Wallace, M.; Allen, M. L.; Karasov, T. L.; Puri, A. W.

In the plant phyllosphere, many bacteria produce pigments to mitigate oxidative stress, including pink-pigmented facultative methylotrophs (PPFMs). PPFMs are prominent members of the phyllosphere microbiota, yet their secondary metabolism remains underexplored. This limits our understanding of how these bacteria interact with other phyllosphere constituents at the molecular level. Here, we develop a screen for PPFM biosynthetic gene clusters and identify listianol, a previously undescribed metabolite that inhibits the pigmentation and growth of diverse bacteria. Listianol blocks carotenoid biosynthesis by targeting the desaturases CrtN and CrtI, revealing a previously unrecognized inhibitory mechanism for a secondary metabolite. This activity sensitizes normally pigmented bacteria to UVB radiation in vitro, and a listianol-producing strain reshapes the composition of a synthetic bacterial community on Arabidopsis thaliana under UVB exposure. Together, these findings establish a platform for exploring PPFM biosynthetic potential and uncover a new metabolite with potential to impact the phyllosphere microbiota composition.