Rubrobacter xylanophilus DSM 9941

Photo: Margaret C. Henk

The first strain of the genus Rubrobacter was isolated from gamma-irradiated hot spring water samples by Yoshinaka (1973). This organism was found to be extremely gamma-radiation resistant, with a higher shoulder dose than the canonical radiation resistant species of the genus Deinococcus. The organism stained Gram-positive and was slightly thermophilic with an optimum growth temperature of about 45ÅC.This strain was originally named Arthrobacter radiotolerans. The phylogenetic relationship of this organism was later clarified by 16S rRNA gene sequence analysis and the organism was transferred to a new genus with the name Rubrobacter (Suzuki et al., 1988). Several years later a single strain isolated from a hot runoff of a carpet factory in the United Kingdom was identified as a new species of the genus Rubrobacter and was named R. xylanophilus (Carreto et al., 1996). This organism, however, had an optimum growth temperature of about 60ÅC, and was a true thermophile. At that time only one strain of each species was known but, soon afterwards a large number of isolates of R. radiotolerans and R. xylanophilus were recovered, after gamma-irradiation of the samples from hot spring water in São Pedro do Sul in Central Portugal (Ferreira et al., 1999). The two species of the genus Rubrobacter represent the oldest lineage (deepest branch) of the Actinobacteria (High G+C Gram-positive bacteria) and are distantly related to several bacteria of medical importance, namely the species of Mycobacterium and the important antibiotic producers of the order Streptomycetales. Some strains of R. xylanophilus are capable of degrading hemicellulose and xylan, and could play a significant role in the environmental degradation of this material.

Even though the species of Rubrobacter have only been isolated from thermal environments, it is unlikely that they are restricted to these environments. It is now known that the DNA of species of Rubrobacter (along with species of Deinococcus) is frequently cloned from desert soils where these organisms may be very abundant. These organisms could, therefore, survive for long periods of time in desert soils, and grow during sporadic rainy periods. Very little research has been done on these organisms and little is known other than their taxonomic characterization.

Carreto L, Moore E, Nobre MF, Wait R, Riley PW, Sharp RJ, da Costa MS (1996) Rubrobacter xylanophilus sp. nov., a new thermophilic species isolated from a thermally polluted effluent. Int. J. Syst. Bacteriol. 46:460-465.
Suzuki K, Collins MD, Iijima E, Komagata K (1988) Chemotaxonomic characterization of a radiotolerant bacterium, Arthrobacter radiotolerans: description of Rubrobacter radiotolerans gen. nov., comb. nov. FEMS Microbiol. Lett. 52:33-40.
Yoshinaka T, Yano K, Yamaguchi H (1973) Isolation of a highly radioresistant bacterium, Arthrobacter radiotolerans nov. sp. Agric. Biol. Chem. 37:2269-2275.
Ferreira AC, Nobre MF, Moore E, Rainey FA, Battista JR, da Costa MS (1999) Characterization and Radiation Resistance of New Isolates of Rubrobacter radiotolerans and Rubrobacter xylanophilus. Extremophiles 3: 235-238.