Evidence that sulfur metabolism plays a role in microcystin production by Microcystis aeruginosa

Microcystins (MCs) are highly toxic, non-ribosomal cyclic peptides produced by cyanobacteria. A wide range of environmental factors are known to affect MC production, yet the roles these factors play in MC metabolism are poorly understood. In this study a physiological role for sulfur in MC synthesis is proposed. Rates of amino acid and MC-LR production were determined from N-limited chemostat grown cells of the toxic cyanobacterium Microcystis aeruginosa MASH-01A19. Cluster analysis of these rates indicated a correlation between the rates of methionine and MC-LR production, suggesting that a competitive physiological requirement for this sulfur-containing metabolite may limit MC-LR production in this organism. In support of this hypothesis, sulfur limitation in batch cultures led to an approximate 1.5-fold decrease in the intracellular MC-LR quota (QMC) over the entire growth cycle, revealing a requirement for sulfur in MC production and suggesting that metabolic demand for methionine may limit MC synthesis.