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The neurotoxin β-N-methylamino-L-alanine (BMAA): Sources, bioaccumulation and extraction procedures
Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

β-methylamino-L-alanine (BMAA) is a neurotoxin linked to neurodegeneration, which is manifested in the devastating human diseases amyotrophic lateral sclerosis, Alzheimer’s and Parkinson’s disease. This neurotoxin is known to be produced by almost all tested species within the cyanobacterial phylum including free living as well as the symbiotic strains. The global distribution of the BMAA producers ranges from a terrestrial ecosystem on the Island of Guam in the Pacific Ocean to an aquatic ecosystem in Northern Europe, the Baltic Sea, where annually massive surface blooms occur. BMAA had been shown to accumulate in the Baltic Sea food web, with highest levels in the bottom dwelling fish-species as well as in mollusks.

One of the aims of this thesis was to test the bottom-dwelling bioaccumulation hypothesis by using a larger number of samples allowing a statistical evaluation. Hence, a large set of fish individuals from the lake Finjasjön, were caught and the BMAA concentrations in different tissues were related to the season of catching, fish gender, total weight and species. The results reveal that fish total weight and fish species were positively correlated with BMAA concentration in the fish brain. Therefore, significantly higher concentrations of BMAA in the brain were detected in plankti-benthivorous fish species and heavier (potentially older) individuals.

Another goal was to investigate the potential production of BMAA by other phytoplankton organisms. Therefore, diatom cultures were investigated and confirmed to produce BMAA, even in higher concentrations than cyanobacteria. All diatom cultures studied during this thesis work were show to contain BMAA, as well as one dinoflagellate species. This might imply that the environmental spread of BMAA in aquatic ecosystems is even higher than previously thought.

Earlier reports on the concentration of BMAA in different organisms have shown highly variable results and the methods used for quantification have been intensively discussed in the scientific community. In the most recent studies, liquid chromatography-tandem mass spectrometry (LC-MS/MS) has become the instrument of choice, due to its high sensitivity and selectivity. Even so, different studies show quite variable concentrations of BMAA. In this thesis, three of the most common BMAA extraction protocols were evaluated in order to find out if the extraction could be one of the sources of variability. It was found that the method involving precipitation of proteins using trichloroacetic acid gave the best performance, complying with all in-house validation criteria. However, extractions of diatom and cyanobacteria cultures with this validated method and quantified using LC-MS/MS still resulted in variable BMAA concentrations, which suggest that also biological reasons contribute to the discrepancies.

The current knowledge on the environmental factors that can induce or reduce BMAA production is still limited. In cyanobacteria, production of BMAA was earlier shown to be negative correlated with nitrogen availability – both in laboratory cultures as well as in natural populations. Based on this observation, it was suggested that in unicellular non-diazotrophic cyanobacteria, BMAA might take part in nitrogen metabolism. In order to find out if BMAA has a similar role in diatoms, BMAA was added to two diatom species in culture, in concentrations corresponding to those earlier found in the diatoms. The results suggest that BMAA might induce a nitrogen starvation signal in diatoms, as was earlier observed in cyanobacteria. However, diatoms recover shortly by the extracellular presence of excreted ammonia. Thus, also in diatoms, BMAA might be involved in the nitrogen balance in the cell.

Place, publisher, year, edition, pages
Stockholm: Department of Ecology, Environment and Plant Sciences, Stockholm University , 2016. , 69 p.
National Category
Biological Sciences
Research subject
Plant Physiology
Identifiers
URN: urn:nbn:se:su:diva-132142ISBN: 978-91-7649-455-4 (print)OAI: oai:DiVA.org:su-132142DiVA: diva2:949423
Public defence
2016-09-22, Vivi Täckholmsalen (Q-salen), NPQ-huset, Svante Arrhenius väg 20, Stockholm, 10:00 (English)
Opponent
Supervisors
Funder
Swedish Research Council Formas
Note

At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 4: Manuscript.

Available from: 2016-08-30 Created: 2016-07-19 Last updated: 2016-08-31Bibliographically approved
List of papers
1. Biotransfer of beta-N-Methylamino-l-alanine (BMAA) in a Eutrophicated Freshwater Lake
Open this publication in new window or tab >>Biotransfer of beta-N-Methylamino-l-alanine (BMAA) in a Eutrophicated Freshwater Lake
2015 (English)In: Marine Drugs, ISSN 1660-3397, E-ISSN 1660-3397, Vol. 13, no 3, 1185-1201 p.Article in journal (Refereed) Published
Abstract [en]

beta-N-Methylamino-l-alanine (BMAA), a neurotoxic non-protein amino acid, plays a significant role as an environmental risk factor in neurodegenerative diseases, such as amyotrophic lateral sclerosis. BMAA producers occur globally, colonizing almost all habitats and represent species from distinct phytoplanktonic groups, i.e., cyanobacteria, diatoms, and dinoflagellates. Bioaccumulation of BMAA in invertebrate and vertebrate organisms has also been registered around the globe. In the Baltic Sea, BMAA has been detected in several commercial fish species, raising the question of the bioaccumulation of BMAA in Swedish limnic systems. Here we find the presence of BMAA in water samples from Lake Finjasjon and identify its bioaccumulation patterns in both plankti-benthivorous and piscivorous fish, according to fish species, total weight, gender, and season of collection. For the first time, a large number of fish individuals were used in order to draw conclusions on BMAA bioaccumulation in a closed ecological community based on a statistical approach. We may, therefore, conclude that feeding patterns (plankti-benthivorous) and increased age of fish may lead to a higher tissue concentration of BMAA.

National Category
Biological Sciences
Research subject
Plant Physiology
Identifiers
urn:nbn:se:su:diva-117017 (URN)10.3390/md13031185 (DOI)000351930500006 ()25738330 (PubMedID)
Note

AuthorCount:4;

Available from: 2015-05-06 Created: 2015-05-05 Last updated: 2017-12-04Bibliographically approved
2. Diatoms: A Novel Source for the Neurotoxin BMAA in Aquatic Environments
Open this publication in new window or tab >>Diatoms: A Novel Source for the Neurotoxin BMAA in Aquatic Environments
Show others...
2014 (English)In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 9, no 1, e84578Article in journal (Refereed) Published
Abstract [en]

Amyotrophic lateral sclerosis (ALS) or Lou Gehrig's disease is a neurological disorder linked to environmental exposure to a non-protein amino acid, beta-N-methylamino-L-alanine (BMAA). The only organisms reported to be BMAA-producing, are cyanobacteria - prokaryotic organisms. In this study, we demonstrate that diatoms - eukaryotic organisms - also produce BMAA. Ultra-high-performance liquid chromatography coupled with tandem mass spectrometry revealed the occurrence of BMAA in six investigated axenic diatom cultures. BMAA was also detected in planktonic field samples collected on the Swedish west coast that display an overrepresentation of diatoms relative to cyanobacteria. Given the ubiquity of diatoms in aquatic environments and their central role as primary producers and the main food items of zooplankton, the use of filter and suspension feeders as livestock fodder dramatically increases the risk of human exposure to BMAA-contaminated food.

National Category
Biological Sciences Analytical Chemistry
Research subject
Analytical Chemistry; Plant Physiology
Identifiers
urn:nbn:se:su:diva-100864 (URN)10.1371/journal.pone.0084578 (DOI)000329460100066 ()
Note

AuthorCount:8;

Available from: 2014-02-19 Created: 2014-02-17 Last updated: 2017-12-06Bibliographically approved
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