Evaluation the Activity of Rosemary (Rosmarinus officinalis L.) Essential Oil Against Some Cyanobacteria

Freshwater resources are threatened by harmful algal blooms (HABs ) internationally. The HABs are sometimes direct result of eutrification status caused by pollution entering water bodies, such as partially treated nutrient-rich effluents discharged in the rivers, in addition to fertilizers and animal wastes. The anti-cyanobacterial activity of Rosmarinus officinalis essential oil on Microcystis aeruginosa and Chroococcus minor was evaluated. The essential oil was extracted by steam distillation method, the yield of extraction was 1 % (v/w),and the concentrations of this oil 0.05, 0.1 and 0.15% were prepared. Results revealed very strong antagonistic effects of the essential oil on M. aeruginosa and C. minor growth rates by measuring the amount of chlorophyll- a of each alga. Generally growth rates of both algae severely decreased as the time and the concentrations of the essential oil increased comparing with the growth rate of control (algae without added essential oil) which exponentially increased along with time. M. aeruginosa was more sensitive to the allelopathic effect of the oil.