Antibacterial activities of the extracts of cyanobacteria and green algae isolated from desert soil in Riyadh, Kingdom of Saudi Arabia

In compliance to the recent surveys on algal species and their potentials to produce biologically active compounds, seven algal species belonging to cyanobacteria such as Spirulina platensis, Nostoc linckia, Phormidium autumnale, Tolypothrix distorta and Microcystis aeruginosa and green algae such as Chlorella vulgaris, and Dunaliella salina, were isolated from soil in Riyadh, Saudi Arabia. All algal species were morphologically identified using scanning electron microscopy, in addition to light microscopic analysis. Liquid media BG11 was used for cultivation of algal isolates for four weeks; chlorophylls were estimated in the exponential growth phase after two weeks growth in liquid BG11 medium; in liquid medium after four weeks incubation, maximum growth was recorded for Dunaliella salina and N. linckia using cell mass weight. Extraction of algal species were tested for antibacterial activity using agar well diffusion method against a variety of human pathogenic bacteria such as Salmonella suis ATCC 13076; Pseudomonas aeruginosa ATCC 27583; Escherichia coli ATCC 25922; Staphylococcus aureus ATCC 25923; Bacillus subtilis ATCC 6633; Shigella sonnei ATCC 11060 and one yeast Candida albicans ATCC 10231. The bioactive metabolites from algal species were extracted using three different solvent system as methanol: acetone: diethyl ether (5:2:1), acetone and ethanol. The methanol : acetone : diethyl ether solvent system was the most effective solvent system among the three and showed strong activity against S. sonnei, S. aureus, and B. subtilis. Ethanol extract of P. autumnale showed activity against only C. albicans. Key words : Algae isolation, scanning electron microscope, cyanobacteria, green algae, algal extract, antimicrobial activity, human pathogenic bacteria and yeast.