Elicitation mimics the inter-species interactions in nature resulting in complex metabolic responses in interacting microorganisms. In pure culture systems in industry and laboratory, most of these metabolic pathways are not active. We therefore, investigated for the first time in a bioreactor, the effect of introducing a live culture of another species to the Streptomyces coelicolor cultures that produce antibiotics such as undecylprodigiosin and actinorhodin. Recently, undecylprodigiosin has also been attributed with antitumor activities. Pure cultures of S. coelicolor produced higher concentrations of actinorhodin compared with undecylprodigiosin in a defined medium in a 2L bioreactor. Elicitation by live cells of Escherichia coli altered this production pattern such that undecylprodigiosin production was enhanced and actinorhodin repressed. E. coli elicitor with a concentration of 1×107cellsmL−1 was added at 2.5% (v/v) so that it did not overtake the growth of S. coelicolor. Since the timing of elicitation is also important, we tested E. coli addition at the beginning, on the second and the fourth day of the start of S. coelicolor cultivation. Day zero elicitation gave the maximum enhancement of undecylprodigiosin production which was 3.5mgL−1 compared with 0.58mgL−1 in the pure culture.