Biodegradation and stress in the phyllosphere

In soil, aquatic and marine environments, bacterial degradation of organic pollutants has been well studied. However, via deposition or volatile absorption, these pollutants can also accumulate on plant leaves, where they become accessible for degradation by bacteria that colonise the leaf surface, or phyllosphere. The phyllosphere is an environment that evokes high levels of bacterial stress due to rapid changes in humidity, temperature and solar radiation. In this project, we investigated how bacteria cope with phyllosphere stress in relation to their catabolic activity towards pollutants. For this, we used two different approaches. Firstly, we tested the phyllosphere performance of several model strains with different catabolic capabilities. Of these, only 4-chlorophenol degrading strain Arthrobacter chlorophenolicus A6 exhibited a phyllosphere fitness that was comparable to our control bacterium, leaf coloniser Erwinia herbicola 299R. Secondly, we isolated pollutant-degrading bacteria from two phyllosphere environments: an apple orchard that was treated with the foliar pesticide triadimenol, and a vegetated shoulder along a major Dutch highway. Enrichment cultures were checked for growth on 4-chlorophenol, a degradation product of triadimenol, and toluene, a common traffic-related pollutant. Several 4-chlorophenol degrading strains were recovered from the apple orchard phyllosphere and were all confirmed to belong to the genus Arthrobacter. Toluene degrading phyllosphere bacteria from near the highway were identified as Rhodococcus sp. Phyllosphere fitness and stress resistance were variable between isolates. One of the Arthrobacter strains was an excellent leaf coloniser, superior to A6 and 299R. Ongoing studies are exploiting the available genomic resources for A. chlorophenolicus A6 to obtain a transcriptional profile of this strain under phyllosphere conditions and expose any hardwiring between genes involved in stress resistance and pollutant degradation