3 The Family Acidothermaceae

Family Acidothermaceae, within the order Actinomycetales, contains thermophilic bacteria isolated from thermal springs and placed in genus Acidothermus. Genus Acidothermus was found and isolatedfromYellowstone National Park, Wyoming, USA,in the course of a search for thermostable cellulases (Mohagheghi et al. Int J Syst Bacteriol 36:435‐443, 1986). Acidothermus cellulolyticus is presently the sole species, in the sole genus of the family Acidothermaceae. A 16S rRNA-based phylogenetic study has found Acidothermus to be most closely related to Frankia; however, other genes have yielded different topologies. The genome of A. cellulolyticus strain 11B has been sequenced recently. Several genes for plant biomass degradation have been characterized; the thermostable properties of A. cellulolyticus enzymes for both cellulose and hemicellulose degradation have value for biotechnological applications. The family Acidothermaceae was initially described as phylogenetically close to Frankia (Frankiaceae), Cryptosporangium (Cryptosporangiaceae), Geodermatophilaceae, (Geodermatophilaceae), Nakamurella (Nakamurellaceae), and Sporichthya (Sporichthyaceae) and grouped into suborder Frankineae. However, this suborder is now an order, Frankiales, and now considered to contain six families: besides the Frankiaceae the Acidothermaceae, the Cryptosporangiaceae, the Geodermatophilaceae, the Nakamurellaceae, and the Sporichthyaceae (Normand P et al. 2012).