Microbiotests for Cyanobacterial Toxins Screening
Abstract : The development of massive blooms of cyanobacteria (blue-green algae) in eutrophicated fresh and salt waters is an actual problem in many countries. Moreover, many strains of cyanobacteria produce toxins with a specific mode of action, the most studied being hepatotoxins (such as e.g. microcystin) and neurotoxins (e.g. anatoxin-a). Toxicity testing of crude extracts of cyanobacterial biomass often causes problems of interpretation of results because of the presence of many compounds interfering with the detection and the quantification of observed effects. A fractionation technique based on SPE C-18 cartridges was developed allowing to separate and recover fractions selectively containing cyanobacterial hepatotoxins. Two samples of cyanobacterial biomass (both crude extract and toxic fraction) were tested for toxicity with a battery of 7 different toxicity microbiotests with different test organisms : bacteria, ciliate protozoans, rotifers, crustanceans and nematodes. In addition, one mutagenic bacterial microbioassay was also applied. Samples were selected on the basis of the content of cyanobacterial hepatotoxin microcystin-LR (high content vs. absence). The toxic data of the crude extracts were compared with those of the water and toxin fractions.
The outcome of the study revealed that the crustacean microbiotests were by far the most discriminative for toxicity detection between non-toxic and toxic samples, and that the Thamnotoxkit F™ assay was the most sensitive bioassay within the battery. The study also showed that fractionation of the crude extract of cyanobacterial biomass allows to distinguish toxic effects of the hepatotoxins proper from those of other toxic compounds present in the crude extract.