Chromium phytoextraction and physiological responses of the hyperaccumulator <i>Leersia hexandra</i> Swartz to plant growth-promoting rhizobacterium inoculation

doi:10.1007/s11783-023-1609-0

Front. Environ. Sci. Eng.

2023, Vol. 17

Issue (1) : 9 https://doi.org/10.1007/s11783-023-1609-0

RESEARCH ARTICLE

Chromium phytoextraction and physiological responses of the hyperaccumulator Leersia hexandra Swartz to plant growth-promoting rhizobacterium inoculation

Xuehong Zhang^1,², Yuanyuan Zhang¹, Dan Zhu³, Zhiyi Lin², Na Sun¹, Chang Su¹, Hua Lin²(

), Junjian Zheng¹(

)

¹. College of Life and Environmental Science, Guilin University of Electronic Technology, Guilin 541004, China
². College of Environmental Science and Engineering, Guilin University of Technology, Guilin 541004, China
³. College of Mathematics and Science, Wuhan Institute of Technology, Wuhan 430205, China

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Abstract

● Improved Cr phytoextration efficiency was achieved by B. cereus inoculation.

● B. cereus could produce plant-beneficial PGPR factors at diverse Cr stresses.

● Enhanced resistance of inoculated L. hexandra towards elevated Cr stress.

● The majority of Cr existed in the stable forms in the tissues of L. hexandra.

Phytoextraction is a promising option for purifying hexavalent chromium (Cr(VI))-laden wastewater, but the long remediation period incurred by poor growth rate of Cr hyperaccumulators remains a primary hindrance to its large-scale application. In this study, we performed a hydroponic experiment to evaluate the feasibility of promoting the growth and phytoextraction efficiency of Cr hyperaccumulator Leersia hexandra Swartz (L. hexandra) by inoculating plant growth-promoting rhizobacteria (PGPR) Bacillus cereus (B. cereus). In batch tests, the Cr(VI) removal rates of L. hexandra and B. cereus co-culture were greater than the sum of their respective monocultures. This was likely due to the microbial reduction of Cr(VI) to Cr(III), which is amiable to plant uptake. Besides, the PGPR factors of B. cereus, including indoleacetic acid (IAA) production, 1-aminocyclopropane-1-carboxylic acid deamination (ACCd) activity, phosphate solubilization capacity, and siderophore production, were quantified. These PGPR factors helped explain the biomass augmentation, root elongation and enhanced Cr enrichment of the inoculated L. hexandra in pot experiments. Despite the increased Cr uptake, no aggravated oxidative damage to the cell membrane was observed in the inoculated L. hexandra. This was attributed to its capacity to confront the increased intracellular Cr stress by upregulating both the activities of antioxidative enzymes and expression of metal-binding proteins/peptides. Moreover, L. hexandra could always conserve the majority of Cr in the residual and oxalic integrated forms with low mobility and phytotoxicity, irrespective of the B. cereus inoculation. These results highlight the constructed Cr hyperaccumulator-rhizobacteria consortia as an effective candidate for decontaminating Cr(VI)-laden wastewater.

Keywords Hexavalent chromium Hyperaccumulator Rhizobacteria Leersia hexandra Swartz Bacillus cereus Consortia

Corresponding Author(s): Hua Lin,Junjian Zheng

About author:

Tongcan Cui and Yizhe Hou contributed equally to this work.

Issue Date: 18 August 2022

Cite this article:

Xuehong Zhang,Yuanyuan Zhang,Dan Zhu, et al. Chromium phytoextraction and physiological responses of the hyperaccumulator Leersia hexandra Swartz to plant growth-promoting rhizobacterium inoculation[J]. Front. Environ. Sci. Eng., 2023, 17(1): 9.

URL:

https://academic.hep.com.cn/fese/EN/10.1007/s11783-023-1609-0
https://academic.hep.com.cn/fese/EN/Y2023/V17/I1/9

Fig.1 Cr(VI) removal performance of the L. hexandra monoculture, the B. cereus monoculture, and the B. cereus-L. hexandra co-culture system under Cr(VI) stress of 5 mg/L (a), 10 mg/L (b), and 20 mg/L (c), respectively. The optical density (OD₆₀₀) of the B. cereus monoculture and the B. cereus-L. hexandra co-culture system before and after cultivation (d), and the Cr(VI) reduction kinetics of B. cereus (e) under the initial Cr(VI) concentrations of 5–20 mg/L.

Fig.2 Effect of B. cereus on the biomass (a) and root length (b) of L. hexandra at the initial Cr(VI) concentrations of 5–20 mg/L. “+” refers to the series with B. cereus inoculation. “*” indicates a significant difference (P < 0.05), and “**” indicates an extremely significant difference ( P < 0.01) by comparing to the series without Cr stress.

Fig.3 Plant growth-promoting indexes of B. cereus: IAA production (a), ACC deaminase activity (b), phosphate solubilization (c), and siderophore production (d) under the initial Cr(VI) concentrations of 0–20 mg/L. “*” indicates a significant difference (P < 0.05), and “**” indicates an extremely significant difference ( P < 0.01) by comparing to the series without Cr stress.

Fig.4 Effects of B. cereus on the SOD activity (a), POD activity (b), and CAT activity (c) of L. hexandra under the initial Cr(VI) concentrations of 5–20 mg/L. “+” refers to the series with B. cereus inoculation. “*” indicates a significant difference (P < 0.05), and “**” indicates an extremely significant difference ( P < 0.01).

Fig.5 Effects of B. cereus on MTs (a), PCs (b), and the MDA content (c) of L. hexandra under the initial Cr(VI) concentrations of 5–20 mg/L. “+” refers to the series with B. cereus inoculation. “*” indicates a significant difference (P < 0.05), and “**” indicates an extremely significant difference ( P < 0.01).

Fig.6 Cr uptake in a single plant (a); and the Cr distribution in the roots and shoots of L. hexandra (b). “+” refers to the series with B. cereus inoculation. “*” indicates a significant difference (P < 0.05), and “**” indicates an extremely significant difference ( P < 0.01) by comparing with the series without the B. cereus inoculation.

Fig.7 Concentration of the residual Cr (a) and oxalic integrated Cr (b) as well as the relative distribution of the residual Cr (c) and the oxalic integrated Cr (d) in L. hexandra. “+” refers to the series with B. cereus inoculation. “*” indicates a significant difference (P < 0.05), and “**” indicates an extremely significant difference ( P < 0.01) by comparing to the series without B. cereus inoculation.

Fig.8 Schematic diagram of the mechanism revealing the B. cereus-assisted Cr enrichment by L. hexandra.

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