Bacteria on leaf surfaces encounter variable access to nutrients and water. This oligotrophic environment is partly due to cuticular waxes that render the leaf surface hydrophobic. While the alkane hydroxylase gene alkB is widespread in leaf-associated bacteria, its activity is not well defined. Here, we developed a bioreporter in Pseudomonas sp. FF2 (PFF2) to monitor alkB promoter activity in vitro and on Arabidopsis thaliana leaves. Single-cell analysis revealed a highly heterogeneous alkB promoter activity, with a subpopulation exhibiting strong fluorescence, consistent with alkane metabolism bet-hedging. On leaves, the promoter was active over the course of seven days, indicating constant access to alkanes over time. While our results support a potential role of alkB in bacterial adaptation to the phyllosphere, direct evidence of cuticular wax degradation is missing. Thus, future studies should trace the incorporation of plant-derived aliphatic compounds to elucidate the ecological relevance of alkB during leaf colonisation.
