Molecular Signaling and Regulation of Secondary Metabolites in Actinobacteria

Our group isolated Streptomyces sp. strain rbeES331 from the rhizosphere of the desert plant Solanum hindsianum. Genomic analysis reveals that this strain possesses over 20 biosynthetic gene clusters (BGCs), indicating a significant, yet largely cryptic, potential for producing bioactive secondary metabolites. Our current research aims to decipher the specific regulatory networks required to activate these gene clusters.

We have characterized the strain's ability to inhibit fungal growth, discovering that this bioactivity is strictly regulated by environmental and biotic cues. We found that distinct culture conditions modulate its inhibitory spectrum. Specifically, exposure to chemical signals from the phytopathogen Lasiodiplodia brasilense—as well as specific temperature conditions—significantly enhances the production of antifungal compounds. This suggests the bacterium possesses an adaptive "on/off" mechanism to deploy its defensive arsenal only when specific threats are detected.

In contrast, interactions with Fusarium oxysporum reveal a more complex and critical phenomenon. While Fusarium extracts appear to suppress the bacterium's antifungal activity in vitro, the interaction in planta triggers a drastic response. Although inoculation with Streptomyces or Fusarium individually allows plant survival, their co-inoculation results in a lethal synergy, causing over 70% mortality in tomato plants within 24 hours and severe root malformations in survivors. We are currently utilizing transcriptomics and metabolomics to identify the molecular signals driving this lethal cross-talk and to understand how different fungal metabolites differentially regulate the bacterium's bioactive production.