PCR-DGGE analysis followed by sequencing of 16S rDNA was applied to reveal the succession and the phylogenetic composition of the bacterial communities responsible for the composting process of rice straw (RS). RS under the composting process exhibited more complex DGGE band patterns with more numerous bands and more diversification in intensity than the initial RS materials. The DGGE patterns of the bacterial communities in the initial RS materials and RS under the composting process were statistically divided into four groups, namely those characterizing the communities associated with the pre-composting stage, and thermophilic, middle, and curing stages of the compost, which corresponded exactly to the same grouping obtained from the PLFA pattern analysis for the same samples (Cahyani et al. 2002: Soil Sci. Plant Nutr., 48, 735-743). Different bacterial members characterized the respective stages as follows: a-Proteobacteria for the initial RS materials, thermophilic Bacillus spp. and actinomycetes at the thermophilic stage, and Cytophaga and clostridial members at the middle and curing stages, respectively. In addition, mesophilic Bacillus members were always present throughout the composting process. Temperature and substrates available to bacteria seemed mainly to determine the composition of the bacterial members at the respective stages.

No abstract

No abstract

The phylogenetic positions of bacterial communities in manganese (Mn) nodules from subsoils of two Japanese rice fields were estimated using polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) analysis followed by sequencing of 16S rDNA. The DGGE band patterns and sequencing analysis of characteristic DGGE bands revealed that the bacterial communities in Mn nodules were markedly different from those in the plow layer and subsoils. Three out of four common bands found in Mn nodules from two sites corresponded to Deltaproteobacteria and were characterized as sulfate-reducing and iron-reducing bacteria. The other DGGE bands of Mn nodules corresponded to sulfate and iron reducers (Deltaproteobacteria), methane-oxidizing bacteria (Gamma and Alphaproteobacteria), nitrite-oxidizing bacteria (Nitrospirae) and Actinobacteria. In addition, some DGGE bands of Mn nodules showed no clear affiliation to any known bacteria. The present study indicates that members involved in the reduction of Mn nodules dominate the bacterial communities in Mn nodules in rice field subsoils.