Identification of isoprene-degrading bacteria in phyllosphere and soil communities from high isoprene-emitting oil palm trees by DNA-stable isotope probing

Isoprene is the most abundant biogenic volatile organic compound (BVOC) on Earth, with annual global emissions almost equal to those from methane. Due to its volatile nature and high reactivity, isoprene plays a complex role in atmospheric chemistry and hence, climate. However, very little is known about its biological degradation in the environment. The vast majority of isoprene (500 Tg ·y-1) is produced by terrestrial plants and oil palm is considered one of the highest isoprene-producing trees, with estimated emissions of 175 μg·g-1 dry leaves ·h-1. Oil palm is also a heavily cultivated crop since it is the source of 30% of the vegetable oil in the world and in countries such as Malaysia represents >85% of total agricultural land. The vast expansion of a single crop that emits such high amounts of isoprene have raised serious concerns about its impact on air quality and climate change. We performed DNA Stable Isotope Probing (DNA-SIP) to study the isoprene-degrading community of oil palm trees in a Malaysian plantation and identified novel genera of isoprene-utilising bacteria in both oil palm soils and leaves. isoA amplicon sequencing data also confirmed that oil palm trees harbour a novel diversity of isoA genes, which encode the alpha subunit of the isoprene monooxygenase, a key enzyme in isoprene metabolism. In addition, metagenome assembled genomes (MAGs) were reconstructed from metagenomes from oil palm soil and leaf incubations and analysed to identify isoprene degradation gene clusters in these microorganisms. Finally, analysis of unenriched metagenomes showed that isoA-containing bacteria are more abundant in soils than in the oil palm phyllosphere.