Abstract
Bacteria and fungi in shared environments compete with one another for common substrates, and this competition typically involves microbially-produced small molecules. An investigation of one shared environmental niche, the carton material of the Formosan subterranean termite Coptotermes formosanus, identified the participants on one of these molecular exchanges. Molecular characterization of several termite-associated actinobacteria strains identified eleven known antimicrobial metabolites that may aid in protecting the C. formosanus colony from pathogenic fungal infections. One particular actinobacterial-derived small molecule, bafilomycin C1, elicited a strong chemical response from Trichoderma harzianum, a common soil saprophyte. Upon purification and structure elucidation, three major fungal metabolites were identified, t22-azaphilone, cryptenol, and homodimericin A. Both t22-azaphilone and homodimericin A are strongly upregulated, 123- and 38-fold, respectively, when exposed to bafilomycin C1, suggesting each play a role in defending T. harzianum from the toxic effect of bafilomycin C1.
Highlights
Throughout their evolutionary history insects have engaged in mutually beneficial associations with microbes, including bacteria belonging to the chemically rich class of actinobacteria (Kaltenpoth 2009; Caldera et al 2009; Crawford and Clardy 2011; Nett et al 2009)
Identification of Antimicrobial Agents Produced by Termite-Associated Actinobacteria Nine termite-associated actinobacterial strains – 7 Streptomyces and 2 Kitasatospora strains (Table 1) – were chosen for chemical investigations based on their antimicrobial activity, previously reported in Chouvenc et al (2013b)
Induction and Identification of Antibacterial Metabolites Produced by T. harzianum WC13 One interesting binary competition assay revealed a chemical interaction between Streptomyces sp. 4231 and T. harzianum WC13, where a small molecule produced and excreted by the bacteria changed the growth morphology and upregulated the production of pigments in the fungus (Fig. 2)
Summary
Throughout their evolutionary history insects have engaged in mutually beneficial associations with microbes, including bacteria belonging to the chemically rich class of actinobacteria (Kaltenpoth 2009; Caldera et al 2009; Crawford and Clardy 2011; Nett et al 2009). Previous reports have illustrated the ability of actinobacteria associated with a variety of insects – beetles, ants, termites, and beewolf wasps – to protect the insect hosts from infections by ecologically relevant pathogens (Scott et al 2008; Oh et al 2009a, 2009b; Carr et al 2012; Kaltenpoth et al 2005; Kroiss et al 2010). Due to the sheer size of these nests, they can be difficult to control via conventional soil insecticide treatments (Su and Scheffrahn 1998) and biological control attempts failed to eliminate field colonies
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