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

Abstract

Liverwort Blasia pusilla L. recruits soil nitrogen-fixing cyanobacteria of genus Nostoc as symbiotic partners. In this work we compared Nostoc community composition inside the plants and in the soil around them from two distant locations in Northern Norway. STRR fingerprinting and 16S rDNA phylogeny reconstruction showed a remarkable local diversity among isolates assigned to several Nostoc clades. An extensive web of negative allelopathic interactions was recorded at an agricultural site, but not at the undisturbed natural site. The cell extracts of the cyanobacteria did not show antimicrobial activities, but four isolates were shown to be cytotoxic to human cells. The secondary metabolite profiles of the isolates were mapped by MALDI-TOF MS, and the most prominent ions were further analyzed by Q-TOF for MS/MS aided identification. Symbiotic isolates produced a great variety of small peptide-like substances, most of which lack any record in the databases. Among identified compounds we found microcystin and nodularin variants toxic to eukaryotic cells. Microcystin producing chemotypes were dominating as symbiotic recruits but not in the free-living community. In addition, we were able to identify several novel aeruginosins and banyaside-like compounds, as well as nostocyclopeptides and nosperin.

High-Density Cultivation of Terrestrial Nostoc Strains Leads to Reprogramming of Secondary Metabolome

“…As part of this study, we could demonstrate an allelopathic activity against another Nostoc strain for one of the anabaenopeptin variants. These findings support a role of anabaenopeptins in the anticyanobacterial effects observed for strain KVJ2 in a recent study (19). Anabaenopeptins were recently reported to trigger allelopathic effects in cyanobacterial strains of the genus Microcystis (25).…”

“…The HD cultivation approach was further tested with Nostoc sp. strain KVJ2 that was recently isolated from Blasia pusilla in Northern Norway and is phylogenetically distant from N. punctiforme PCC 73102 (19). The strain reached a cell density similar to that reached by strain PCC 73102 (400 g [wet weight]/liter) in a period of 20 days (Fig.…”

“…6B). Notably, anabaenopeptins were not detected in a recent study in which strain KVJ2 was reported to produce only aeruginosin and nostocyclopeptide (19). Indeed, in conventional cultures, anabaenopeptins are virtually absent in extracts of that strain (Fig.…”

“…The metabolite was thus considered a suitable candidate to demonstrate that the increased accumulation of transcripts is indeed reflected at the metabolite level. Anabaenopeptin could not only be identified in much larger amounts in HD extracts of N. punctiforme PCC 73102 but also in the strain KVJ2 that was recently isolated from Blasia pusilla in Northern Norway (19). In both strains, anabaenopeptin production was very low or absent in conventional cultivations, whereas major peaks were detected in HD cultures.…”

“…Since Nostoc sp. strain KVJ2 exhibited allelopathic activities against other Nostoc strains from the same habitat in a recent study (19), 5 g of each anabaenopeptin variant was tested in an allelopathy assay with the sensitive strain Nostoc sp. KVS11.…”