Endophytic bacterium Buttiauxella sp. SaSR13 improves plant growth and cadmium accumulation of hyperaccumulator Sedum alfredii.

Inoculation with endophytic bacterium has been considered as a prospective application to improve the efficiency of phytoextraction. In this study, the effect of Buttiauxella sp. SaSR13 (SaSR13), a novel endophytic bacterium isolated from the root of hyperaccumulator Sedum alfredii, on plant growth and cadmium (Cd) accumulation in S. alfredii was investigated. Laser scanning confocal microscopic (LSCM) images showed that SaSR13 was mainly colonized in the root elongation and mature zones. The inoculation with SaSR13 to Cd-treated plants significantly enhanced plant growth (by 39 and 42% for shoot and root biomass, respectively), chlorophyll contents (by 38%), and Cd concentration in the shoot and root (by 32 and 22%, respectively). SaSR13 stimulated the development of roots (increased root length, surface area, and root tips number) due to an increase in the indole-3-acid (IAA) concentrations and a decrease in the concentrations of superoxide anion (O2.-) in plants grown under Cd stress. Furthermore, inoculation with SaSR13 enhanced the release of root exudates, especially malic acid and oxalic acid, which might have facilitated the uptake of Cd by S. alfredii. It is suggested that inoculation with endophytic bacterium SaSR13 is a promising bioaugmentation method to enhance the Cd phytoextraction efficiency by S. alfredii.