N-197. Characterization and Classification of Thermophiles from Hot Creek, CA by Molecular Methods

Y-J. Chen1, R. A. Barco2, T. M. Salmassi1;
1California State Univ., Los Angeles, CA, 2Univ. of Southern California, Los Angeles, CA.

Geothermally derived arsenite is rapidly oxidized to arsenate by bacteria at Hot Creek, a geothermally active, arsenic-rich tributary of the Owens River. In the present study, six recently-isolated, arsenite-oxidizing, thermophiles (A11*, 4H(A), 5F(B)*, 5F(B)Fs, 5(F)D, 5H*) from Hot Creek were characterized. Variable temperature experiments suggest that of these 6 isolates, 5 have their optimum growth rate at 65°C with the exception of A11* which has a optimum growth temperature at 62°C. The maximum tolerance concentration (MTC) for arsenite for most isolates is as high as 3.8-4.2 mM or more. Only A11* has a lower MTC for arsenite of about 2.2 mM. Experiments conducted under anaerobic conditions to determine the electron acceptors that could be used by these isolates suggests that all 6 isolates are able to grow using molecular oxygen, arsenate, nitrate, ferric iron, sulfur, sulfate and thiosulfate as electron acceptors. Morphologically, all isolates were gram-negative rods as observed by light microscopy. Finally, the fully-sequenced 16S rRNA genes from the thermophilic isolates suggests that A11* is most closely related to Thermus aquaticus YT-1 with 96% similarity. The remaining 5 isolates group with Thermus sp. T2 with similarities ranging from 96%-97%. Through characterization of these microorganisms, this project contributes to the understanding of the ecological roles of these organisms in this high-temperature, arsenic-rich environment.