Isolation, characterization, and evaluation of a high-siderophore-yielding bacterium from heavy metal-contaminated soil.

Yajun Wang,Fangbo Yu,Wei Huang,Yaqian Li,Petri Penttinen

doi:10.1007/s11356-021-15996-8

Abstract

Heavy metal-resistant siderophore-producing bacteria (SPB) with plant growth-promoting traits can assist in phytoremediation of heavy metal-contaminated soil. We isolated siderophore-producing bacteria from Pb and Zn mine soil in Shangyu, Zhejiang, China. The isolate with the highest siderophore production, strain SX9, was identified as Burkholderia sp. Burkholderia sp. SX9 produced catecholate-type siderophore, with the highest production at a pH range of 6.0 to 8.0, a temperature range of 20 to 30 °C and NaCl concentration below 2%. Siderophore production was highest without Fe3+ and became gradually lower with increasing Fe3+ concentration. Minimal inhibitory concentrations (MIC) of Pb2+, Zn2+, Cu2+, and Cd2+ were 4000, 22000, 5000, and 2000 μmol L-1, respectively. The strain had a strong metal solubilization ability: the contents of Cu2+, Zn2+, and Cd2+ in the supernatant were 47.4%, 133.0%, and 35.4% higher, respectively, in strain SX9-inoculated cultures than in the not inoculated controls. The siderophore produced by strain SX9 could combine with Fe3+, Zn2+, and Cd2+ with good effectiveness. The plant growth-promoting traits of the strain included indole acetic acid (IAA) production, 1-aminocyclopropane-1-carboxylate (ACC) deaminase activity, and phosphate solubilization capability. Compared to the uninoculated growth medium and SX9 culture supernatant, the germination rate of Lolium perenne seeds was higher when inoculated with strain SX9 culture. In the experiment of seed germination, adding bacterial culture or supernatant could alleviate the toxicity of heavy metals to L. perenne seed germination. Under Cu2+ and Zn2+ stress, strain SX9 promoted the germination rate. Taken together, Burkholderia sp. SX9 had properties beneficial in the microbial enhancement of phytoremediation of soil contaminated with heavy metals.

Highlights

The contamination of soil with heavy metals poses major environmental and human health challenges, calling for the remediation of the contaminated soils
We investigated the complexation capacity of siderophore produced by strain SX9 for metal ions and the plant growth promoting characteristics of strain SX9, including its ability to promote the growth of Lolium perenne under heavy metal stress
Transmission electron microscopy (TEM) showed that SX9 cells were rod-shaped with multiple polar flagella (Fig. 2)

Summary

Introduction

The contamination of soil with heavy metals poses major environmental and human health challenges, calling for the remediation of the contaminated soils. Heavy metals are removed from the soil using physical, chemical and biological technologies. Each remediation technique has its own advantages and disadvantages in terms of pollutant removal and cost efficiency (Khalid et al 2016). Phytoremediation technology has attracted attention due to its economic, environmental friendly and non-secondary pollution characteristics (Ashraf et al 2019). The discovery of hyperaccumulator plants has enhanced the prospects for phytoremediation. Most of the hyperaccumulators grow and produce biomass slowly, requiring long remediation periods that diminish their applicability in phytoextraction (Ashraf et al 2019; Kuppusamy et al 2016)

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