Isolation, identification, screening of toxicity and oligopeptides of some marine and brackish cyanobacteria from Norwegian and Pakistani waters, in the search for bioactive natural compounds

Abstract

Cyanobacteria produce a number of bioactive compounds, most of them are oligopeptides. Almost all are known from freshwater species. The aim of this study was to search for marine and brackish water species producing bioactive compounds. To reach this goal, new strains were isolated from Norwegian and Pakistani coastal waters. These and additional strains from NIVA, UiO and UiB culture collections (24 in total), belonging to Chroococcales and Oscillatoriales, were identified based on morphology and sequencing of the partial cpcBA phycocyanin DNA and partial 16S rDNA-regions. Their systematic position was determined by phylogenetic analyses. The bioactivity was tested by Artemia (brine shrimp) bioassay, and the presence of potentially bioactive oligopeptides was determined by LC-MS/MS. All sequences in this study, except of one strain, clustered with known sequences of Geitlerinema spp., Phormidium spp., Pseudoanabaena spp. and Synechococcus spp. with high support. Oscillatoria sp. UIO 017, did however not cluster with any sequence in gene databases. Genetic analyses showed that strains from Norway of the genus Synechococcus divided into 3 clades, suggesting cryptic species. Only one strain, Geitlerinema sp. UK-G-106 was lethal to Artemia nauplii. The combined concentrations of crude extract of Geitlerinema sp. UK-G-106 showed LC50-24 h 0.0032 mg dw mL-1 and was more toxic than toxic freshwater strains Planktothrix rubescens (LC50-24 h 0.05 mg dw mL-1), P. agardhii (LC50-24 h 0.06 mg dw mL-1) and Microcystis aeruginosa (LC50-24 h 0.12 mg dw mL-1). The fractionation of solid phase extractions (methanol:water) of crude extract of Geitlerinema sp. UK-G-106 revealed that the percentage of mortality decreased as concentration of methanol increased. The highest LC50-24 h 0.15 mg dw mL-1 was found at 0% MeOH. LC-MS/MS analysis of Geitlerinema sp. UK-G-106 showed the presence of unknown oligopeptides. These compounds may be screened for additional bioactivity in the search for new therapeutical drugs.