Detection by PCR of phage-related DNA in the supernatant of a syntrophically grown culture of Th. Phaeum and Methanothermobacter thermautotrophicus strain TM . Concentrated phage solution from a culture (SC*) and filter-sterilized culture supernatant (SN) were used. As a control for the 16S rDNA PCR, also DNA of Clostridium pasteurianum (C.p.) was used. A PCR product (arrow) was formed with the phage-specific primer in the supernatant (SN Ph) of the culture and in the concentrated phage solution prepared from the same supernatant (SN* Ph). A weak band is visible also in the Clostridium pasteurianum lane with phage-specific primer.