The cyclopentane ring of calditol, a characteristic lipid molecule of Sulfolobus, a major thermophilic Archaea, was biosynthesized from glucose directly, and galactose was converted to calditol with a similar extent to glucose. This finding indicates the possibility of the "cyclase" enzyme of the calditol carbocycle and the involvement of catalytic oxidoreduction at the C-4 of glucose with broad specificity.