Abstract
Benthic Phormidium mats can contain high concentrations of the neurotoxins anatoxin-a and homoanatoxin-a. However, little is known about the co-occurrence of anatoxin-producing and non-anatoxin-producing strains within mats. There is also no data on variation in anatoxin content among toxic genotypes isolated from the same mat. In this study, 30 Phormidium strains were isolated from 1 cm2 sections of Phormidium-dominated mats collected from three different sites. Strains were grown to stationary phase and their anatoxin-a, homoanatoxin-a, dihydroanatoxin-a and dihydrohomoanatoxin-a concentrations determined using liquid chromatography-mass spectrometry. Each strain was characterized using morphological and molecular (16S rRNA gene sequences) techniques. Eighteen strains produced anatoxin-a, dihydroanatoxin-a or homoanatoxin-a. Strains isolated from each mat either all produced toxins, or were a mixture of anatoxin and non-anatoxin-producing genotypes. Based on morphology these genotypes could not be separated. The 16S rRNA gene sequence comparisons showed a difference of at least 17 nucleotides among anatoxin and non-anatoxin-producing strains and these formed two separate sub-clades during phylogenetic analysis. The total anatoxin concentration among toxic strains varied from 2.21 to 211.88 mg kg−1 (freeze dried weight), representing a 100 fold variation in toxin content. These data indicate that both the relative abundance of anatoxin and non-anatoxin-producing genotypes, and variations in anatoxin producing capability, can influence the overall toxin concentration of benthic Phormidium mat samples.
Highlights
Phormidium is a cyanobacterium that can form expansive benthic mats on the substrata of lakes and rivers [1,2,3]
In this study we investigated the toxin producing abilities of 30 Phormidium strains isolated from four anatoxin-containing mats collected from three different sites
The results of this study demonstrate, for the first time, the coexistence of anatoxin- and non-anatoxin-producing Phormidium strains within small (1 cm2) regions of benthic mats
Summary
Phormidium is a cyanobacterium that can form expansive benthic mats on the substrata of lakes and rivers [1,2,3]. Benthic proliferations dominated by Phormidium are of concern because some strains produce the potent neurotoxic compounds anatoxin-a, dihydroanatoxin-a, homoanatoxin-a, and dihydrohomoanatoxin-a, hereafter collectively referred to as anatoxins [1,2,4]. Anatoxins are powerful neuromuscular blocking agents that act through the nicotinic acetylcholine receptor. They bind to acetylcholine receptors triggering muscle contraction or other neural signal responses. They cannot be broken down by acetylcholine esterase and cause over-stimulation.
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