New Caledonia is an archipelago in the South Pacific known for its diverse and unique biodiversity, particularly on ultramafic substrates. These soils, characterized by high levels of heavy metals, deficiencies in essential plant nutrients and unbalanced Ca/Mg ratio, have facilitated the emergence of a unique biodiversity highly adapted to metal stress. Plant species known as metallophytes are found there, which are either capable of resisting, tolerating, accumulating, or even hyperaccumulating the metals naturally present in these soils. These metallophytes, and the ultramafic substrates they are growing on, represent particular ecological niches favouring the emergence of metal-resistant microorganisms. These microorganisms are of increasing interest in research due to their potential use in bioremediation or in the development of microbial-based biotechnologies. In the present study, we propose to explore the microbiomes associated with several Ni-hyperaccumulator (Ni-HA) and Ni-tolerant (Ni-T) endemic species from New Caledonia: Psychotria gabriellae (Ni-HA), Psychotria semperflorens (Ni-T), and Geissois pruinosa (Ni-HA). The objective is to select microbial strains with remarkable and exploitable properties for local ecological restoration strategies and the development of innovative microbial biotechnologies. To achieve this, bacteria and fungi resistant to nickel and showing plant growth-promoting (PGP) effects were isolated and characterized. Strains capable of growing on a medium enriched with Ni (500ppm) were tested and selected for the following PGP effects: nitrogen fixation (for bacteria), ammonia production (for fungi), siderophore and phytohormone (indole acetic acid) production, and phosphate solubilization. The selected strains were morphologically and molecularly characterized, and tests for exopolysaccharide production and biofilm formation in bacteria were conducted. Finally, building upon previous research, we established a correlation between selected microorganisms and metabarcoding data (16S and ITS genes) obtained from Psychotria species (P. gabriellae and P. semperflorens).