Overview
This laboratory pot experiment isolated 13 trace-metal-tolerant plant-growth-promoting rhizobacteria (PGPR) from a cadmium- and zinc-contaminated soil tip in Balan, Transylvania, Romania, then tested two selected strains — Pseudomonas koreensis BB2.A.1 and Serratia liquefaciens BB2.1.1 — for their effects on 21-day-old Zea mays seedling growth, physiology, cadmium and zinc accumulation, and translocation under artificial trace-metal stress. The study documents cadmium uptake into maize shoots and roots under experimental solution concentrations (0.5 mM cadmium (Cd), far above agricultural soil levels) and the modest modulating effects of PGPR inoculation on that uptake. It does not measure cadmium or zinc in food-grade maize kernels, fresh sweet corn, or any retail matrix; all measured concentrations are in seedling shoot and root tissue under artificial stress conditions and are not transferable to food occurrence data.
Key numbers
Measured cadmium accumulation in maize plant tissue, expressed in micrograms per gram (dry weight) of shoot or root tissue, under 0.5 mM Cd2+ treatment (pot experiment; n = 5 plants per treatment):
Cadmium in shoot tissue (control uninoculated, 0.5 mM Cd): mean approximately 0.0019 micrograms per gram dry weight (read from Figure 7a; exact value not tabulated in text).
Cadmium in root tissue (control uninoculated, 0.5 mM Cd): mean approximately 0.012 micrograms per gram dry weight (read from Figure 7b).
Translocation factor (TF) for Cd, defined as shoot Cd divided by root Cd: 0.08 to 0.16 for Cd-treated samples with and without inoculation, indicating inhibited translocation from root to shoot (TF less than 1 means metal transfer is inhibited).
Zinc accumulation in shoot (control, 1 mM Zn): approximately 100 micrograms per gram dry weight; under 1 mM Zn with Serratia liquefaciens BB2.1.1 inoculation, approximately 231 micrograms per gram dry weight in shoot (statistically significant, p less than 0.05). These are seedling-tissue values under artificially elevated solution-phase zinc; they carry no implication for zinc in sweet corn kernels under field conditions.
Cadmium concentrations used in treatments (0.5 mM and 0.1 mM) are far above concentrations found in agricultural soils. The cadmium in lithosphere is cited by the authors as approximately 0.2 mg per kg; in sedimentary rocks approximately 0.3 mg per kg; in soil approximately 0.53 mg per kg. These background figures are drawn from published literature cited by the authors, not measured in this study.
No food-matrix concentration data are reported. LOD, LOQ, CRM recovery, and blank values are not reported for the plant tissue analysis; concentrations were determined by atomic absorption spectrophotometry after ashing at 450 degrees C.
Evidence Fitness
Context only. This paper documents the cadmium and zinc uptake pathway from soil to maize root and shoot tissue under controlled, artificially elevated metal stress conditions, with and without PGPR inoculation. It supports qualitative understanding of how cadmium enters the maize plant (root uptake, limited root-to-shoot translocation at high external cadmium) and how soil bacteria can modestly modulate that uptake. It does not provide occurrence data for cadmium, zinc, or any other metal in food-grade corn kernels, canned corn, frozen sweet corn, or any consumer product. Figures from this study must not be used as contamination profile values for corn ingredients.
Methods (brief)
Bacterial strains isolated from trace-metal-polluted soil (Balan, Transylvania, Romania) by serial dilution; 13 isolates screened, two selected (BB2.A.1 identified as Pseudomonas koreensis, BB2.1.1 as Serratia liquefaciens, by 16S rDNA sequencing deposited in EMBL). Maize variety Zea mays MV3122, surface-sterilized, germinated on wet filter paper; seedlings transplanted into sterilized soil (121 degrees C, 40 min); trace metal treatments applied to soil. Shoot and root dried to constant weight at 105 degrees C, ashed in Gefran 1001 incinerator at 450 degrees C for 4 hours, dissolved in 25% HNO3 and filled to 10 mL; cadmium and zinc determined by Varian Spectra AA 110 atomic absorption spectrophotometer. No CRM, LOD, LOQ, or recovery data reported. Statistical analysis by one-way ANOVA, Tukey test, Pearson correlation in Microsoft Excel 2019 and Past.exe 4.03.
Implications
Certification: This paper provides no food-concentration data for corn. It is not an input to HMT&C lot testing limits or contamination profile values for corn or maize.
Courses: Illustrates the cadmium uptake pathway in maize (soil cadmium enters root, is partly retained at root, translocation to shoot is limited) and introduces the concept of PGPR-assisted trace-metal management as an agricultural remediation approach.
App: No change to any ingredient contamination_profile block. This paper is context for the uptake-pathway section of corn ingredient pages only.
Microbiome: Relevant to WikiBiome. The PGPR strains (Pseudomonas koreensis, Serratia liquefaciens) are rhizosphere microorganisms that modulate cadmium and zinc mobility in the soil-plant interface. The finding that soil bacterial communities can alter metal translocation factors in maize is a microbiome-metals interaction worth flagging for the WikiBiome metals-and-microbiome bridge.
Related evidence
Update history
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