Abstract
The Nostoc genus is a well-known heterocytous, filamentous cyanobacterium which can be found all over the world. The size of terrestrial and/or freshwater colonies can be microscopic and macroscopic as well. In addition, Nostoc species are one of the most common photosynthetic cyanobacterial partners in symbiotic interactions. Terrestrial cyanobacterial colonies were collected and isolated in this study from various alkali grassland habitats (Great Hungarian Plain). Altogether 133 colonies were isolated from the 65 collected samples. The peptide patterns of the Nostoc-like strains were examined using HPLC-ESI-MS/MS and 41 peptides were identified from 45 isolated Nostoc-like strains; these compounds belonged to 4 different peptide classes. Twelve nostoginin/microginin, 16 anabaenopeptin, 12 banyaside/suomilide variants were identified. 37% of our isolated Nostoc-like strains produced some of the peptide metabolites we tested. These strains showed distinct chemotypes according to their peptide patterns, and can be divided into 4 groups based on their metabolisms. Strains either contained: (1) nostoginins/microginins, (2) anabaenopeptins, (3) anabaenopeptins and banyasides or (4) banyasides as major compounds. Banyasides were present in many of our strains and showed very high intensity in some cases. A number of previously unknown banyaside variants have been identified.
Highlights
Cyanobacteria are a highly diverse group of photosynthetic gramnegative prokaryotes
The main objective of this work was the: (i) determination of the main chemotypes of the Nostoc species occurring on Hungarian alkaline grasslands; and (ii) identification of well-known and new cyanotoxins and bioactive cyanopeptides produced by Nostoc species with non-targeted LC-MS based method
There are no exact comparative studies between terrestrial and a pelagic cyanobacteria about the peptide producing ability/peptide content neither in the Nostoc nor in the other genus, our results suggest that these studied terrestrial Nostoc spp. contained less diverse and fewer amount of peptide metabolites compared to other freshwater species (e.g. Microcystis sp., Planktothrix sp.) [103,104,105,106]
Summary
Cyanobacteria are a highly diverse group of photosynthetic gramnegative prokaryotes They can be found in a wide range of habitats (freshwater, marine and terrestrial ecosystems) and are able to adapt to special circumstances such as high UV levels, extreme temperatures and pH conditions [1,2,3,4]. Their organization can be unicellular, colonial or filamentous and they can be spherical, rod and spiral shaped. Several new genera and species within family Nostocaceae have been described in the last years including the reclassification of some Nostoc isolates, the taxonomic identification of Nostoc-like strains is still controversial due to the incongruences between morphological characters and phylogenetic data [7,8]
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