Metabolite profiling and bioactivity assessment of cyanobacteria from the Azores reveals unique producers of cytotoxic and lipid reducing compounds

Abstract

Cyanobacteria are a group of photosynthetic bacteria and a rich secondary metabolites source. The Bank of Algae and Cyanobacteria of the Azores (BACA) culture collection holds a significant number of strains, including many novel genera and species. 56 strains from freshwater, brackish, and thermal habitats were selected, and grown under standard conditions. Biomass was extracted with methanol, and cytotoxicity was assessed on two carcinoma cell lines, HepG2 and HCT116. The reduction of lipids was tested in zebrafish larvae, and in a steatosis model with fatty acid overloaded human liver cells. The cyanobacterial metabolome was analyzed by HR-ESI-LC-MS/MS and compared using CompareMS2. High similarities were observed in strains of the same genus when isolated from similar habitats, clustering in concordance to the taxonomical order, while no relation could be observed between strains from different genera originated from the same habitat. The extracts of Cyanobium sp. BACA0019, Pseudocalidococcus azoricus BACA0433 and Pegethrix atlantica BACA0077 reduced neutral lipids >40 % in zebrafish at 25 μg/mL, while from Symphyonema sp. BACA0090 and Aliinostoc sp. BACA0355 induced mortality. Lipid reduction in the steatosis model was observed in many strains, with significant results varying from 50 % to 100 %. Several strains reduced cell viability with the strongest effects from Scytonematopsis sp. BACA0005 (HepG2, 59.8 % and HCT116, 68.1 %), Aliinostoc sp. BACA0035 (HepG2, 43.3 %, and HCT116, 59.4 %) and Aliinostoc sp. BACA0355 (HepG2, 46.2 %, and HCT116, 75.5 %). The feature-based molecular networking identified several cluster of mass peaks related to the observed bioactivities. Chlorophyll derivatives and glycerolipids from Cyanobium sp. BACA0019, Pseudocalidococcus azoricus BACA0433 and Pegethrix atlantica BACA0077 were correlated with the reduction of lipids in zebrafish larvae, while several oligopeptides and fatty amides of Symphyonema sp. BACA0090 and Aliinostoc sp. BACA0355 with toxicity. Many clusters associated to the bioactivities remained unidentified, which may represent novel compounds, highlighting the chemodiversity of the BACA culture collection.