PCR amplification: The PCR was performed according to MCVEIGH et al., (1996) except that with the annealing temperature of 68 °C. The primers used specifically amplified partiallength 16S rRNA gene from actinomycetes and related genera. Although corresponding regions of published 16S rDNA sequences of Thermoactinomyces strains differed by one or two bases from the one of the primers, these primers were successfully applied without modifications to all Thermoactinomyces strains under study. The primers are as follows: ACT283F (5’-GGGTAGCCGGCCUGAGAGGG) corresponding to E. coli 16S rRNA positions 283 to 302 and ACT1360R (5’-CTGATCTGCGATTACTAGCGACTCC) corresponding to the complement of Escherichia coli 16S rRNA positions 1360 to 1336. For the ATCC strains, 10 PCR reactions were pooled whereas 3 PCR reactions were pooled for the environmental strains. If the gel showed more than one PCR product, the target band (about 1050 base pairs (bp)) was purified using the QIAquick gel extraction kit (Qiagen).