Identification of a Novel Saxitoxin Analogue, 12β-Deoxygonyautoxin 3, in the Cyanobacterium, Anabaena circinalis (TA04)

Saxitoxin (STX) and its analogues, the potent voltage-gated sodium channel blockers, are biosynthesized by freshwater cyanobacteria and marine dinoflagellates. We previously identified several biosynthetic intermediates in the extract of the cyanobacterium, Anabaena circinalis (TA04), that are primarily produced during the early and middle stages in the biosynthetic pathway to produce STX. These findings allowed us to propose a putative biosynthetic pathway responsible for STX production based on the structures of these intermediates. In the present study, we identified 12β-deoxygonyautoxin 3 (12β-deoxyGTX3), a novel STX analogue produced by A. circinalis (TA04), by comparing the retention time and MS/MS fragmentation pattern with those of synthetic standards using LC–MS. The presence of this compound in A. circinalis (TA04) is consistent with stereoselective enzymatic oxidations at C11 and C12, and 11-O-sulfation, during the late stage of STX biosynthesis, as proposed in previous studies.

Antibacterial Activity of Anabaena circinalis Isolated from Fresh Water

Cultures of the blue green algae (cyanobacteria) Anabaena circinalis were identified and isolated from freshwater and their antimicrobial effect was studied. The extract of A. circinalis was tested to investigate its efficiency against four bacterial strains (Achromobacter xylosoxidans, Staphylococcus aureus, Escherichia coli, Shigella dysenteriae. Antimicrobial test was determined by disk diffusion method. Different concentrations of algal extracts (25, 50, 75 and 100%) were tested. Results showed that the highest level of antimicrobial activity was recorded against S. dysenteriae at 100% concentration followed by 25% extract concentration against the same bacteria. In comparison with two antibiotics Ampicillin (AMP), oxacilina (OXA), AMP was the most effective on S. dysenteriae followed by OXA. S. aureus and E. coli were resistant to both antibiotics while they were sensitive to A. circinalis extracts at even at low concentrations (25% and 50%). Thus the present study revealed that extracts of A. circinalis extract is would be a promising natural source, for novel antibiotics, hence worthy for more investigations.