Root endophytic bacteria from Indocalamus decorus exhibit contrasting patterns in assisted phytoremediation under Pb–Zn contamination

Heavy metal contamination in lead-zinc tailing areas poses severe environmental risks. Microbe-assisted phytoremediation is a promising eco-friendly strategy, yet the root endophytic bacterial resources of the tolerant bamboo Indocalamus decorus remain largely unexplored. We recovered culturable root endophytic bacteria from I. decorus established for nearly three years in a tailing area, screened isolates for Pb tolerance and plant growth-promoting (PGP)-associated traits, and compared selected isolates in a controlled pot experiment. Of 73 isolates, 28 tolerated Pb across 300–1000 mg L⁻¹, and 18 showed diverse PGP-associated profiles. Sequential RSR screening and quantitative assays selected four isolates tentatively affiliated with Streptomyces shaanxiensis (RA12), Chryseobacterium gleum (RB32), Pseudomonas canavaninivorans (RB14), and Klebsiella sp. (RB31). Inoculation increased biomass and altered stress-related and rhizosphere nutrient indicators relative to the non-inoculated control, with RB14 and RA12 showing stronger growth-related responses. Pb partitioning differed among isolates: RB14 produced the highest root Pb concentration (1.75-fold of the control) and a low translocation factor (TF = 0.22), whereas RB32 produced the highest TF (0.79) and comparatively higher shoot Pb concentrations. Zn responses were less uniform; RB14 reduced root Zn concentration, whereas the other isolates generally increased Zn uptake. PCA-derived scores distinguished growth and stress, metal-partitioning, and combined multivariate responses, but the rankings were specific to the selected indicator sets. These results identify culturable endophytic isolates with contrasting effects on plant performance and Pb–Zn partitioning under controlled conditions. Validation in actual tailing substrates is required before environmental application.