Pristine and oil-contaminated desert soil samples from Kuwait harbored between 10 and 100 cells g(-1) of hydrocarbonoclastic bacteria capable of growth at 50 °C. Enrichment by incubation of moistened soils for 6 months at 50 °C raised those numbers to the magnitude of 10(3) cells g(-1). Most of these organisms were moderately thermophilic and belonged to the genus Bacillus; they grew at 40-50 °C better than at 30 °C. Species belonging to the genera Amycolatopsis, Chelativorans, Isoptericola, Nocardia, Aeribacillus, Aneurinibacillus, Brevibacillus, Geobacillus, Kocuria, Marinobacter and Paenibacillus were also found. This microbial diversity indicates a good potential for hydrocarbon removal in soil at high temperature. Analysis of the same desert soil samples by a culture-independent method (combined, DGGE and 16S rDNA sequencing) revealed dramatically different lists of microorganisms, many of which had been recorded as hydrocarbonoclastic. Many species were more frequent in the oil contaminated than in the pristine soil samples, which may reflect their hydrocarbonoclastic activity in situ. The growth and hydrocarbon consumption potential of all tested isolates were dramatically enhanced by amendment of the cultures with Ca(2+) (up to 2.5 M CaSO4). This enhanced effect was even amplified when in addition 8 % w/v dipicolinic acid was amended. These novel findings are useful in suggesting biotechnologies for waste hydrocarbon remediation at moderately high temperature.