Pseudoxanthomonas taiwanensis sp nov., a novel thermophilic, N2O-producing species isolated from hot springs

Two novel thermophilic bacterial strains, with an optimum growth temperature of between 50 and 60 degreesC, were isolated from the Chi-ban Hot Springs in eastern Taiwan. Strains CB-225 and CB-226(T) were aerobic, thermophilic, non-sporulating, yellow-pigmented heterotrophic organisms. These strains exhibited an unusual denitrification reaction, reducing nitrite, but not nitrate, with the production of N2O only. On the basis of a phylogenetic analysis of 16S rDNA sequences, DNA-DNA similarity data, morphological, physiological and biochemical characteristics, and fatty acid compositions, it was found that the novel strains belonged to the genus Pseudoxanthomonas and represented a novel species within this genus, for which the name Pseudoxanthomonas taiwanensis is proposed; the type strain is CB-226(T) (= ATCC BAA-404(T) = CCRC 17172(T)). A taiwanensis differs from the only member of the genus Pseudoxanthomonas, the mesophilic species Pseudoxanthomonas broegbernensis, in that it exhibits a higher growth temperature and different morphological characteristics, such as the absence of polar flagella.