Selective toxicity of exogenous l-lysine to cyanobacteria, relative to a chlorophyte and a diatom

Abstract

Autotrophic and heterotrophic nitrogen assimilation supports algal growth. Recently, however, Kaya & Sano [Phycologia 35 (6, supplement): 117–119 (1996)] reported that < l mg l−1 of either D-or L-lysine completely inhibited the growth of Microcystis sp. We investigated the effects of increasing lysine additions on cultures of cyanobacteria, a chlorophyte and a diatom. In contrast to the previous report by Kaya & Sano, D-lysine (400 mg l−1) had no effect on chlorophyll a accumulation by any taxa tested. L-lysine inhibited Chl a accumulation by Microcystis aeruginosa, Pseudanabaena articulata and Planktothrix perornata (Cyanobacteria) and 2-methylisoborneol accumulation by Pseudanabaena articulata and Planktothrix perornata. However, concentrations > l mg l−1 were required for inhibition. Additions of < 400 mg l−1 of lysine did not significantly reduce Chl a accumulation by Scenedesmus dimorphus(Chlorophyta). Cyclotella meneghiniana (Bacillariophyta) was not affected by 400 mg l−1 L-lysine additions. The mechanisms of inhibition of Chl a accumulation in cyanobacteria are unknown. However, the effects of L-lysine were decreased when the inoculum concentration was increased. This and the isomeric specificity of inhibition suggest that exogenous L-lysine may inhibit enzymatic processes. Differential inhibition among taxa could potentially alter the proportion of cyanobacteria in mixed algal assemblages.