Endophytic fungi of marine macroalgae and the bioactive chemicals they produce have not been widely explored or documented. In this study, fungal endophytes were isolated from four species of brown, three species of red, and two species of green marine algae collected from the Shetland Islands, UK. Sixty-four distinct endophytes were isolated, 36 of which were identified to the genus or species level, with the highest diversity of isolable fungi being obtained from the green algae. Extracts of fungal tissue and spent nutrient broth were prepared from each isolate and screened for bioactivity. Antimicrobial and larvicidal assays revealed that the extracts from 24 endophytes showed antifungal activity, 25 displayed activity against Gram-positive bacteria, 20 showed activity against Gram-negative bacteria, and 11 showed larvicidal activity.

As the need for new and more effective antibiotics increases, untapped sources of biodiversity are being explored in an effort to provide lead structures for drug discovery. Endophytic fungi from marine macroalgae have been identified as a potential source of biologically active natural products, although data to support this is limited. To assess the antibiotic potential of temperate macroalgal endophytes we isolated endophytic fungi from algae collected in the Bay of Fundy, Canada and screened fungal extracts for the presence of antimicrobial compounds. A total of 79 endophytes were isolated from 7 species of red, 4 species of brown, and 3 species of green algae. Twenty of the endophytes were identified to the genus or species level, with the remaining isolates designated codes according to their morphology. Bioactivity screening assays performed on extracts of the fermentation broths and mycelia of the isolates revealed that 43 endophytes exhibited antibacterial activity, with 32 displaying antifungal activity. Endophytic fungi from Bay of Fundy macroalgae therefore represent a significant source of antibiotic natural products and warrant further detailed investigation.

ACh -Acetylcholine, an endothelial muscarinic receptor agonist AICAR -5-Aminoimidazole-4-carboxamide ribonucleotide (AICAR), an activator of AMPKinase ALBS-Alternative ligand binding site, distinct from the 'classical' ligand binding pocked situated in the NR4A1 ligand binding domain (LBD). CsnB -Cytosporone B, 3,5-Dihydroxy-2-(1-oxooctyl)-benzeneacetic acid, ethyl ester DMEM -Dulbecco's modified Eagle's minimal essential medium cell culture medium 2fLI-2-furoyl-Leu-Ile-Gly-Arg-Leu-amide, a potent and selective PAR2 agonist LBD-Canonical nuclear hormone receptor 'ligand binding domain' L-NAME -Nω-Nitro-L-arginine methyl ester hydrochloride MMEC -mouse microvascular endothelial cells NO -Nitric Oxide NR4A1/Nr4a1-Human nuclear receptor 4A1(murine gene designated as Nr4a1; formerly designated This article has not been copyedited and formatted. The final version may differ from this version.