Stress-dependent stability of microbial sulfidogenic bioremediation is governed by community assembly and...

In sulfidogenic treatment systems, toxic metal contamination challenges the stability of sulfate-reducing bacterial (SRB) communities that immobilize dissolved metals, yet the mechanisms by which metal-stress intensity drives divergent remediation performance across contamination gradients remain poorly understood. Here, we experimentally exposed a sulfidogenic microbial community to a controlled nickel (Ni) stress gradient and integrated ecological process modelling with genome-resolved population genomics to determine how stress intensity regulates remediation performance. Moderate Ni stress promoted stochastic-dominated community assembly, preserved taxonomic and population genetic diversity (high nucleotide diversity and low population-level ANI), and sustained metal removal performance. In contrast, high Ni stress imposed strong deterministic filtering, reduced α-diversity, homogenized community composition, induced pronounced genetic bottlenecks, and coincided with functional decline. Population-genomic analyses of dominant metal-removing lineages revealed contrasting evolutionary modes: a slow-growing lineage (Desulfococcus) employs a constitutive, diversity-preserving strategy, while a relatively fast-growing lineage (Desulfobulbus) adopts an inducible, sweep-prone response under high stress. Together, these findings establish a mechanistic pathway linking metal stress intensity, microbial assembly regimes, evolutionary dynamics, and remediation stability, improving the predictability of microbial metal immobilization processes in contaminated environments.