A nice story based on a screen to identify soil bugs that inhibit Bacillus biofilm formation/sporulation from Elizabeth Shank’s group at UNC:
Interspecies interactions have been described for numerous bacterial systems, leading to the identification of chemical compounds that impact bacterial physiology and differentiation for processes such as biofilm formation. Here we identifed soil microbes that inhibit biofilm formation and sporulation in the common soil bacterium Bacillus subtilis. We did so by creating a reporter strain that fluoresces when the transcription of a biofilm-specific gene is repressed. Using this reporter in a co-culture screen, we identified Pseudomonas putida and Pseudomonas protegens as bacteria that secrete compounds that inhibit biofilm gene expression in B. subtilis. The active compound produced by P. protegens was identified as the antibiotic and antifungal molecule 2,4-diacetylphloroglucinol (DAPG). Colonies of B. subtilis grown adjacent to a DAPG-producing P. protegens strain had altered colony morphologies relative to B. subtilis colonies grown next to a DAPG-null P. protegens strain (phlD). Using a subinhibitory concentration of purified DAPG in a pellicle assay, we saw that biofilm-specific gene transcription was delayed relative to untreated samples. These transcriptional changes also corresponded to phenotypic alterations: both biofilm-biomass and spore formation was reduced in B. subtilis liquid cultures treated with subinhibitory concentrations of DAPG. Our results add DAPG to the growing list of antibiotics that impact bacterial development and physiology at subinhibitory concentrations. These findings also demonstrate the utility of using co-culture as a means to uncover chemically-mediated interspecies interactions between bacteria.