Diversity of Cultivated and Uncultivated Actinobacterial Endophytes in the Stems and Roots of Rice

A dual approach consisting of cultivation and molecular retrieval of actinobacterial 16S rRNA genes was used to characterize the diversity of actinobacterial community inhabiting interior of rice stems and roots. Streptomyces is the most frequently isolated genus from rice stems and roots. Forty-five clones chosen randomly among 250 clones in the 16S rRNA gene clone library from roots were affiliated with nine genera of actinobacteria and uncultured actinobacteria (Mycobacterium, Streptomyces, Micromonospora, Actinoplanes, Frankia, Dactylosporangium, Amycolatopsis, Corynebacterium, Rhodococcus, and uncultured actinobacterium). However, 33 clones from stems were affiliated with four genera and uncultured actinobacteria (Streptomyces, Mycobacterium, Nocardiodies, Janibacter, uncultured earthworm cast bacterium, uncultured earthworm intestine bacterium, and uncultured actinobacterium). Species similar to S. cyaneus were isolated from surface-sterilized roots and stems of rice and detected inside rice roots by culture-independent methods. Species similar to S. caviscabies, S. scabies, and S. turgidiscabies were simultaneously detected from the interior of rice stems by the culture-dependent and culture-independent methods. S. galilaeus was detected from the interior of rice stems and roots. These results indicated that some actinobacterial populations in rice stems were correlated with those in roots. Tian and Cao contributed equally to this work