Analysis of bacterial competition using imaging mass spectrometry

The bacterial order actinomycetales are responsible for the production of 65–70 % of microbially produced specialised metabolites with diverse biological activities, with some actinomycetale strains containing over 30 Biosynthetic Gene Clusters encoding for these metabolites. However, only approximately 10 % of these genes are typically transcribed in a mono-culture setting. Furthermore, it has been observed that microbial interactions may induce these cryptic gene clusters providing an ecological advantage to the producer strains. To understand the chemical exchange between strains isolated from the marine environment, microbial interactions were assessed using 49 actinomycetale strains, two Pseudomonas and one Bacillus strain. In total, 72 tri-cultures (three strains) were analysed resulting in 29 strains that showed an altered phenotypes as a result of the interaction. These were then evaluated in a one-to-one culture (two strains) followed by bioactivity screening. Using this data, nine tri-cultures and 27 one-to-one cultures were evaluated using tandem Mass Spectometry, enabling chemically interesting interactions to be prioritized for Time of Flight Secondary Ionisation Mass Spectometry (ToF-SIMS) analysis. ToF-SIMS enables the spatial distribution of parent ions within a sample, in this case, two bacterial strains interacting in a Petri dish. The results that will be presented demonstrate that microbial interactions induce the production of metabolites and ToF-SIMS represents an exciting strategy to study bacterial chemical ecology.