This study provides a novel attempt to put forward, in De Wit's replacement experiments and game theory, interspecific competition in bioaugmentation using constructed mixed-consortia for species growth and biodecolorization. Previous studies stated that species interactions towards mutualism in mixed cultures were vital to determine optimal decolorization in bioaugmentation. In this study, using De Wit's indices trajectories of relative yields over time disclosed interspecific competition of the model binary-biosystems in various dye-free and dye-bearing cultures. In aerobic growth conditions, Escherichia coli DH5 alpha owned a growth advantage to out-compete Pseudomonas luteola due to preferential growth rate of DH5 alpha. However, in static-decolorization conditions DH5 alpha surrendered proportion of its advantage to enhance color removal of R luteola for total coexistence. Game theory also indicated that there were two Nash equilibria (i.e., total conflict and total cooperation situations) present in the model biosystems. In aerobic growth, DH5 alpha had its growth advantage to exclude P. luteola for dominance (i.e., conflict strategy) according to competitive exclusion principle. In static-decolorization conditions, as the removal of a common dye threat was crucial to both species for survival, both species selected cooperation strategy through metabolite stimulation of DH5 alpha to enhance effective decolorization of P. luteola for long-term sustainable management. (C) 2007 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.