Bacterial community diversity in the rhizosphere of nickel hyperaccumulator species of Halmahera Island (Indonesia)

Ultramafic soils cover large areas in Indonesia, with over 8000 km2 on Halmahera Island. Nickel hyperaccumulator plants have evolved on these soils which are suspected to host highly nickel tolerant bacteria in their rhizosphere. To date, research has been limited on the characterization of the genetic diversity of such bacterial communities. The objective of this study was to investigate the genetic diversity of bacterial communities in the rhizosphere of nickel hyperaccumulator plants from Halmahera Island to improve knowledge on the factors that drive bacterial community diversity. We collected 45 rhizosphere soils from 10 woody nickel hyperaccumulator species at 16 sites to highlight the influence of plants, soil chemical parameters and site effects on bacterial diversity, richness and composition. A total of 2,508,874 bacterial 16S rRNA gene sequences were obtained and clustered into 6645 OTUs. In total, 40 phyla were identified with the most dominant phyla being Proteobacteria, Acidobacteria, Actinobacteria and Chloroflexi. Redundancy analysis between soil chemical characteristics and bacterial phyla relative abundances for the three main species (Rinorea aff. bengalensis, Ficus trachypison and Trichospermum morotaiense) showed that the main factor driving the bacterial diversity in the rhizosphere of Rinorea aff. bengalensis appears to be the plant itself (regardless of the characteristics of the soil), while the impact of soil conditions was important for the two other hyperaccumulator species. This may be explained by the fact that Rinorea aff. bengalensis (at least in Halmahera Island) is an obligate nickel hyperaccumulator