Enhanced Lead Phytoextraction by Endophytes from Indigenous Plants

TL;DR

This study isolated 12 endophytic strains from native plants at a Pb-contaminated Italian site and tested them, alone or with EDTA, in microcosms of *Brassica juncea* and *Helianthus annuus*. PGPR alone gave the greatest shoot Pb increase in *B. juncea*, while PGPR+EDTA was best in *H. annuus*, with NGS supporting plant-microbe interactions as key.

Key findings

• A consortium (SG_1) of 12 endophytic strains from *Lotus cornicolatus*, *Sonchus tenerrimus*, and *Bromus sterilis*, selected for at least three plant-growth-promoting traits, was used as inoculum.
• In *B. juncea*, PGPR alone was most effective for shoot Pb phytoextraction: shoots had approximately 24 times more Pb than control (4.82 vs. 0.20 mg kg⁻¹ in Table 3; abstract reports “up to 25 times”). PGPR+EDTA increased *B. juncea* root Pb accumulation by about 58 times compared with control, and shoot biomass increased 36.5% only in the combined treatment.
• In *H. annuus*, the combined PGPR+EDTA treatment gave the highest root and shoot Pb concentrations; the abstract reports up to three times more Pb uptake, with shoot values of 3.46 vs. 1.34 mg kg⁻¹ and root values of 42.0 vs. 2.14 mg kg⁻¹. Aerial biomass increased by 13.4% (PGPR alone) and 11.5% (PGPR+EDTA) compared with control.
• NGS showed communities dominated by Pseudomonadaceae (max 51%), Caulobacteraceae (max 30%), Xanthomonadaceae (max 18%), and Sphingomonadaceae (max 15%); Bacillaceae increased with inoculum from 2% in controls to 8% in PGPR *B. juncea* soil and 5–10% in PGPR *B. juncea* and EDTA+PGPR *H. annuus* soil, while Enterobacteraceae increased with EDTA in roots (0% to 4% for *B. juncea*; 14% to 27% for *H. annuus*).

Methods

• Soil was collected from six sampling points (SP1–SP6) at a 40,000 m² contaminated site in Italy and mixed into a composite Pb-soil. Microcosms contained 300 g Pb-soil sown with *B. juncea* var. Scala or *H. annuus* var. Paola and received control, PGPR (10⁸ CFU/g soil), or PGPR+EDTA 2 mM, with three replicates over about 30 days.
• Pb in soil, extracts, and plant tissues was quantified by ICP-OES; soil Pb bioavailability was assessed by sequential extraction with H₂O, KNO₃ 1 M, and EDTA 1%; biomass was recorded as dry weight; phytotoxicity was screened with *Lepidium sativum*; treatment effects used one-way ANOVA with Tukey’s test (p < 0.05).
• Endophytes were isolated from surface-sterilized roots of the three native species, characterized for PGP traits (IAA, siderophores, P solubilization, EPS, proteolytic activity, ammonia, biofilm, N fixation), and soil/root communities were analyzed by 16S Ion Torrent NGS.

Limitations

• The paper states that case studies showing positive PGPR-only assisted phytoextraction are limited and that new experiments with different plant species and endophytes are underway; no other limitations are explicitly stated.
• Evident from the text: the experiment is a short-term (about 30-day) pot microcosm study with three replicates and a single composite soil, so field-scale and longer-term performance are not demonstrated.
• Evident from the text: Pb contamination levels are inconsistently reported—earlier site values reached approximately 2200 mg kg⁻¹ and exceeded the 1000 mg kg⁻¹ industrial threshold, while the experimental Pb-soil total Pb was about 112 mg kg⁻¹; additionally, NGS sample 2R was excluded due to low data quality.