RESUMEN
Aims: Some of methanotrophic bacteria and nitrous oxide (N2O) reducing bacteria have been proven able to support the plant growth and increase productivity of paddy. However, the effect of application of the methanotrophics and N2O reducing bacteria as a biofertilizer to indigenous nitrogen-fixing bacteria and total bacterial community are still not well known yet. The aim of the study was to analyze the diversity of nitrogen-fixing bacteria and total bacterial communty in lowland paddy soils. Methodology and results: Soil samples were taken from lowland paddy fields in Pelabuhan Ratu, Sukabumi, West Java, Indonesia. There were two treatments applied to the paddy field i.e biofertilizer-treated field (biofertilizer with 50 kg/ha NPK) and control (250 kg/ha NPK fertilizer). There were nine different nifH bands which were successfully sequenced and most of them were identified as unculturable bacteria and three of them were closely related to Sphingomonas sp., Magnetospirillum sp. and Ideonella dechloratans respectively. In addition, there were 20 different 16S rDNA bands which were successfully sequenced. Phylogenetic analysis of the sequence showed that there were 5 phyla of bacteria, i.e. Proteobacteria (Alphaproteobacteria and Gammaproteobacteria), Chlorofexi, Gemmatimonadetes, Clostridia, and Bacteroidetes respectively. Alphaproteobacteria was the most dominant group in lowland paddy field. Microbial diversities in the biofertilizer-treated field were lower than that of 100% fertilizer-treated field either based on nifH and 16S rDNA genes. Conclusion, significance and impact study: Biofertilizer treatment has lower microbial diversity than control, either based on nifH and 16S rDNA genes.