The fungus-growing termite Macrotermes natalensis harbors bacillaene-producing Bacillus sp. that inhibit potentially antagonistic fungi

The ancient fungus-growing termite (Mactrotermitinae) symbiosis involves the obligate association between a lineage of higher termites and basidiomycete Termitomyces cultivar fungi. Our investigation of the fungus-growing termite Macrotermes natalensis shows that Bacillus strains from M. natalensis colonies produce a single major antibiotic, bacillaene A (1), which selectively inhibits known and putatively antagonistic fungi of Termitomyces . Comparative analyses of the genomes of symbiotic Bacillus strains revealed that they are phylogenetically closely related to Bacillus subtilis , their genomes have high homology with more than 90% of ORFs being 100% identical and the sequence identities across the biosynthetic gene cluster for bacillaene are higher between termite-associated strains than to the cluster previously reported in B. subtilis . Our findings suggest that this lineage of antibiotic-producing Bacillus may be a defensive symbiont involved in the protection of the fungus-growing termite cultivar.