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The role of antagonistic secondary metabolites produced by Pseudomonas protegensin suppression of soil-borne phytopathogens has been clearly documented. However, their contribution to the ability of P. protegensto establish in soil and rhizosphere microbiomes remains less clear. Here, we use a four-species synthetic community (SynCom) in which individual members are sensitive towards key P. protegensantimicrobial metabolites (DAPG, pyoluteorin, and orfamide A) to determine how antibiotic production contributes to P. protegenscommunity invasion and to identify community traits that counteract the antimicrobial effects. We show that P. protegensreadily invades and alters the SynCom composition over time, and that P. protegensestablishment requires production of DAPG and pyoluteorin. An orfamide A-deficient mutant of P. protegensinvades the community as efficiently as wildtype, and both cause similar perturbations to community composition. Here, we identify the microbial interactions underlying the absence of an orfamide A mediated impact on the otherwise antibiotic-sensitive SynCom member, and show that the cyclic lipopeptide is inactivated and degraded by the combined action of Rhodococcus globerulusD757 and Stenotrophomonas indicatrixD763. Altogether, the demonstration that the synthetic community constrains P. protegensinvasion by detoxifying its antibiotics may provide a mechanistic explanation to inconsistencies in biocontrol effectiveness in situ.

Siderophores have long been implicated in sociomicrobiology as determinants of bacterial interrelations. For plant-associated genera, like Bacillusand Pseudomonas, siderophores are well known for their biocontrol functions. Here, we explored the functional role of the Bacillus subtilissiderophore bacillibactin (BB) in an antagonistic interaction with Pseudomonas marginalis. The presence of BB strongly influenced the outcome of the interaction in an iron-dependent manner. The BB producer B. subtilisrestricts colony spreading of P. marginalisby repressing the transcription of histidine kinase-encoding gene gacS, thereby abolishing production of secondary metabolites such as pyoverdine and viscosin. By contrast, lack of BB restricted B. subtiliscolony growth. To explore the specificity of the antagonism, we cocultured B. subtiliswith a collection of fluorescent Pseudomonasspp. and found that the Bacillus–Pseudomonasinteraction is conserved, expanding our understanding of the interplay between two of the most well-studied genera of soil bacteria.