Lead: Natural Occurrence, Toxicity to Organisms and Bioremediation by Lead-degrading Bacteria: A Comprehensive Review Original paper

What was reviewed?

This comprehensive review synthesizes evidence on lead bioremediation by bacteria, spanning Pb’s natural occurrence, toxicodynamics across organisms, and the microbial toolkits that immobilize, export, or transform Pb(II) to reduce bioavailability. It explains how speciation in soils (soluble, exchangeable, organic-bound, and mineral-associated fractions) constrains plant and food-chain uptake, and why biological strategies—biosorption, bioaccumulation, biomineralization, and biotransformation—can outperform costly physical/chemical remediation for diffuse contamination. Mechanistically, the review details bacterial surface adsorption to peptidoglycan and exopolysaccharides, intracellular sequestration by metallothioneins, enzymatic precipitation (e.g., phosphatase-mediated Pb-phosphate and sulfate-reducer–driven PbS), and active efflux via P1B-type ATPases (including the pbr operon). It also highlights endophytic and rhizosphere consortia that mobilize or immobilize metals via siderophores, organic acids, and ACC deaminase, positioning plant–microbe systems as scalable, eco-compatible solutions.

Who was reviewed?

Evidence derives from contaminated soils, industrial effluents, riverine sediments, hot springs, and agricultural settings, integrating in vitro biosorption assays, pilot bioreactors, and plant–microbe phytoremediation trials. Bacterial taxa span Firmicutes (Bacillus spp., Lactobacillus spp.), Actinobacteria (Arthrobacter, Micrococcus), Proteobacteria (Pseudomonas, Stenotrophomonas, Variovorax, Alcaligenes), and thermophiles (Geobacillus), with additional observations in lactic acid bacteria derived from fermented foods and endophytes isolated from metallophyte roots. The review also contextualizes Pb toxicity across humans, livestock, fish, and plants, underlining why lowering environmental bioavailability is clinically meaningful, while reporting pH-, temperature-, and biomass-dependent performance characteristics that determine strain selection and deployment.

Most important findings

Across systems, bacteria consistently reduce aqueous Pb through rapid surface binding and precipitation, with capacity and kinetics shaped by pH (often optimal near 4–6 for adsorption), contact time, and microbial density. Lactic acid bacteria (e.g., Lactobacillus plantarum, L. acidophilus, L. brevis) and bifidobacteria exhibit metabolism-independent cell-wall binding and exopolysaccharide-mediated sequestration that can remove large fractions of dissolved Pb under bench conditions; similarly, Bacillus (including B. subtilis and B. gibsonii) achieves high adsorption capacities confirmed by FTIR/EDX, while Pseudomonas putida biomass displays fast, pH-sensitive biosorption. Field-relevant isolates such as Stenotrophomonas rhizophila and Variovorax boronicumulans can drive biomineralization within 72 hours, and thermophiles like Geobacillus thermodenitrificans retain activity in industrial wastewater matrices.

Functionally, the best-characterized genetic module is the pbr operon of Cupriavidus metallidurans, where PbrR activates the promoter upon Pb(II) sensing, PbrA (P1B-type ATPase) exports Pb(II), PbrB increases periplasmic phosphate to promote cell-surface precipitation, and accessory factors aid sequestration; beyond pbr, broad-specificity PIB-ATPases (e.g., ZntA-like systems) and metallothionein BmtA extend the “lead toolkit” across diverse bacteria. For a microbiome signatures database, the taxa most recurrently implicated include Lactobacillus/Bifidobacterium (high-affinity surface binding), Bacillus (robust adsorption and EPS), Pseudomonas/Stenotrophomonas (biosorption and biomineralization), and plant-associated endophytes that modulate bioavailability via siderophores and organic acids; functionally, EPS biosynthesis, phosphatase/urease, sulfate reduction, and P-type ATPase efflux represent salient, portable markers to index Pb-interacting communities.

Key implications

Clinically, diminishing environmental Pb bioavailability upstream reduces pediatric and obstetric risk from diet and dust, and the review supports pairing source control with bio-based remediation where excavation or chemical fixation is impractical. For practice-facing microbiome work, annotate samples with exposure tier, soil/water chemistry (pH, competing anions), and presence of Pb-responsive functions (EPS, phosphatases, sulfate reduction, PIB-ATPases, metallothioneins), because these traits predict real-world immobilization and influence measured Pb in stools or effluents. Probiotic LAB show promise for lowering gastrointestinal Pb bioaccessibility in vitro, but translation to therapy requires cautious validation; the most immediate application is environmental or food-chain mitigation using consortia tailored to local chemistry and host plants. Integrating these mechanism-based markers into microbiome databases will enable harmonized comparisons of Pb-associated taxa and functions across studies and settings.