Screening of terrestrial and freshwater halotolerant cyanobacteria for antifungal activities

Cyanobacterial cultures tolerating 200 mmol l⁻¹ sodium chloride isolated from terrestrial and freshwater habitats of North Maharashtra region of India were evaluated for antifungal activity. Aqueous, methanol, n-propanol, and petroleum ether extracts of 40 cyanobacterial isolates belonging to nine genera were examined for inhibitory activity against five fungal pathogens. Eighteen isolates belonging to genus Oscillatoria dominated the population of halotolerant cyanobacterial cultures. Four antifungal bioassays viz. double layer agar method, disc diffusion assay, silica gel method, and minimum inhibitory concentration (MIC) were used to screen the cultures for antifungal activity. Among the solvents used, methanol extracts showed 34.9% inhibition followed by n-propanol, petroleum ether, and water exhibiting 30.2%, 18.6% and 16.2% inhibition, respectively. The double agar layer method was found to be a suitable method in preliminary screening for handling large number of cultures without extraction of compounds. However, in later screening experiments, silica gel method was seen to be advantageous over MIC and agar disc diffusion methods.