PhD Defense Carlos Neftaly Lozano Andrade

Soil bacteria are prolific producers of a myriad of biologically active secondary metabolites. These natural products are cornerstone in modern society, since they have been used as therapy against diseases and cancer, food additives, and an alternative for chemical pesticides. Despite the antibiotic and drug-discovery view, microbe-centered approaches have revealed a plethora of functions and roles of secondary metabolites, ranging from the so-evident inhibition of competitors to signaling molecules for coordinated behaviors. However, and besides the growing body of knowledge about secondary metabolites, our understanding of the ecological role of these molecules has just begun to be cracked.

In this thesis, we specifically examined the influence of B. subtilis-produced cyclic lipopeptides during bacterial synthetic community (SynCom) assembly, and simultaneously, explored the impact of LPs on B. subtilis establishment success in both a soil-derived semi-synthetic microbial community and a simplified bacterial synthetic community propagated in artificial soil microcosms.
Using the semi-synthetic bacterial mock community approach, we found that cyclic lipopeptides had slight minor effect on the overall bacterial composition but influenced the abundance of the closely related genera Lysinibacillus and Viridibacillus. Similarly, we employed a four-species synthetic bacterial community propagated in a soil-like matrix as reductionist approach to investigate the role of secondary metabolites in synthetic community assembly and B. subtilis ability to thrive such a well-controlled microenvironment. Under this approach, we found that surfactin production enables B. subtilis establishment within the SynCom. Surprisingly, while neither the wild type nor the lipopeptide non-producer strains had major impact on the SynCom composition over time, the B. subtilis and the SynCom metabolomes were both altered during co-cultivation.

Overall, the work presented in this thesis provides insight into the roles of secondary metabolites produced by B. subtilis, broadening our knowledge of these natural products in an ecological context.