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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.

The predator-prey interaction between Myxococcus xanthus and Escherichia coli is a well known microbial behavior, but has not been systematically investigated at the molecular level. In this study, we used the genetic approach to explore the mechanism underlining this interaction.In chapter I of this thesis, we adapted a genetic screening assay originally developed for studying phage-bacteria interactions to isolate and analyze M. xanthus mutants that are defective in their predatory behavior toward E. coli. Our genome-wide genetic screening in M. xanthus led to the discovery of several molecular components that are involved in the predator-prey interaction. Characterization of these M. xanthus mutants in chapter II demonstrated that genes involved in the biosynthesis of the polyketide antibiotic TA, were transcriptionally up-regulated in the presence of E. coli prey cells. Chapter III is focused on screening for E. coli mutants to further explore the genetic components of E. coli involved in its interaction with M. xanthus during predator-prey interaction. Our study shed light on the mechanism underlying the predator-prey interaction between M. xanthus and E. coli by revealing gene functions in both species that could potentially be involved in this intriguing process. More importantly, we demonstrated that M. xanthus is able to sense the presence of E. coli prey cells through direct cell-cell contact, and respond by up-regulating its antibiotic TA production for prey killing, indicating the predator- prey interaction is a well-regulated biological event.

The predator-prey interaction between Myxococcus xanthus and Escherichia coli is a well known microbial behavior, but has not been systematically investigated at the molecular level. In this study, we used the genetic approach to explore the mechanism underlining this interaction.In chapter I of this thesis, we adapted a genetic screening assay originally developed for studying phage-bacteria interactions to isolate and analyze M. xanthus mutants that are defective in their predatory behavior toward E. coli. Our genome-wide genetic screening in M. xanthus led to the discovery of several molecular components that are involved in the predator-prey interaction. Characterization of these M. xanthus mutants in chapter II demonstrated that genes involved in the biosynthesis of the polyketide antibiotic TA, were transcriptionally up-regulated in the presence of E. coli prey cells. Chapter III is focused on screening for E. coli mutants to further explore the genetic components of E. coli involved in its interaction with M. xanthus during predator-prey interaction. Our study shed light on the mechanism underlying the predator-prey interaction between M. xanthus and E. coli by revealing gene functions in both species that could potentially be involved in this intriguing process. More importantly, we demonstrated that M. xanthus is able to sense the presence of E. coli prey cells through direct cell-cell contact, and respond by up-regulating its antibiotic TA production for prey killing, indicating the predator- prey interaction is a well-regulated biological event.