Aims: Nutrient-limited atrazine catabolism study in continuous cultures with biomass retention to mimic in situ environmental conditions and thus gain insight of the efficacy of biosupplementation/biostimulation to eliminate reduced herbicide bioavailability. Methods and Results: Carbon- and nitrogen-limited retentostat (1 and 5 l) cultivation of a combined atrazine (100 mg l\1)-catabolizing association KRA30 was made. As a nitrogen source, through citrate supplementation, increased herbicide catabolism resulted and was complete in the absence of NH4-N. Co-metabolism of the molecule in the presence of succinate was identified. Population characterization by polymerase chain reaction\denaturing gradient gel electrophoresis (PCR\DGGE) indicated component species numerical dominance shifts in response to changes in nutrient limitation, mineral salts composition and biofilm formation, although the total species complement and catabolic potential were retained. Conclusions: Biomass and catabolic capacity maintenance, through cost-effective biosupplementation/biostimulation, should promote atrazine bioavailability and so ensure successful amelioration. Significance and Impact of the Study: All planning, implementation and monitoring of bioremediation programmes should be underpinned by a combination of molecular and (continuous) culture-based methods.