Development and Evaluation of Zinc and Iron Nanoparticles Functionalized with Plant Growth-Promoting Rhizobacteria (PGPR) and Microalgae for Their Application as Bio-Nanofertilizers

Abstract

Micronutrient deficiencies are widespread and growing global concerns. Nanoscale nutrients present higher absorption rates and improved nutrient availability and nutrient use efficiency. Co-application of nanofertilizers (NFs) with biological agents or organic compounds increases NF biocompatibility, stability, and efficacy. This study aimed to develop and evaluate zinc and iron bio-nanofertilizers formulated with plant growth-promoting rhizobacteria (PGPR) and microalgae. Nanoparticles (NPs) were synthesized with the co-precipitation method and functionalized with Pseudomonas species and Spirulina platensis preparation. NPs were characterized and evaluated on seed germination, soil microbial growth, and early plant response under seedbed conditions. NPs corresponded to zinc oxide (ZnO; 77 nm) and maghemite (γ-Fe2O3; 68 nm). Functionalized nanoparticles showed larger sizes, around 145–233 nm. The seedling vigor index of tomato and maize was significantly increased (32.9–46.1%) by bacteria-functionalized ZnO- and γ-Fe2O3-NPs at 75 ppm. NFs at 250 and 75 ppm significantly increased bacterial growth. NFs also improved early plant growth by increasing plant height (14–44%), leaf diameter (22–47%), and fresh weight (46–119%) in broccoli and radish, which were mainly influenced by bacteria capped ZnO- and γ-Fe2O3-NPs at 250 ppm. Beneficial effects on plant growth can be attributed to the synergistic interaction of the biological components and the zinc and iron NPs in the bio-nanofertilizers.

Biofortification of Broccoli Microgreens (Brassica oleracea var. italica) with Glucosinolates, Zinc, and Iron through the Combined Application of Bio- and Nanofertilizers

“…Complete experimental strategy considering the formulation of biofertilizers based on plant growth-promoting rhizobacteria (a) as reported in Guardiola-Márquez et al [27]; the production and evaluation of zinc and iron bio-nanofertilizers (b) described by Guardiola-Márquez et al [39]; and the biofortification of broccoli microgreens with glucosinolates, zinc, and iron using the bio-and nanoformulations with the best performance in previous works (c). Zn Bac, bacteria functionalized ZnO NPs.…”

“…The synthesis and characterization process of the zinc and iron nanoparticles used in this study were previously reported in Guardiola-Márquez et al [39]. A co-precipitation method was used to synthesize hexagonal wurtzite ZnO nanoparticles (ZnO NPs; 76.84 ± 10.3 nm) from 0.5 M zinc acetate dihydrate (ZnC 4 H 6 O 4 •2H 2 O) solution as the start-ing material, and face-centered cubic maghemite (γ-Fe 2 O 3 -NPs; 67.7 ± 8.9 nm) using 0.3 M iron (II) sulfate heptahydrate (FeSO 4 •7H 2 O) and 0.6 M ferric chloride (FeCl 3 •6H 2 O) as the precursor solution for iron nanoparticles.…”

“…Bacterial species corresponded to four Pseudomonas species (Pseudomonas allii strain B5KEA, Pseudomonas marginalis strain B9M, Pseudomonas protegens strain A276, and Pseudomonas sesami strain A137A1) that were earlier isolated, characterized for several PGP traits and identified through DNA sequencing [27]. Further details of the NP functionalization and characterization process are presented in Guardiola-Márquez et al [39]. Bacteria capped ZnO and γ-Fe 2 O 3 NPs at 250 ppm were used in the present work as they presented the bio-nanofertilizing potential in the previous in vivo assays in broccoli and radish (Figure 1b) [39].…”

“…Further details of the NP functionalization and characterization process are presented in Guardiola-Márquez et al [39]. Bacteria capped ZnO and γ-Fe 2 O 3 NPs at 250 ppm were used in the present work as they presented the bio-nanofertilizing potential in the previous in vivo assays in broccoli and radish (Figure 1b) [39].…”

“…Three cavities (replicates) were evaluated per treatment. The assay was performed in plastic seedbeds of 72 cavities (5 × 5 × 6 cm), filled to 3 4 of their capacity with sterile black soil mixed with vermiculite (3:1 v/v) [27,39]. Commercial broccoli (Brassica oleracea L. var.…”