Unveiling Plant Growth-Promoting Rhizobacteria (PGPR) from Emblica rufuschaneyi , a Ni hyperaccumulator native to Sabah, Malaysia

Emblica rufuschaneyi (Phyllanthaceae) is a nickel (Ni) hyperaccumulator from Sabah, with a high potential for agromining due to its ability to accumulate over 1% Ni in its leaves. Since plant development is a crucial factor in optimising agromining efficiency, strategies to enhance plant growth in metal-rich environments are necessary. Plant growth-promoting rhizobacteria (PGPR) offer a biological approach to enhance plant growth and metal uptake due to their positive effects on plant fitness. This study aimed to isolate and identify potential PGPR associated with E. rufuschaneyi that can help with enhancing the growth of this metal crop. A total of 44 Ni-tolerant bacterial isolates were obtained, with filamentous forms being the most common cell shapes, followed by cocci and bacilli shape. These bacterial isolates were tested for their tolerance toward Ni by culturing them with different concentrations of NiCl 2 and for plant growth-promoting (PGP) traits, which include phosphate solubilisation, and production of siderophores, ammonia, and indole-3-acetic acid (IAA). Most of the isolates exhibited multiple PGP traits, and 13.6% of them exhibited the four tested traits. Sequencing of a fragment of the 16S rRNA gene in selected high-performing isolates ascribed them to the Phyla Firmicutes (genera Bacillus and Paenibacillus ), Actinobacteria (genus Streptomyces ), and Proteobacteria (genus Inquilinus ). These findings open new possibilities for the improvement of Ni agromining with E. rufuschaneyi , which need to be confirmed by future inoculation experiments.