The co-culturing of microorganisms is a well-known strategy to study microbial interactions in the laboratory. This approach facilitates the identification of new signals and molecules produced by one species that affects other species’ behavior. In this work, we have studied the effects of the interaction of nine Streptomyces species (S. albidoflavus, S. ambofaciens, S. argillaceus, S. griseus, S. lividans, S. olivaceus, S. parvulus, S. peucetius, and S. rochei) with the predator bacteria Myxococcus xanthus, five of which (S. albidoflavus, S. griseus, S. lividans, S. olivaceus, and S. argillaceus) induce mound formation of M. xanthus on complex media (Casitone Yeast extract (CYE) and Casitone tris (CTT); media on which M. xanthus does not form these aggregates under normal culture conditions. An in-depth study on S. griseus–M. xanthus interactions (the Streptomyces strain producing the strongest effect) has allowed the identification of two siderophores produced by S. griseus, demethylenenocardamine and nocardamine, responsible for this grouping effect over M. xanthus. Experiments using pure commercial nocardamine and different concentrations of FeSO4 show that iron depletion is responsible for the behavior of M. xanthus. Additionally, it was found that molecules, smaller than 3 kDa, produced by S. peucetius can induce the production of DK-xanthenes by M. xanthus.