Diversity, heavy-metal tolerance and indoleacetic acid production of bacterial endophytes in Bidens pilosa

Abstract:

[Background] Plants are inhabited by diverse bacterial endophytes that are closely related to the growth and stress tolerance of their hosts. Bidens pilisa L. is a highly invasive plant species with strong stress tolerance. However, up to date, there is limited literature reporting the research involving the bacterial endophytes of the plant species. [objective] To investigate and characterize the diversity of bacterial endophytes community of B. pilisa, and to obtain the bacterial isolates from the plant species with both potential of heavy metal-tolerance and indoleacetic acid (IAA) production. [Methods] The diversity of bacterial endophytes community was analyzed by using MiSeq high-throughput sequencing method. The tolerance ability to heavy metals Pb, Cd, Ni, and Hg, as well as the IAA-producing ability of bacterial endophytes were evaluated by using culture-dependent method. [Results] We recovered a total of 4 031 distinct operational taxonomic units from the total bacterial endophytes community of B. pilosa, which could be affiliated with 25 distinct bacterial phyla, 51 distinct bacterial classes, 76 distinct bacterial orders, 182 distinct bacterial families, and 536 distinct bacterial genera. At the genus level, the most dominant bacterial genera detected from the root, stem, leaf, and seed of B. pilosam were Enterobacter, Acinetobacter, Sphingomonas, and Pseudomonas, respectively, followed by Burkholderia, Methylobacterium, Pseudomonas, and Pantoea. Using culture-dependent method, we obtained 34 bacterial isolates from the internal tissues of B. pilisa and all obtained strains showed the tolerance at least to one tested heavy metal. Seven strains (numbered GF-1, GF-8, YF-1, YF-2, JF-1, GF-2, JF-8, respectively) could produce IAA with IAA yields varying in the ranging from 57.48?312.22 μg/mL. Based on 16S rRNA gene sequence analysis, the 7 IAA-producing strains were identified, and strains GF-1, GF-8, YF-1, YF-2, JF-1 as Bacillus spp., strain GF-2 as Pseudomonas sp., strain JF-8 as Burkholderia sp. [Conclusion] The bacterial endophytes community of B. pilosa has high population diversity. Bacterial endophytes strains GF-1, GF-8, YF-1, YF-2, JF-1, GF-2, and JF-8 obtained from B. pilosa show not only multi-heavy metals tolerance also high IAA production, being good candidates used as bio-inoculation agent for bioremediation of heavy metal-contaminated soil.