A,B: Molecular quantification of dsrAB genes by cPCR. Molecular quantification of the copy number of the dsrAB genes in microbial DNA extracted from an environmental sample. A: 150 fg of competitor sequence carried by pKSAII (pdsr-c) was added to serial dilutions (25–250 fg) of the target sequence carried by pAS44 (pdsr). Similarly, 150 fg of competitor DNA was added to 4 ng of DNA extracted from estuary sediments (dsr-s). The PCR products were analyzed on agarose gel. DNA masses of pAS44: lanes 2, 250 fg; 3, 150 fg; 4, 100 fg; 5, 50 fg; 6, 25 fg, DNA from sediment samples lanes 7–10. Size ladder (Eurogentec), lane 1. B: The relative intensities of the PCR bands were used to construct the corresponding calibration curve log (pdsr/pdsr-c). The dsr-s/pdsr-c ratio was plotted on the curve and the copy number of dsrAB genes amplified from bacterial DNA extracted from environmental sediment was deduced assuming a mass of 7.81×10−18 g for pAS44, which carries a single copy of the target sequence.
