Plant Growth Promotion by Endophytic Bacteria Isolated from Rice (Oryza sativa)

Endophytic bacteria are widely studied because of their plant-growth-promoting benefits. One hundred and twenty-six endophytic bacteria were isolated from rice roots and stems in this study. Based on their partial 16S rRNA gene sequences, they were characterized as members of phyla Firmicutes , Proteobacteria , Bacteroidetes and Actinobacteria . Among these, isolates 1017, 1048 and 3037 likely represented novel bacterial species of genera Pedobacter , Sphingomonas and Paenibacillus , respectively, based on their relatively low sequence similarities (<98.5%) with recognized bacterial species. All isolates were tested for their growth promotion in rice seedlings in vitro . The increases of fresh weight ranging from 2.30 to 3.18 fold were observed in rice seedlings that were inoculated with twelve bacterial isolates when compared to the water-treated control group. These isolates were members of genera Bacillus (ten isolates), Micrococcus (one isolate) and Acinetobacter (one isolate). The presence of nifH , siderophore production, indole-3-acetic acid (IAA) synthesis and ACC-deaminase activity were determined in these twelve isolates. The most common characteristic was the nifH gene that was detected in five isolates. The result obtained in our study demonstrated the diversity of endophytic bacteria in rice and their potential application as biofertilizers.