Somayeh makzum - Extremophiles Lab., Dept. of Microbiology, Faculty of Biology, College of Science, University of Tehran, Tehran, Iran
Mohammad Ali amoozegar - Extremophiles Lab., Dept. of Microbiology, Faculty of Biology, College of Science, University of Tehran, Tehran, Iran
S.M. Mehdi dastgheib - Petroleum biotechnology culture collection, research institute of petroleum industry (RIPI), Tehran,Iran

Today, producing hazardous waste water such asspent caustic and releasing them into the environment is a serious threat to the environment and living organisms. Sulfidic spent caustic usually has pH value over 12, salinity about 5-12 % wt and sulfide concentration exceeding 2-3 %wt. physicochemical remediation methods for these wastes have numbers of disadvantages like high cost and producing secondary compounds and this draw attentions to the biological treatment methods for remediation of sulfidic spent caustic.haloalkaliphile sulfur-oxidizing bacteria (HA-SOB) which canthrive in very harsh condition can be exploited to treat this industrial wastewater. Sampling from Meighan salt wet land in Arak was performed. For isolation of HASOB,we used alkaliphilic sulfur respiring strains medium with sodium thiosulfate as electron and energy source and sodium carbonate/bicarbonate as carbon source. To confirm that the purified isolates are obligate autotrophic bacteria their growth on nutrient agar medium has been surveyed. Amongst all the obligate autotrophic strains 4 strainswere selected for molecular identification and 16S rDNA sequence analysis. After 16S rDNA sequence analysis, strains was shown the closest similarity to the genus Thioalkalivibrio.

HA-SOB, bioremediation, spent caustic