Dye concentrations were measured at their maximum
absorbance spectra (lmax/520 nm for DB 38 and
lmax/497 nm for CR) in a spectrophotometer, Optima
Photomech 301-D UV/VIS. Absorbance values were
calculated by subtracting the absorbance values of dyefree
control medium from the absorbance values of
synthetic media containing dye. The concentrations of
the dyes were calculated from the calibration curves of
absorbances versus concentrations. Since the metabolites
released from the breakdown products of DB 38
and CR dyes are colourless and the absorbance of
anaerobic metabolites in control was subtracted, the
interference of anaerobic extracellular products to the
absorbance was neglected