Isolation and characterization of indigenous thermophilic bacteria active in natural attenuation of bio-hazardous petrochemical pollutants

Common petrochemical compounds, such as homocyclic polyaromatic hydrocarbons and heterocyclic NOS-polyaromatics (NOS-compounds), were used as the sole carbon and energy source to enrich indigenous bacteria harboring the catabolic ability to degrade these compounds from petroleum-contaminated soils from Kuwait. Chemical analysis of the extracted soil materials revealed residual amounts of oil (<5% w/w), presumably of heavy oil fractions with elevated S-content. Aerobic culturable mesophilic polyaromatic hydrocarbon- and NOS-degraders were abundant in these soils, whereas their moderately thermophilic counterparts constituted only a minor fraction. Glucose stimulated the growth of mesophiles and drastically suppressed the number of thermophiles. 16S rDNA was amplified by PCR from nine of the purified thermophilic strains, using primers specific for eubacteria. Sequencing of 900 bp of the 16S rDNA and database homology search tentatively aligned these isolates to low G+C Gram positive bacteria of the family Bacillaceae. Electron microscopy characterization revealed endospore-forming bacilli varying in size, with well-structured cell walls. Gas chromatography and mass spectrometry (GC/MS) analysis revealed a versatile catabolic ability of the pure and mixed cultures to degrade all tested compounds. The metabolism of the offered substrates does not involve co-metabolism, since all pure cultures consumed the offered substrates completely.