Antibacterial potential of γ-linolenic acid from Fischerella sp colonizing Neem tree bark

Pharmaceutically important gamma-linolenic acid (GLA) was produced (4.1 mg g(-1) dry wt) by laboratory grown cyanobacterium Fischerella sp. colonizing Neem (Azadirachta indica) tree bark. GLA isolated from the test cyanobacterium was active against Staphylococcus aureus ATCC 25923, Escherichia coli ATCC 25992, Salmonella typhi (local strain), Pseudomonas aeruginosa ATCC 27853 and Enterobacter aerogenes MTCC 2822. The overproduction of GLA was also monitored by altering phosphate and nitrate levels in the nutrient medium. A doubling in phosphate concentration (58 mu M) increased GLA level up to 12% over that of control cells while half of this phosphate level reduced GLA synthesis by 8%. In contrast, elevated nitrate concentrations (5 and 10 mM) stimulated biomass yield but not GLA, as the levels approximated to the nitrate-lacking control. The antibacterial potential of GLA from Fischerella sp. grown at varying P or N levels was at variance as evidenced by the diameter of inhibition zones against S. aureus. This variation in inhibition zones reflected differing levels of GLA as ascertained quantitatively by HPLC.