Succession and phylogenetic composition of eubacterial communities in rice straw during decomposition on the surface of paddy field soil

To estimate the bacterial communities in rice straw left on the soil surface of paddy fields, polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) analysis was conducted. Rice straw samples were placed on the soil surface in a Japanese paddy field under drained conditions after harvest and under flooded conditions after the transplanting of rice. The residual samples on the soil surface under upland conditions were collected just before spring plowing and were replaced again on the soil surface after transplanting, under flooded conditions. The DGGE patterns of the bacterial communities in rice straw on the surface of paddy field soil were divided into three groups, namely rice straw samples before placement, under drained conditions and under flooded conditions. Sequence analysis of DGGE bands indicated that most of the bacterial members in rice straw during decomposition on the soil surface in the paddy field belonged to Gram-negative bacteria. The bands that commonly existed throughout the periods under flooded and upland conditions were closely related to alpha-Proteobacteria. The groups of Spirochaetes and delta-Proteobacteria were often observed during flooded periods, although the members of Bacteroidetes, alpha-Proteobacteria, Gemmatimonadetes and Actinobacteria were also detected under flooded conditions. In contrast, the bands characteristic to the rice straw left on the soil surface of the paddy field under drained conditions belonged to Bacteroidetes and gamma-Proteobacteria. This finding clearly indicates that the bacterial communities responsible for rice straw decomposition were determined by the water regime in the paddy field, and various members of Gram-negative bacteria have contributed to the decomposition of rice straw left on the soil surface in a paddy field.