Distinctive phyllosphere bacterial communities in tropical trees

Recent work has suggested that in temperate and subtropical trees, leaf surface bacterial communities are distinctive to each individual tree species, and dominated by Alpha- and Gammaproteobacteria. In order to understand how general this pattern is, we studied the phyllosphere bacterial community on leaves of six species of tropical trees at a rainforest arboretum in Malaysia. This represents the first detailed study of ‘true’ tropical lowland tree phyllosphere communities. Leaf surface DNA was extracted and barcoded pyrosequenced targeting the V1-V3 region of 16S rRNA gene. As was previously found in temperate and subtropical trees, each tree species had a distinctive bacterial community on its leaves, clustering separately from other tree species in an ordination analysis. Bacterial communities in phyllosphere were unique to plant leaves in that few numbers of OTUs (0.5%) co-occurred in surrounding soil environment. A novel and distinctive aspect of tropical phyllosphere communities is that Acidobacteria were one of the most abundant phyla across all samples (on average 17%), a pattern not previously recognized. Sequences belong to Acidobacteria were classified into subgroup 1-6 among known 24 subdivisions, and subgroup 1 (84%) was the most abundant group, followed by subgroup 3 (15%). The high abundance of Acidobacteria on leaves of tropical trees indicates that there is a strong relationship between host plant and Acidobacteria in tropical rain forest, which needs to be investigated further.