Biomedical subjects
Peter Henriksen
Publications and source records attributed to Peter Henriksen.
[ADMAdda5]-microcystins in Planktothrix agardhii strain PH-123 (cyanobacteria)--importance for monitoring of microcystins in the environment.
Two major and two minor microcystins (MCYST) were isolated from a hepatotoxic Danish strain of Planktothrix agardhii (Gomont) Anagnostidis et Komárek by reversed-phase high-performance liquid chromatography. The microcystins were characterized by UV spectroscopy, amino acid analysis, fast atom bombardment mass spectrometry (FABMS), and high-resolution FABMS. The major microcystins were further analysed by collisionally induced tandem electrospray ionization MS. The microcystins were found to be demethylated variants of MCYST-HtyR (homotyrosine-arginine) and MCYST-LR (leucine-arginine). The two major microcystins contained an acetyl-demethyl variant (ADMAdda) of 3-amino-9-acetoxy-2,6,8-trimethyl-10-phenyldeca-4,6-dienoic acid (Adda). This is the first report of [ADMAdda5]-microcystins in Planktothrix. The two [ADMAdda5]-microcystins inhibited protein phosphatase activity but showed low cross-reactivity with antibodies of an enzyme-linked immunosorbent assay (ELISA), emphasizing the potential underestimation of the toxicity of natural blooms dominated by Planktothrix when microcystin content is quantified using only an ELISA.
Phylogenetic comparison of the cyanobacterial genera Anabaena and Aphanizomenon.
Morphological analysis and sequencing of the 165 rRNA gene, the spacer region of the ribosomal operon (ITS1) and the rbcLX (RubisCO) region was performed on 26 Anabaena strains and 14 Aphanizomenon strains isolated from several lakes in Denmark, Finland and France. Based on their morphology, Anabaena strains differed from strains of Aphanizomenon: the vegetative cells, heterocysts and akinetes were significantly wider in Anabaena than in Aphanizomenon. Phylogenetic trees based on the 16S rDNA, ITS1 and rbcLX regions showed that the planktic Anabaena strains were not distinguishable from Aphanizomenon strains. The results of the clustering of Anabaena and Aphanizomenon strains based on 16S rDNA sequences showed that these two genera are not monophyletic. Sequence analysis of the 16S rDNA, ITS1-S and rbcLX regions of the planktic Anabaena strains showed that this genus is heterogeneous. In all methods, Anabaena strains that produced different toxic compounds (e.g. anatoxin-a, microcystin and an unknown neurotoxin) were clustered separately from each other but were grouped either with non-toxic Anabaena and/or Aphanizomenon strains. Our data suggest that the planktic Anabaena and Aphanizomenon isolates belong to the same genus, regardless of their morphological differences. Thus, a taxonomic revision of the two genera is required.
Detection of anatoxin-a(s) in environmental samples of cyanobacteria by using a biosensor with engineered acetylcholinesterases.
Bioassays are little used to detect individual toxins in the environment because, compared to analytical methods, these assays are still limited by several problems, such as the sensitivity and specificity of detection. We tentatively solved these two drawbacks for detection of anatoxin-a(s) by engineering an acetylcholinesterase to increase its sensitivity and by using a combination of mutants to obtain increased analyte specificity. Anatoxin-a(s), a neurotoxin produced by some freshwater cyanobacteria, was detected by measuring the inhibition of acetylcholinesterase activity. By using mutated enzyme, the sensitivity of detection was brought to below the nanomole-per-liter level. However, anatoxin-a(s) is an organophosphorous compound, as are several synthetic molecules which are widely used as insecticides. The mode of action of these compounds is via inhibition of acetylcholinesterase, which makes the biotest nonspecific. The use of a four-mutant set of acetylcholinesterase variants, two mutants that are sensitive to anatoxin-a(s) and two mutants that are sensitive to the insecticides, allows specific detection of the cyanobacterial neurotoxin.