degree (Two Years)
- subject
- language
- English
- id
- 9141482
- date added to LUP
- 2023-11-15 11:11:51
- date last changed
- 2023-11-15 11:11:51
@misc{9141482,
abstract = {{The frequency of harmful algal blooms is increasing steadily, and every summer there are phycotoxins compromising the quality of freshwater ecosystems. Although this is of rising concern, the mechanisms behind harmful algal blooms are not yet fully understood. Cyanobacteria are the usual culprits, while freshwater dinoflagellates have generally been considered non-toxic, though toxic blooms of freshwater dinoflagellates have been reported on a few occasions. In Lake Vombsjön, Sweden, the cyanobacterium Microcystis sp. typically dominates summer bloom events. In 2018, however, there was a shift in the summer phytoplankton community and the potentially toxic dinoflagellate, Naiadinium polonicum, dominated. One mechanism that may have contributed to the shift in the phytoplankton community is allelopathy, i.e., the release of secondary metabolites by phytoplankton that are harmful to other phytoplankton. This study investigated possible allelopathic interactions between Microcystis sp. and N. polonicum through batch culture experiments. In the first set-up there was no cell-to-cell contact, as each species was exposed to the cell-free supernatant of the other, whereas during the second set-up they were grown in co-cultures. A vast reduction of 99% of N. polonicum cells were observed when the two species were grown together, implicating that allelopathy may contribute to the ability of Microcystis sp. to outcompete N. polonicum, but only when there is cell-to-cell contact. There was, however, no evidence that N. polonicum had a negative effect on Microcystis sp. and allelopathy is therefore unlikely to explain the shift in the phytoplankton community that occurred in 2018 in Lake Vombsjön.}},
author = {{Hüller, Jana}},
language = {{eng}},
note = {{Student Paper}},
title = {{Allelopathic Interactions between Cyanobacteria and Dinoflagellates - Rapid Naiadinium polonicum decline in co-culture with Microcystis sp.}},
year = {{2023}},
}