PGPR-Mediated Plant Growth Attributes and Metal Extraction Ability of Sesbania sesban L. in Industrially Contaminated Soils

Arafat Abdel Hamed Abdel Latef,Amir Abdullah Khan,Mohamed Hashem,Baber Ali,Omar M Ali,Muhammad Atif Azeem,Fuchen Shi,Hassan Javed Chaudhary,Nida Zainab,Suliman Mohammed Alghanem,Saad Alamri,Amna Amna,Mona H Soliman,Muhammad Farooq Hussain Munis,Tongtong Wang

doi:10.3390/agronomy11091820

Abstract

The release of harmful wastes via different industrial activities is the main cause of heavy metal toxicity. The present study was conducted to assess the effects of heavy metal stress on the plant growth traits, antioxidant enzyme activities, chlorophyll content and proline content of Sesbania sesban with/without the inoculation of heavy-metal-tolerant Bacillus gibsonii and B. xiamenensis. Both PGP strains showed prominent ACC-deaminase, indole acetic acid, exopolysaccharides production and tolerance at different heavy metal concentrations (50–1000 mg/L). Further, in a pot experiment, S. sesban seeds were grown in contaminated and noncontaminated soils. After harvesting, plants were used for the further analysis of growth parameters. The experiment comprised of six different treatments. The effects of heavy metal stress and bacterial inoculation on the plant root length; shoot length; fresh and dry weight; photosynthetic pigments; proline content; antioxidant activity; and absorption of metals were observed at the end of the experiment. The results revealed that industrially contaminated soils distinctly reduced the growth of plants. However, both PGPR strains enhanced the root length up to 105% and 80%. The shoot length was increased by 133% and 75%, and the fresh weight was increased by 121% and 129%. The proline content and antioxidant enzymes posed dual effects on the plants growing in industrially contaminated soil, allowing them to cope with the metal stress, which enhanced the plant growth. The proline content was increased up to 190% and 179% by the inoculation of bacterial strains. Antioxidant enzymes, such as SOD, increased to about 216% and 245%, while POD increased up to 48% and 49%, respectively. The results clearly show that the utilized PGPR strains might be strong candidates to assist S. sesban growth under heavy metal stress conditions. We highly suggest these PGPR strains for further implementation in field experiments.

Highlights

Heavy metal contamination is an environmental problem of great concern that negatively affects human health
The current study focused on the ability of plant growth-promoting rhizobacteria (PGPR), i.e., Bacillus xiamenesis and Bacillus gibsonii to produce ACC-deaminase, EPS- and IAA
We determined the effect of heavy metal-tolerant PGPR strains, i.e., B. gibsonii and B. xiamenensis, on the root shoot length, fresh and dry biomass, proline content and chlorophyll content, as well as the antioxidant activity

Summary

Introduction

Heavy metal contamination is an environmental problem of great concern that negatively affects human health. Various industrial and anthropogenic activities result in heavy metal soil contamination [1]. Because of the greater content of heavy metals, higher pH level, lower availability of essential nutrients, low organic matter and poor soil structure, metals are difficult to extract from contaminated soils. The removal of heavy metals and alleviation of their negative effects using green plants and their associated microbes is called phytoremediation/assisted phytoremediation [3]. Besides the removal of heavy metals, the phytoremediation process can be used to remediate hydrocarbons, pesticides and polychlorinated biphenyl. Plants usually handle the contaminants via various mechanisms and maintain the fertility of the soil without affecting the topsoil [4].

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Conclusion