Identification and functional assessment of endophytic bacterial diversity in Ageratina adenophora (Sprengel) and their interactions with the host plant

Endophytes mainly present in the tissues of the plants. The effects of endophytes on host physiology and ecology have been relatively well studied in many plants, while the functions of endophytes within invasive plants are few that have been reported. Endophytic bacteria considered mutualistic and mediate nutrients availability to facilitate the growth and competitiveness of the host. The present study aimed to check how alien plant species have positive population growth and to identify the functional gene diversities of endophytic bacteria in the tissues. An alien plant, Ageratina adenophora has been experimentally manipulated in order to investigate the bacterial community structure of endophytes in its roots, stems and leaves. Results indicated that after tetracycline treatment, the heights of A. adenophora plants were significantly reduced. Several changes in the host physiological and biochemical properties were detected, including decreased ferredoxin contents, increased iron and chlorophyll concentrations in the leaves. High-throughput sequencing of the bacterial community 16S rRNA genes indicated that endophytic bacteria in untreated A. adenophora plants were dominated by the phyla Cyanobacteria, Proteobacteria, Firmicutes and Bacteroidetes. After treatment with tetracycline, the overall bacterial diversity decreased. To investigate the links between endophytic bacteria and host growth, six strains of bacteria (Acinetobactor johnsonii, Chryseobacterium arthrosphaerae, Bacillus sp., Arthrobacter nitroguajacolicus, Bacillus cereus and an unidentified bacterium sp.) were isolated from A. adenophora. Three of these isolates produced indole-3-acetic acid, which has been shown to promote the growth of A. adenophora plants. These strains also showed strong nematicidal activities, suggesting their potential roles in aiding host defense mechanisms.