Abstract
Actinomycetes are a phylogenetically diverse bacterial group which are widely distributed across terrestrial and aquatic ecosystems. Within this order, the genus Pseudonocardia and their specialised metabolites have been the focus of previous ecological studies due to their antagonistic interactions with other microorganisms and their mutualistic interactions with insects. However, the chemical ecology of free‐living Pseudonocardia remains understudied. This study applies a multi‐omics approach to investigate the chemical ecology of free‐living actinomycetes from the genus Pseudonocardia . In a comparative genomics analysis, it was observed that the biosynthetic gene cluster family distribution was influenced mainly by phylogenetic distance rather than the geographic or ecological origin of strains. This finding was also observed in the mass spectrometry‐based metabolomic profiles of nine Pseudonocardia species isolated from marine sediments and two terrestrial species. Antagonist interactions between these 11 species were examined, and matrix‐assisted laser desorption/ionisation‐mass spectrometry imaging was used to examine in situ chemical interactions between the Southern Ocean strains and their phylogenetically close relatives. Overall, it was demonstrated that phylogeny was the main predictor of antagonistic interactions among free‐living Pseudonocardia . Moreover, two features at m / z 441.15 and m / z 332.20 were identified as metabolites related to these interspecies interactions.