Soil bacterial community structure in five tropical forests in Malaysia and one temperate forest in Japan revealed by pyrosequencing analyses of 16S rRNA gene sequence variation

Bacterial community structure was investigated in five tropical rainforests in Sarawak, Malaysia and one temperate forest in Kyoto, Japan. A hierarchical sampling approach was employed, in which soil samples were collected from five sampling-sites within each forest. Pyrosequencing was performed to analyze a total of 493,790 16S rRNA amplicons. Despite differences in aboveground conditions, the composition of bacterial groups was similar across all sampling-sites and forests, with Acidobacteria, Proteobacteria, Verrucomicrobia, Planctomycetes and Bacteroidetes accounting for 90% of all Phyla detected. At higher taxonomic levels, the same taxa were predominant, although there was significant heterogeneity in relative abundance of specific taxa across sampling-sites within one forest or across different forests. In all forests, the level of bacterial diversity, estimated using the Chao1 index, was on the order of 1,000, suggesting that tropical rainforests did not necessarily have a large soil bacterial diversity. The average number of reads per species (OTUs) per sampling-site was 8.0, and more than 40-50% of species were singletons, indicating that most bacterial species occurred infrequently and that few bacterial species achieved high predominance. Approximately 30% of species were specific to one sampling-site within a forest, and 40-60% of species were uniquely detected in one of the six forests studied here. Only 0.2% of species were detected in all forests, while on average 32.1% of species were detected in all sampling-sites within a forest. The results suggested that bacterial communities adapted to specific micro- and macro-environments, but macro-environmental diversity made a larger contribution to total bacterial diversity in forest soil.