Nodularin, a cyanobacterial toxin, is synthesized in planta by symbiotic Nostoc sp.

Abstract

The nitrogen-fixing bacterium, Nostoc, is a commonly occurring cyanobacterium often found in symbiotic associations. We investigated the potential of cycad cyanobacterial endosymbionts to synthesize microcystin/nodularin. Endosymbiont DNA was screened for the aminotransferase domain of the toxin biosynthesis gene clusters. Five endosymbionts carrying the gene were screened for bioactivity. Extracts of two isolates inhibited protein phosphatase 2A and were further analyzed using electrospray ionization mass spectrometry (ESI-MS)/MS. Nostoc sp. ‘Macrozamia riedlei 65.1’ and Nostoc sp. ‘Macrozamia serpentina 73.1’ both contained nodularin. High performance liquid chromatography (HPLC) HESI-MS/MS analysis confirmed the presence of nodularin at 9.55±2.4 ng μg−1 chlorophyll a in Nostoc sp. ‘Macrozamia riedlei 65.1’ and 12.5±8.4 ng μg−1 Chl a in Nostoc sp. ‘Macrozamia serpentina 73.1’ extracts. Further scans indicated the presence of the rare isoform [L-Har2] nodularin, which contains l-homoarginine instead of l-arginine. Nodularin was also present at 1.34±0.74 ng ml−1 (approximately 3 pmol per g plant ww) in the methanol root extracts of M. riedlei MZ65, while the presence of [L-Har2] nodularin in the roots of M. serpentina MZ73 was suggested by HPLC HESI-MS/MS analysis. The ndaA-B and ndaF genomic regions were sequenced to confirm the presence of the hybrid polyketide/non-ribosomal gene cluster. A seven amino-acid insertion into the NdaA-C1 domain of N. spumigena NSOR10 protein was observed in all endosymbiont-derived sequences, suggesting the transfer of the nda cluster from N. spumigena to terrestrial Nostoc species. This study demonstrates the synthesis of nodularin and [L-Har2] nodularin in a non-Nodularia species and the production of cyanobacterial hepatotoxin by a symbiont in planta.

Diversity of Peptides Produced by Nodularia spumigena from Various Geographical Regions

“…Out of the four classes of oligopeptides, nodularins and spumigins were almost exclusively reported from N. spumigena (with the exceptions described in [28,29,30]). The compounds belonging to aeruginosins and anabaenopeptins were previously detected in different cyanobacterial taxa, including Microcystis , Planktothrix and Anabaena [1].…”

A Genetic and Chemical Perspective on Symbiotic Recruitment of Cyanobacteria of the Genus Nostoc into the Host Plant Blasia pusilla L.

“…Cyanobacteria isolated from symbiotic association with plants and fungi were found to produce a wide spectrum of secondary metabolites. In addition to variety of microcystins from cyanolichens (Kaasalainen et al, 2012) and nodularins from a cycad (Gehringer et al, 2012) there were few other reports suggesting a broad repertoire of secondary metabolites and small peptides in symbiotic Nostoc . Nostopeptolides and anabaenopeptins were found in Nostoc punctiforme PCC73102 (Welker and von Dohren, 2006; Rouhiainen et al, 2010) originally isolated from Macrozamia sp., additionally this particular strain is rich in gene clusters coding for NRPS and hybrid NRPS-PKS metabolites (Ehrenreich et al, 2005) as well ribosomally synthesizes bacteriocin-like and microviridin products (Wang et al, 2011).…”

Cyanotoxins in inland lakes of the United States: Occurrence and potential recreational health risks in the EPA National Lakes Assessment 2007

“…Microcystins have also been measured in Australia, Canada, Denmark, France, Germany, Japan, Portugal, South Africa, and the United Kingdom having microcystin concentrations ranging from <1 to 7100 mg microcystin per g of dry weight biomass. There have been a few other detections of NODR in freshwaters with no apparent producer present , suggesting there may be other, currently unknown NODR producers or perhaps a terrestrial source is possible from inflow events (Gehringer et al, 2012).…”