Summary auto-generated
Researchers isolated two novel thermophilic bacterial strains (CB-225 and CB-226T) from hot springs in Taiwan that grow optimally at 50°C. These aerobic, non-motile, yellow-pigmented rods were identified as a new species, Pseudoxanthomonas taiwanensis, within the genus Pseudoxanthomonas. The strains were characterized using morphological observations, biochemical tests, fatty acid analysis, DNA sequencing, and phylogenetic analysis. A notable feature of these organisms is their unusual denitrification capability: they reduce nitrite (but not nitrate) to produce nitrous oxide (N2O) as the sole end product, a process observed rarely in thermophilic bacteria. Unlike the related mesophilic species P. broegbernensis, P. taiwanensis lacks polar flagella and has distinctly different biochemical properties including positive β-glucosidase activity and reduced carbon source utilization. DNA-DNA hybridization studies confirmed the strains represent a single species distinct from existing Pseudoxanthomonas species. The discovery of N2O-producing thermophilic bacteria in geothermal environments expands understanding of nitrogen cycling and potential biological sources of this potent greenhouse gas in extreme environments.
Key findings
- Two thermophilic strains (CB-225 and CB-226T) isolated from Chi-ban Hot Springs represent a new species, Pseudoxanthomonas taiwanensis, confirmed by 16S rDNA sequencing and DNA-DNA hybridization studies.
- P. taiwanensis exhibits truncated denitrification, reducing nitrite to nitrous oxide (N2O) only, without reducing nitrate—a rare characteristic in thermophilic bacteria.
- The novel species differs from the only other Pseudoxanthomonas species (P. broegbernensis) by thermophilicity (50°C optimum versus mesophilic growth), absence of polar flagella, and distinct biochemical properties.
- P. taiwanensis demonstrates higher N2O production at elevated temperatures and microaerobic conditions, potentially reflecting adaptation to geothermal environments with high temperature and limited oxygen.
- The discovery identifies thermophilic bacteria in hot springs as biological sources of N2O emissions, contributing to understanding of the global nitrogen cycle and greenhouse gas sources.
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Abstract
Two novel thermophilic bacterial strains, with an optimum growth temperature of between 50 and 60 degrees C, 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 N(2)O 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)). P. 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.