Role of plant growth promoting rhizobacteria and Ag-nano particle in the bioremediation of heavy metals and maize growth under municipal wastewater irrigation

Abstract

The investigation evaluated the role of plant growth promoting rhizobacteria (PGPR) and Ag-nano particle on the growth and metabolism of maize irrigated with municipal wastewater (MW). Three PGPR isolated from MW were identified on the basis of 16S-rRNA gene sequence analyses as Pseudomonas sp., Pseudomonas fluorescence, and Bacillus cereus. The municipal waste water was used to irrigate the maize seeds inoculated with 3 isolated PGPR. The isolated PGPR had catalase and oxidase enzymes, solubilize insoluble bound phosphate and exhibit antifungal and antibacterial activities. The colony forming unit (cfu) of the PGPR was inhibited by Ag-nano particle, but was stimulated by the municipal wastewater. The Ag-nano particles augmented the PGPR induced increase in root area and root length. The root-shoot ratio was also changed with the Ag-nano particles. The plants irrigated with municipal wastewater had higher activities of peroxidase and catalase which were further augmented by Ag-nano particle. The Ag- nano particle application modulated level of ABA (34%), IAA (55%), and GA (82%), increased proline production (70%) and encountered oxidative stress and augmented the bioremediation potential of PGPR for Pb, Cd, and Ni. Municipal wastewater needs to be treated with PGPR and Ag nano particle prior to be used for irrigation. This aims for the better growth of the plant and enhanced bioremediation of toxic heavy metals.