Identification and colonization of an antagonistic endophytic Burkholderia cepacia Lu10-1 isolated from mulberry

Abstract:

[Objective] To identify and colonize an antagonistic bacterium, Lu10-1, isolated from the healthy mulberry.[Methods] Strain Lu10-1 was identified based on the analysis of its 16S rRNA gene sequence homology, the physiological and biochemical characteristics, and the recA gene sequence comparison. A spontaneous Lu10-1 mutant tolerant to rifampicin and ampicillin were isolated by gradually increasing the concentration of the two antibiotics. The mutants were used to assess the ability of Lu10-1 to colonize mulberry by different inoculation approaches, including stem and leaf acupuncturing, seed soaking, root soaking and leaf daubing. [Results] Lu10-1 belonged to Burkholderia. In the phylogenetic tree, Lu10-1 was the closest relative to B. cepacia (X80284) with more than 98% sequences similarity. The 16S rDNA sequences of Lu10-1 have been registered at GenBank database under the accession number EF546394. Moreover, our results also indicated that the population of strain Lu10-1 living in the mulberry tissues decreased as a whole after the treatment of seed soaking . The bacterial density inside the mulberry seedling tissues decreased to a steady level 20 days after germination. The population of strain Lu10-1 in mulberry leaves and stems after the treatment of root soaking increased first and then decreased. [Conclusion] The strain Lu10-1 fell into Burkholderia cepacia genomovarⅠas a single species. Furthermore, the strain Lu10-1 could colonize and transmit in mulberry, while its resistance to plant pathogen was not changed during the process of colonization compared to the original strains. Taken together, we suggest that Burkholderia. cepacia Lu10-1 will play an important role in the biological control of mulberry disease.

Key words:mulberry; endophytic bacteria; Burkholderia cepacia; identification; colonization