The diversity of iron reducing bacteria communities in subtropical paddy soils of China

Iron(III) reducing bacteria (FeRB), involved in C and N cycle, are vital to regulating environmental biogeochemical processes. Although many important FeRB have been isolated and identified, the diversity of FeRB communities in paddy soils remains largely unknown. Four soils (rice-rapeseed rotation and rice-fallow/flooded rotation collected from Qianjiang, QR and QF soil, respectively, and rice-rapeseed rotation and rice-fallow/flooded rotation collected from Xianning XR and XF soil, respectively) that varied with respect to crop rotation and soil properties, were used in the current study. Incubation experiments were conducted under flooding at 25 °C for the evaluation of FeRB and Fe2+ production. The diversity of FeRB community in each soil was evaluated. The composition of the FeRB community of each soil (QR, QF, XR and XF soil) was determined using enrichment culturing techniques under anaerobic conditions and high-resolution bar-coded reversible terminators. The dominant groups (≥5% of all sequences) were Proteobacteria and Firmicutes, and some rare phyla were also identified. At the genus level, the dominant composition of the clone libraries suggested that known FeRB genera were well represented (e.g. Brevundimonas, Pseudomonas, Burkholderia, Stenotrophomonas and Sporomusa). The analysis also identified novel enrichment culture bacteria genera, such as Sphingomonas, Pandoraea and Azospira, which might be involved in Fe3+ reduction in paddy soils. The diversity of FeRB communities were greatly affected by crop rotation, as well as soil properties such as parent material, pH and C/N ratio. Additionally, the Fe2+production in four soils were significantly different on 40-day incubation. These results indicate that the variation in soil properties and crop rotation have significant effects on the diversity of FeRB community which regulated soil Fe+3 reducing processes.