Secondary Metabolites as Mediators of Microbial Interspecies Interactions

Description of Project:

Bacteria and Fungi produce numerous secondary metabolites of interest to us as natural product antibiotics.  While the search for new natural product antibiotics reveals a wealth of novel compounds from an astonishing diversity of microorganisms, only a small fraction of these compounds have been developed into clinically useful therapeutics.  In the environments where producer microbes are found, the function and ecological significance of the majority of these compounds is unknown.  Underlying my research is the basic biological question of what functions these diverse secondary metabolites have in the ecology of microbial communities.

Using genetically tractable soil microorganisms, my approach is to study interactions between neighboring colonies of bacteria.  Instead of growth inhibition as an assay, I screen for phenotypes involving alterations in biofilm morphology and development of soil microorganisms as a measure of the influence that secondary metabolites have on target organisms.  For example, a screen of mutant Bacillussubtilis growing on a lawn of Streptomyces coelicolor revealed that Bacillus inhibits S. coelicolor aerial development and sporulation through the action of a secreted surface-active compound, surfactin.  Upon further investigation, I found that surfactin disrupts the developmental regulation of S.coelicolor’s own surface-active compounds required for aerial growth.  In addition to surfactin, Bacillus subtilis produces other secondary metabolites.  Using genetic screens in the presence of multiple Streptomyces species and Fusariumoxysporum (a fungus) I have uncovered phenotypes for all three of the large non-ribosomal peptide synthesis (NRPS) and polyketide synthesis (PKS) secondary metabolite clusters in the B. subtilis genome, allowing me to study the role of the products in interspecies interactions.  This methodology holds promise for studying the production and function of secondary metabolites previously unknown, produced at levels below biochemical detection or not produced under standard laboratory conditions.

Collaborations:

David Z. Rudner Lab- (http://rudnerlab.med.harvard.edu/)
We collaborate with the Rudner lab, experts in microscopy and biochemistry of sporulating Bacillus subtilis.  As we uncover B. subtilis proteins involved in biofilm formation and production of secondary metabolites, we work with the Rudner lab to ask questions about the synthesis and localization of these proteins.

Christopher T. Walsh Lab- (http://walsh.med.harvard.edu/)
We collaborate with the Walsh lab on the chemistry and synthesis of natural products.  Many of the compounds involved in interspecies interactions of interest to our lab are produced by mechanisms of non-ribosomal peptide synthesis and polyketide synthesis.  We work with the Walsh lab to determine the structure of microbial metabolites and to study the function of proteins involved in the synthesis of these compounds.

Neil Kelleher Lab- (http://kelleher.scs.uiuc.edu/)
The Kelleher lab uses powerful Fourier Transformation Mass Spectrometry (FTMS) to study the synthesis of small molecule natural products.  We work with the Kelleher lab to understand the function of individual protein domains in the synthesis of NRPS and PKS metabolites.

Jon Clardy Lab- (http://clardy.med.harvard.edu/)
The Clardy lab studies the structure and synthesis of bioactive natural products.  We collaborate with the Clardy lab to obtain structural information about metabolites of interest to us that arise from our genetic screens.