Abstract: | The aim of this study is to characterise the bacterial isolates of Jordanian oil refinery sludge for the purpose of using microorganisms in treating industrial wastewater effluents that contains hydrocarbons. Morphological, physiological, biochemical, antimicrobial susceptibility tests and 16S-23S rRNA spacer region polymorphism were used to characterise the isolated thermotolerant Bacillus, with specific reference to Bacillus strains. Data were coded and analysed by numerical techniques using the Gower coefficients and by average linkage (UPGMA) analysis. The study resulted in allocation of strains into two areas at 50.0% similarity levels and ten major phenons at 78.0% similarity level. Amplification of 16S-32S rRNA genes divided all strains into two areas at 48.0% similarity level; however, at 78.0% similarity level five taxonomically distinct phenons were evident. |