Abstract
Heterocytous cyanobacteria are among the most prolific sources of bioactive secondary metabolites, including anabaenopeptins (APTs). A terrestrial filamentous Brasilonema sp. CT11 collected in Costa Rica bamboo forest as a black mat, was studied using a multidisciplinary approach: genome mining and HPLC-HRMS/MS coupled with bioinformatic analyses. Herein, we report the nearly complete genome consisting of 8.79 Mbp with a GC content of 42.4%. Moreover, we report on three novel tryptophan-containing APTs; anabaenopeptin 788 (1), anabaenopeptin 802 (2), and anabaenopeptin 816 (3). Furthermore, the structure of two homologues, i.e., anabaenopeptin 802 (2a) and anabaenopeptin 802 (2b), was determined by spectroscopic analysis (NMR and MS). Both compounds were shown to exert weak to moderate antiproliferative activity against HeLa cell lines. This study also provides the unique and diverse potential of biosynthetic gene clusters and an assessment of the predicted chemical space yet to be discovered from this genus.
Highlights
For 3.5 billion years, cyanobacteria have kept developing new adaptation features and defense mechanisms which allowed them to colonize the earth, shape its atmosphere from anoxic to oxygenic, and ever since to survive in harsh and strongly competitive environments under extreme temperatures, salt stress, high UV-radiation, and pathogen attack [1,2]
Molecules 2020, 25, 3786 populations known as cyanobacterial blooms (CBs), which can be harmful for aquatic life as well as for human health because of the toxins they produce [8,9]
Cyanobacteria comprise a wide range of phylogenetic lineages, of which the monophyletic order Nostocales are an extremely competent group in terms of general secondary metabolite production [10]
Summary
For 3.5 billion years, cyanobacteria have kept developing new adaptation features and defense mechanisms which allowed them to colonize the earth, shape its atmosphere from anoxic to oxygenic, and ever since to survive in harsh and strongly competitive environments under extreme temperatures, salt stress, high UV-radiation, and pathogen attack [1,2] One of these survival strategies is the production of a vast variety of secondary metabolites, exhibiting a broad spectrum of biological activities and properties, including peptides, lipopeptides, polyketides, alkaloids, lipids, and terpenoids [3,4,5,6,7]. Filamentous cyanobacteria, in particular the genera Anabaena, Nostoc, Oscillatoria, and Lyngbya, produce a large variety of secondary metabolites, estimated to account for approximately 25% of the total number of known cyanobacterial metabolites [11,12,13,14]. The combined approach of genome mining and HPLC-HRMS/MS coupled with bioinformatic analyses led us to identify four unusual novel tryptophan-containing APTs showing moderate antiproliferative activity
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