Culturable Surface and Endophytic Bacterial Flora of the Maturing Seeds of Rice Plants (Oryza sativa) Cultivated in a Paddy Field

The endophytic bacteria in the seeds of rice plants (Oryza sativa, cultivar Kinuhikari) cultivated on an experimental plot adjacent to a paddy field were studied as the seeds matured by comparing them with the bacteria on the surface of the seeds. Endophytic and surface bacteria were isolated using a nutrient broth and a diluted nutrient broth agar medium. The isolates were identified based on 16S rRNA gene sequences. Three genera (Paenibacillus, Acidovorax and Pantoea) and 2 genera (Stenotrophomonas and Rhizobium) were specific to the inside and to the surface of the seeds, respectively. Six genera (Bacillus, Curtobacterium, Methylobacterium, Sphingomonas, Xanthomonas and Micrococcus) were common to both the inside and the surface. As the seed matured, the flora of culturable endophytic bacteria changed in a different manner from that of culturable surface bacteria. More isolates tolerant of high osmotic pressure were found among the endophytes than among the surface bacteria, especially at the later stages of the maturation process. An increasing number of endophytic isolates exhibited amylase activity at the later stages.