Enhancing the production of an antifungal compound from Anabaena laxa through modulation of environmental conditions and its characterization

• Optimization of conditions for bioactive compound production undertaken in Anabaena laxa.
• Highest fungicidal activity under high P, pH of 9, continuous light at stationary phase (28 d).
• TLC, HPLC and FT-IR spectrum analyses revealed cyclic peptide.
• 1H NMR, 13C NMR and GC–MS analyses revealed similarities with majusculamide C from Lyngbya majuscula.
• First report of a fungicidal compound from A. laxa with structural similarity to majusculamide C.

An investigation was undertaken to optimize the physiological conditions and characterize the bioactive compound responsible for fungicidal activity in Anabaena laxa. Fungicidal activity against Pythium debaryanum in the A. laxa cultures increased, when grown under continuous light (CL) at the stationary phase (28 d), with further enhancement on doubling phosphorus levels and high pH (9.0) in the growth medium. Preparatory thin layer chromatography analyses revealed the peptide nature of the fungicidal metabolite, with highest activity in a spot with Rf 0.13. The bioactive fraction (in terms of fungicidal activity) was isolated and identified using HPLC with a retention time of 14.7. Fourier transform infrared (FT-IR) spectrum of the purified bioactive fraction indicated the cyclic peptide nature of the antifungal compound. The structural elucidation using 1H, and 13C NMR analyses revealed the same number and type of carbons as present in previously reported majusculamide C from Lyngbya majuscula. GC–MS indicated a similar major mass ion fragment spectra, with peaks as previously obtained from majusculamide C. This represents a first report on biosynthesis of a fungicidal compound in A. laxa, with structural similarities to majusculamide C.