Characterization of Novel Rod-Shaped Thermophilic Crenarchaeotes from a Hot Spring in the Philippines
Takashi ITOH*a, Ken-ichiro SUZUKIa, Priscilla C. SANCHEZb, and Takashi NAKASEa
a Japan Collection of Microorganisms, The Institute of Physical and Chemical Research (RIKEN), 2-1 Hirosawa, Wako-shi, Saitama 351-01, Japan
b Institute of Food Science and Technology, College of Agriculture, U. P. Los Banos, College, Laguna, Philippines 4031
Members of the order Thermoproteales are rod-shaped hyperthermophilic crenarchaeotes (optimally grow above 85℃) which are commonly encountered in terrestrial solfataric areas or submarine hydrothermal vents. Until now there are two families and three genera described in this order (i.e. Pyrobaculum, Thermoproteus in the family Thermoproteaceae and Thermofilum in the family Thermofilaceae); however, recent our attempt to expand the members of the rod-shaped crenarchaeotes suggested that there were two additional genera in the family Thermoproteaceae among the isolates from hot spring areas in Japan (1). Furthermore, we have isolated two new rod-shaped thermophilic crenarchaeotes, designated as IC-166 and IC-167, from a hot spring in the Philippines. These two isolates were phylogenetically distinct from the known Thermoproteales species or any isolates from hot springs in Japan on the basis of the partial 16S rDNA sequences. In this study, we have characterized the two isolates for understanding their taxonomic positions.
The two strains IC-166 and IC-167 were isolated from a solfataric area called 'Mud spring' of Mt. Maquiling, Laguna, the Philippines. Cells of the both strains were straight or slightly flexuous rod and occasionally bent, branched or bore spherical materials at the end of the cells. They grew in strictly anaerobic cultures supplemented with yeast extract and sulfur. Optimal growth occurred around 85℃ and at pH 3.5- 4.0. Addition of cell extracts from some archaeal strains or vitamin mixture in the cultures stimulated their growth significantly. The DNA base composition was about 43 mol% G+C. Almost whole sequences of the 16S rDNA of the strain IC-167 was determined and compared with those of the other crenarchaeote members. On this analysis, the strain IC-167 stood a separate lineage within the family Thermoproteaceae showing less than 94% similarities to the other members. The partial 16S rDNA sequences of the strain IC-166 was completely consistent with that of the strain IC-167. Interestingly, the two strains housed two small introns at the same positions of the 16S rDNAs. RAPD analysis implied that the both strains were not identical but closely related to each other. These data suggest the two isolates would represent a new genus in the family Thermoproteaceae.
1. Itoh, T., Suzuki, K., and Nakase, T. (1996) In "Culture Collections to Improve the Quality of Life" (eds. Samson, R. A. et al.) p. 472.
