Impact of a sulfonylureic herbicide on growth of photosynthetic and non-photosynthetic protozoa

Abstract

We studied the impact of a sulfonylurea-based herbicide on the growth of aquatic microbes including photosynthetic and non-photosynthetic protozoa, and ex-symbiotic and non-symbiotic free living algae. This herbicide is designed to block the biosynthesis of branched amino acids in plants. A commercial sulfonylurea-based herbicide containing methyl 3-[[(4-methoxy-6-methyl-1,3,5- triazin-2-yl)carbamoyl]-sulfamoyl]-2-thiophenecarboxylate was added to the culture of Paramecium trichium, P. caudatum, P. bursaria (green paramecia), and Euglena gracilis, an ex-symbiotic algae isolated from green paramecia and free-living Chlorella, at various concentrations ranging from 0.01 to 1 000 mg l-1. The viability of protozoa and algae was examined under microscopy, 1 week after addition of the herbicide. High concentrations of herbicide (100-300 mg l-1) were shown to be inhibitory to the growth of symbiotic algae and free living Chlorella. The same range of herbicide concentrations was shown to be at lethal level for green paramecia and other non-photosynthetic paramecia. The herbicide showed no lethal effect in Euglena gracilis. Instead, the growth in Euglena gracilis was markedly enhanced. In addition, treatment with the herbicide resulted in marked changes in size and shape of the Euglena cells seriously affecting the euglenoid movement. Lastly we conclude that the sulfonylureic herbicides may not be harmless to aqueous environment. © 2005 Springer-Verlag Berlin Heidelberg.