Abstract Chemical defenses produced by lichens represent a yet underexplored force shaping trophic interactions beyond direct consumer deterrence. In termites, dietary intake of such compounds may extend their effects to gut-associated microbial consortia, with consequences for host physiology and colony performance. However, the extent to which lichen-derived metabolites influence microorganisms in insect hosts remains poorly understood. Here, we investigated the bacteriostatic effects of the lichen-derived phenolic compound atranorin on cultivable gut-associated bacteria of the Neotropical termite Constrictotermes cyphergaster (Termitidae: Nasutitermitinae), a generalist species known to include lichens in its diet. Atranorin is a widespread lichen secondary metabolite with documented antimicrobial activity, making it suitable for evaluating diet–microbiota interactions. Atranorin was extracted and chemically characterized from Parmotrema praesorediosum (Lecanorales: Parmeliaceae), yielding a highly pure compound subsequently used in bioassays. Cultivable bacteria were isolated from the crop and P3 hindgut of workers and soldiers, enabling controlled assays and revealing differences across gut compartments and castes. Antibacterial assays demonstrated that atranorin exerted a dose-dependent bacteriostatic effect across most isolates, significantly reducing bacterial growth even at low concentrations. However, microbial responses were taxon-specific, as Sphingomonas paucimobilis exhibited marked tolerance and proliferation under atranorin exposure. These findings suggest that atranorin can act as a selective chemical agent affecting the growth of cultivable gut-associated bacteria, rather than as a broad-spectrum antimicrobial. By linking a lichen-derived metabolite to differential bacterial responses, this study provides evidence that dietary secondary compounds may act as selective factors shaping host-associated bacteria.
Lacerda et al. (2026) studied this question.