POPULATION-DYNAMICS OF PHENOL-DEGRADING BACTERIA IN ACTIVATED-SLUDGE DETERMINED BY GYRB-TARGETED QUANTITATIVE PCR

A method for quantifying bacterial populations introduced into an acti vated-sludge microbial community is described. The method involves ext raction of DNA from activated sludge, appropriate dilution of the extr acted DNA with DNA extracted from nonintroduced activated sludge, PCR amplification of a gyrB gene fragment from the introduced strain with a set of strain-specific primers, and quantification of the electropho resed PCR product by densitometry. The adequacy of the method was exam ined by analyzing the population dynamics of two phenol degrading bact eria, Pseudomonas putida BH and Comamonas sp, strain E6, that had been introduced into phenol-digesting activated sludge. The density of eac h of the two populations determined by the PCR method immediately afte r the introduction was consistent with the density estimated from a pl ate count of the inoculum. This quantitative PCR method revealed diffe rent population dynamics for the two strains in the activated sludge u nder different phenol-loading conditions. The behavior of both of thes e strains in the activated sludge reflected the growth kinetics of the strains determined in laboratory axenic cultures.