Root and Cd-exposure interactions shape the bacterial community in rhizosphere of hyperaccumulator Sedum alfredii

Rhizosphere bacteria play important roles in plant tolerance and activation of heavy metals. Understanding the bacterial rhizobiome of hyperaccumulators may contribute to the development of optimized phytoextraction for metal-polluted soils. We used 16S rRNA gene amplicon sequencing to investigate the rhizospheric bacterial communities of the Cd hyperaccumulating ecotype (HE) Sedum alfredii in comparison with its non-hyperaccumulating ecotype (NHE). Both planting of S. alfredii and elevated Cd levels significantly decreased bacterial alpha-diversity and altered bacterial community structure in soils. The HE rhizosphere harbored a unique bacterial community differing from those in is bulk soil and NHE counterparts. Several key taxa from Actinobacteria, Bacteroidetes, and TM7 were expecially abundant in HE rhizospheres under high Cd stress. Streptomyces, affiliated to Actinobacteria, was responsible for the majority of the divergence of bacterial community composition between the HE rhizosphere and other soil samples. The abundance of Streptomyces reached 11.67% in HE rhizosphere under high Cd stress, which was 3.31-16.45 fold higher than its abundance in the other soils. These results suggested that the root of hyperaccumulator S. alfredii and Cd exposure shaped a specialized bacterial community in its rhizosphere during phytoextraction of Cd-contaminated soils, and Cd-resistand bacterial, particularly Streptomyces, may play an important role in metal hyperaccumulation.