Microbial population dynamics, as determined by PCR-denaturing gradient gel electrophoresis (DGGE), of 2,3,4,5-tetrachlorobiphenyl (CB)-dechlorinating Palos Vedes (PV) cultures (a) and Hudson River cultures (b). Control cultures contained no added 2,3,4,5-CB but were otherwise incubated in an identical manner to the dechlorinating cultures. For PV cultures (a), the DGGE pattern of control culture was on a separate gel; a reference lane R, which is from PCB-dechlorinating culture (Day 297), illustrates the relative locations of bands. Bands indicated with an arrow (with or without a label) were excised and sequenced.