This species was originally classified when few Thermoproteale organisms were described and the classification decision did not utilize ribosomal RNA sequence information. Recently, it has been argued on the basis of rRNA sequence analysis and physiology that Thermoproteus neutrophilus should be reclassified within the genus Pyrobaculum (Sako et al., 2001). T. neutrophilus consistently falls within the Pyrobaculum clade in rRNA-based trees while Thermoproteus tenax, the type species of Thermoproteus, consistently falls outside of the Pyrobaculum genus. Additionally, Thermoproteus tenax is an acidophile while T. neutrophilus and all of the described Pyrobaculum species are neutrophiles. On the other hand, like T. tenax, T. neutrophilus has a slightly lower optimal growth temperature than described Pyrobaculum species, 85°C, and is non-motile. Shotgun sequence data (5.3-fold coverage) is available for T. tenax (Siebers et al., 2004) thus comparison of a T. neutrophilus genome sequence with T. tenax and Pyrobaculum data would certainly provide enough evidence to correct the classification of this organism.

All of the described Pyrobaculum species are reported to be motile and to have flagella, including P. aerophilum. However, no homologs of flagella genes (archaeal flagella or otherwise) were found in the P. aerophilum genome (Fitz-Gibbon et al., 2002), leading to the exciting assumption that these organisms have a novel set of proteins for flagella production and assembly. The lack of flagella in T. neutrophilus makes it an important comparative genome to aid in the discovery of this system.

Most of the described Pyrobaculum can use any one of several electron acceptors. In contrast, T. neutrophilus appears to use elemental sulfur as its sole electron acceptor. However, having the genome sequence will be important for identifying candidate genes involved in various modes of respiration. T. neutrophilus has also been implicated in the corrosion of stainless steel vapor ducts of the Tejamaniles geothermal power plant in Michoacan, Mexico (Valdez Salas et al., 2000). In Mexico, 10% of the generated electricity is produced by geothermal power plants. The T. neutrophilus genome will aid in the ongoing study of this costly problem that has hindered use of this clean source of energy.

References

Fitz-Gibbon, S.T., Ladner, H., Kim, U.J., Stetter, K.O., Simon, M.I. and Miller, J.H. (2002). Genome sequence of the hyperthermophilic crenarchaeon Pyrobaculum aerophilum. Proceedings of the National Academy of Sciences USA 99: 984-9.

Sako, Y., Nunoura, T., and Uchida, A. (2001) Pyrobaculum oguniense sp. nov., a novel facultatively aerobic and hyperthermophilic archaeon growing at up to 97 degrees C. Int J Syst Evol Microbiol 51: 303-9.

Siebers, B., Tjaden, B., Michalke, K., Dorr, C., Ahmed, H., Zaparty, M., Gordon, P., Sensen, C.W., Zibat, A., et al. (2004) Reconstruction of the central carbohydrate metabolism of Thermoproteus tenax by use of genomic and biochemical data. Journal of Bacteriology 186: 2179-94.

Valdez Salas, B., Schorr Wiener, M., Rioseco de la Pena, L. and Navarrete Bedolla, M. (2000) Deterioration of materials in geothermal fields in Mexico. Materials and Corrosion 51: 698-704.