Changes in oligopeptide production by toxic cyanobacterial strains under iron deficiency

Abstract

Cyanobacteria produce several peptides whose functions and regulation mechanisms are not well understood. Iron availability has previously been suggested as a potential factor controlling production of microcystin, the best studied of these peptides, although results were not always consistent. Here, we examined how production of several peptides by 3 cyanobacterial strains changed in response to iron starvation or limitation. Experiments were run with 2 strains of Radiocystis fernandoii (28 and 86) and one of Planktothrix agardhii (27). The peptide spectra were analyzed and the gene expression of 2 peptides was assessed. Under iron starvation (no iron) all microcystin variants and one cyanopeptolin were significantly reduced in R. fernandoii 28 and P. agardhii 27. Only one compound, anabaenopeptin in P. agardhii 27, increased significantly. The strain R. fernandoii 86 did not show any significant modification in response to iron deprivation. Under moderate limitation, most peptides also decreased, although less abruptly. Conversely, changes in gene expression showed that genes coding for microcystin and aeruginosin were differentially expressed and were significantly higher under iron deprivation. This is consistent with previous findings that suggested that microcystin is produced to overcome stress. The lack of microcystin production despite the increased gene transcription is discussed in light of previous findings. This result might be due to either modifications of the cell metabolic state as a result of shortage of some important enzymes under iron deprivation or to microcystin loss as a result of its binding to proteins or other potential sink sources in the cell.