Inhibition Effect of Rosmarinus officinalis L. Essential Oil on Environmental Sulfate-Reducing Bacteria induced Corrosion

Sulfate-reducing bacteria (SRB)-induced corrosion plays an important role in environmental and technological fields, causing huge economic and ecological damage. This study was carried out to deter¬mine the efficacy of Rosmarinus officinalis oil in controlling metal corrosion. Sludge samples were col¬lected from the sulfurous springs in Heet, Anbar governorate, Iraq, to isolate sulfate-reducing bacteria. The samples were enriched using BmA medium under anaerobic conditions. The isolated SRB strain was sub¬jected to biochemical tests and 16S rRNA gene sequencing and identified as Desulfovibrio desulfuricans. One set of the microcosm was sampled every week and the effects of D. desulfuricans on the metal surface were evaluated, in the presence and absence of the essential oil, by using scanning electron microscope. Minimum Inhibitory Concentration and Minimum Bactericidal Concentration of R. officinalis oil against D. desulfuricans were determined at 20 mg/ml, which was sufficient to kill the bacteria in the enrichment medium. The weight loss of the nails which were incubated in the sediment containing D. desulfuricans and R. officinalis oil was significantly lower than those incubated in the presence of D. desulfuricans alone. Scanning electronic microscopic analysis showed that the oil at 20 mg/ml inhibited the formation of bio¬film on the nail's surface. Heavy metal corrosion, cracking and a thick layer of biofilm was observed on the surface of the nail incubated in the sediment without oil treatment. In contrast, addition of R. officinalis oil to the sediment with D. desulfuricans resulted in a lower rate of corrosion and biofilm layers were thinner.