a) Real-time PCR standard curves obtained using primer pairs CteA2 (Cte, diamonds) and 341F/534R (Eub, squares) using 10fold serial dilutions of C. testosteroni genomic DNA as template DNA. Linear regressions are calculated using the large dots of each series. Error margins are too small to be visible. b) Abundances of C. testosteroni in the activated sludge inoculum (AS) and the two testosterone enrichment steps (E1 and E2) as measured by real-time PCR and quantitative FISH. nd: not detectable.