Combined Bioremediation of Bensulfuron-Methyl Contaminated Soils With Arbuscular Mycorrhizal Fungus and Hansschlegelia zhihuaiae S113

Abstract

Over the past decades, because of large-scale bensulfuron-methyl (BSM) application, environmental residues of BSM have massively increased, causing severe toxicity in rotation-sensitive crops. The removal of BSM from the environment has become essential. In this study, the combined bioremediation of the arbuscular mycorrhizal fungi (AMF) Rhizophagus intraradices and BSM-degrading strain Hansschlegelia zhihuaiae S113 of BSM-polluted soil was investigated. BSM degradation by S113 in the maize rhizosphere could better promote AMF infection in the roots of maize, achieving an infection rate of 86.70% on the 36th day in the AMF + S113 + BSM group. Similarly, AMF enhanced the colonization and survival of S113 in maize rhizosphere, contributing 4.65 × 10⁵ cells/g soil on the 15th day and 3.78 × 10⁴ cells/g soil on the 20th day to a population of colonized-S113 (based possibly on the strong root system established by promoting plant-growth AMF). Both S113 and AMF coexisted in rhizosphere soil. The BSM-degrading strain S113 could completely remove BSM at 3 mg/kg from the maize rhizosphere soil within 12 days. AMF also promoted the growth of maize seedlings. When planted in BSM-contaminated soil, maize roots had a fresh weight of 2.59 ± 0.26 g in group S113 + AMF, 2.54 ± 0.20 g in group S113 + AMF + BSM, 2.02 ± 0.16 g in group S113 + BSM, and 2.61 ± 0.25 g in the AMF group, all of which exceeded weights of the control group on the 36th day except for the S113 + BSM group. Additionally, high-throughput sequencing results indicated that simultaneous inoculation with AMF and strain S113 of BSM-polluted maize root-soil almost left the indigenous bacterial community diversity and richness in maize rhizosphere soil unaltered. This represents a major advantage of bioremediation approaches resulting from the existing vital interactions among local microorganisms and plants in the soil. These findings may provide theoretical guidance for utilizing novel joint-bioremediation technologies, and constitute an important contribution to environmental pollution bioremediation while simultaneously ensuring crop safety and yield.

Keywords: 16s sequencing; Hansschlegelia zhihuaiae S113; arbuscular mycorrhizal fungi; bensulfuron-methyl; combined bioremediation.

FIGURE 1

Infection of the Arbuscular mycorrhizal fungi (AMF) to the maize root system. (A) Rhizophagus intraradices colonization in maize roots, as observed under an optical microscope (200 ×). (a) (d) Root segment with low infection rate; (b) (e) Root segment with moderate infection rate; (c) (f) Root segment with high infection rate. The red arrows indicate spores; the yellow arrows indicate hyphae or mycelium. (B) The infection rate of AMF to maize root system under different treatments.

FIGURE 2

Confocal laser scanning microscope images of S113 colonization on maize roots. The treatment was irrigated with S113 or S113 + Arbuscular mycorrhizal fungi (AMF). The control was treated with sterile water.

FIGURE 3

Effects of Arbuscular mycorrhizal fungi (AMF) on the colonization of S113 in the rhizosphere and root surface. Dynamic of S113 population on roots surface and in the rhizosphere of maize under different treatments. The data are shown as log₁₀CFU per gram soil or roots. The error bars indicate standard deviations for three samples.

FIGURE 4

The residual concentration of Bensulfuron-methyl (BSM) in Rhizosphere soil.

FIGURE 5

The growth of maize under different treatments. (A) control (CK); (B) S113; (C) Bensulfuron-methyl (BSM); (D) Arbuscular mycorrhizal fungi (AMF); (E) S113 + BSM; (F) AMF + BSM; (G) S113 + AMF; (H) S113 + AMF + BSM. +: addition; −: without addition.

FIGURE 6

The growth of maize under different treatments. CK: the seedlings without Bensulfuron-methyl (BSM) and S113 or Arbuscular mycorrhizal fungi (AMF); S113: seedlings were inoculated with S113 by root irrigation; BSM: soils were treated with bensulfuron-methyl, 3.0 mg/kg; AMF: seedlings were inoculated with AMF spore suspension (200 μL); S113 + BSM: seedlings were treated with BSM and inoculated with S113; AMF + BSM: seedlings were treated with BSM and inoculated with AMF spore suspension; S113 + AMF: seedlings were inoculated with S113 and AMF spore suspension; S113 + BSM + AMF: seedlings were inoculated with S113 and AMF spore suspension, and soils were treated with BSM.

FIGURE 7

Shannon diversity index for microbial communities of different treatments on the 12th day and 36th day. Note: CK: the seedlings without Bensulfuron-methyl (BSM) and S113 or Arbuscular mycorrhizal fungi (AMF); S113: seedlings were inoculated with S113 by root irrigation; BSM: soils were treated with bensulfuron-methyl, 3.0 mg/kg; AMF: seedlings were inoculated with AMF spore suspension (200 μL); S113 + BSM: seedlings were treated with BSM and inoculated with S113; AMF + BSM: seedlings were treated with BSM and inoculated with AMF spore suspension; S113 + AMF: seedlings were inoculated with S113 and AMF spore suspension; S113 + BSM + AMF: seedlings were inoculated with S113 and AMF spore suspension, and soils were treated with BSM. Values with different letters are significantly different at the P < 0.05 according to Duncan’s test.

FIGURE 8

Relative abundance histograms for different treatments in genus level. The top 10 of total species abundance are displayed. Each color represents a different genus level species. CK: the seedlings without BSM and S113 or AMF; S113: seedlings were inoculated with S113 by root irrigation; BSM: soils were treated with bensulfuron-methyl, 3.0 mg/kg; AMF: seedlings were inoculated with AMF spore suspension (200 μL); S113 + BSM: seedlings were treated with BSM and inoculated with S113; AMF + BSM: seedlings were treated with BSM and inoculated with AMF spore suspension; S113 + AMF: seedlings were inoculated with S113 and AMF spore suspension; S113 + BSM + AMF: seedlings were inoculated with S113 and AMF spore suspension, and soils were treated with BSM.