Imaging Mass Spectrometry Reveals Highly Specific Interactions between Actinomycetes To Activate Specialized Metabolic Gene Clusters

The genomes of actinomycetes contain numerous gene clusters potentially able to encode the production of many antibiotics and other specialized metabolites that are not expressed during growth under typical laboratory conditions. Undoubtedly, this reflects the soil habitat of these organisms, which is highly complex physically, chemically, and biotically; the majority of the compounds that make up the specialized metabolome are therefore adaptive only under specific conditions. While there have been numerous previous reports of waking up the sleeping gene clusters, many involving genetic interventions or nutritional challenges, the role of competing microorganisms has been comparatively little studied. Now, Traxler et al. [M. F. Traxler, J. D. Watrous, T. Alexandrov, P. C. Dorrestein, and R. Kolter, mBio 4(4): e00459-13, 2013, doi:10.1128/ mBio.00459-13] have used the recently described technique of microscale imaging mass spectrometry to analyze in detail the stimulation of specialized metabolite production by the model actinomycete Streptomyces coelicolor A3(2) by growth in proximity to other actinomycetes. The striking finding from these experiments was that growth of S. coelicolor close to each of the five other actinomycetes studied caused it to produce many specialized metabolites that were not made when it was grown in isolation and that the majority of the compounds were interaction specific, i.e., they occurred only in one of the five pairwise combinations, emphasizing the highly specific nature of the interactions. These observations contribute substantially to the increasing awareness of communication between microorganisms in complex natural communities, as well as auguring well for the discovery of useful specialized metabolites based on microbial interactions.