# The Alkane 1‐Monooxygenase Gene alkB of Pseudomonas sp. FF2 Is Upregulated During Colonisation of Arabidopsis thaliana Leaves

## TL;DR

Scientists studied how bacteria adapt to leaf surfaces by monitoring a gene involved in breaking down alkanes, finding varied gene activity that suggests a survival strategy.

## Contribution

A bioreporter was developed to study alkB promoter activity in Pseudomonas sp. FF2 on Arabidopsis leaves, revealing heterogeneous expression patterns.

## Key findings

- AlkB promoter activity in Pseudomonas sp. FF2 was heterogeneous, with some cells showing strong fluorescence.
- Promoter activity was sustained on Arabidopsis leaves for seven days, suggesting ongoing access to alkanes.
- The study supports a potential role for alkB in bacterial adaptation to leaf environments but lacks direct evidence of wax degradation.

## Abstract

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.

Given that leaf cuticular waxes restrict access to nutrients and water to bacteria on leaf surfaces, we developed a bioreporter in Pseudomonas sp. FF2 to monitor the activity of the alkB promoter, involved in alkane degradation. The bioreporter revealed heterogeneous alkB expression in vitro and on
Arabidopsis thaliana
leaves, consistent with a bet‐hedging strategy.