Abstract
The present study focused on the characterization of 10 Curtobacterium citreum strains isolated from the rhizosphere of pioneer plants growing on ultramafic soils from New Caledonia. Taxonomic status was investigated using a polyphasic approach. Three strains (BE, BB, and AM) were selected in terms of multiple-metal resistance and plant-growth-promoting traits. They were tested on sorghum growing on ultramafic soil and compared with the reference strain C. citreum DSM20528 T . To better understand the bacterial mechanisms involved, biosorption, bioaccumulation, and biofilm formation were investigated for the representative strain of the ultramafic cluster (strain BE) versus C. citreum DSM20528 T . The polyphasic approach confirmed that all native isolates belong to the same cluster and are C. citreum. The inoculation of sorghum with strains BE and BB significantly reduced Ni content in shoots compared with inoculation with C. citreum DSM20528 T and control values. This result was related to the higher Ni tolerance of the ultramafic strains compared with C. citreum DSM20528 T . Ni biosorption and bioaccumulation showed that BE exhibited a lower Ni content, which is explained by the ability of this strain to produce exopolysaccharides involved in Ni chelation. We suggested that ultramafic C. citreum strains are more adapted to this substrate than is C. citreum DSM20528 T , and their features allow them to enhance plant metal tolerance.