General Information: Geobacillus kaustophilus strain HTA426 was first isolated from deep sea sediment of the Mariana Trench in the Pacific Ocean and belongs to a closely related group of thermophilic Bacillus spp. Members of this genus were originally classified as Bacillus. Recent rDNA analysis and DNA-DNA hybridization studies using spore-forming thermophilic subsurface isolates provided enough evidence to define the phylogenetically distinct, physiologically and morphologically consistent taxon Geobacillus. Geobacillus species are chemo-organotrophic, obligately thermophilic, motile, spore-forming, aerobic or facultatively anaerobic. This organism was compared with mesophilic Bacillus spp. to identify genome characteristics and specific genes related to thermophilia. Analysis of the amino acid compositions showed clear differences between Geobacillus kaustophilus and the mesophilic bacilli. In addition, the higher G+C content in Geobacillus kaustophilus rRNA also appears correlated to thermophilia. In addition, tRNA modification by the Geobacillus kaustophilus specific tRNA methyltransferases probably aids in the thermoadaptation of this organism.