Genetic transformation of the extreme thermophile Thermus thermophilus and of other Thermus spp.

Genetic transformation of auxotrophs of the extreme thermophile Thermus thermophilus HB27 to prototrophy was obtained at high frequencies of 10(-2) to 10(-1) when proliferating cell populations were exposed to chromosomal DNA from a nutritionally independent wild-type strain. The transformation frequency was proportional to the DNA concentration from 10 pg/ml to 100 ng/ml. T. thermophilus HB27 cells did not require chemical treatment to induce competence, although optimal transformation was obtained by the addition of a divalent cation (Ca2+ or Mg2+). Competence was maintained throughout the growth phase, with the highest transformation frequencies at pH 6 to 9 and at 70 degrees C. T. thermophilus HB27 and four other typical Thermus strains, T. thermophilus HB8, T. flavus AT62, T. caldophilus GK24, and T. aquaticus YT1, were also transformed to streptomycin resistance by DNA from their own spontaneous streptomycin-resistant mutants. A cryptic plasmid, pTT8, from T. thermophilus HB8 was introduced into T. thermophilus HB27 Pro- at a frequency of 10(-2).