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. 2023 Apr 13;11(4):371.
doi: 10.3390/toxics11040371.

The Difference between Rhizosphere and Endophytic Bacteria on the Safe Cultivation of Lettuce in Cr-Contaminated Farmland

Zheyu Wen  1 , Qizhen Liu  1 , Chao Yu  2 , Lukuan Huang  1 , Yaru Liu  1 , Shun'an Xu  1 , Zhesi Li  1 , Chanjuan Liu  1 , Ying Feng  1
Affiliations

The Difference between Rhizosphere and Endophytic Bacteria on the Safe Cultivation of Lettuce in Cr-Contaminated Farmland

Zheyu Wen et al. Toxics. .

Abstract

Chromium (Cr) is a major pollutant affecting the environment and human health and microbial remediation is considered to be the most promising technology for the restoration of the heavily metal-polluted soil. However, the difference between rhizosphere and endophytic bacteria on the potential of crop safety production in Cr-contaminated farmland is not clearly elucidated. Therefore, eight Cr-tolerant endophytic strains of three species: Serratia (SR-1~2), Lysinebacillus (LB-1~5) and Pseudomonas (PA-1) were isolated from rice and maize. Additionally, one Cr-tolerant strain of Alcaligenes faecalis (AF-1) was isolated from the rhizosphere of maize. A randomized group pot experiment with heavily Cr-contaminated (a total Cr concentration of 1020.18 mg kg-1) paddy clay soil was conducted and the effects of different bacteria on plant growth, absorption and accumulation of Cr in lettuce (Lactuca sativa var. Hort) were compared. The results show that: (i) the addition of SR-2, PA-1 and LB-5 could promote the accumulation of plant fresh weight by 10.3%, 13.5% and 14.2%, respectively; (ii) most of the bacteria could significantly increase the activities of rhizosphere soil catalase and sucrase, among which LB-1 promotes catalase activity by 224.60% and PA-1 increases sucrase activity by 247%; (iii) AF-1, SR-1, LB-1, SR-2, LB-2, LB-3, LB-4 and LB-5 strains could significantly decrease shoot the Cr concentration by 19.2-83.6%. The results reveal that Cr-tolerant bacteria have good potential to reduce shoot Cr concentration at the heavily contaminated soil and endophytic bacteria have the same or even better effects than rhizosphere bacteria; this suggests that bacteria in plants are more ecological friendly than bacteria in soil, thus aiming to safely produce crops in Cr-polluted farmland and alleviate Cr contamination from the food chain.

Keywords: Cr passivation; Cr-tolerant bacteria; Lactuca sativa L.; chromium; microbial remediation.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
S-CAT and S-SC activity in the rhizosphere soil of different treatments. (A): S-CAT activity in soil. (B) S-SC activity in soil. The same letter means no significant difference.
Figure 2
Figure 2
Total Cr and Cr (VI) concentration in the rhizosphere soil of different treatments. (A): Total Cr concentration in soil; (B): Cr (VI) concentration in soil. The same letter means no significant difference.
Figure 3
Figure 3
The growth of lettuce in different treatments.
Figure 4
Figure 4
The Cr uptake, translocation and bioaccumulation of plants in different treatments. The data are average of three replicates ± SE. (A): Cr concentration in shoot; (B): Cr accumulation in shoot; (C): Translocation factor; (D): Bioaccumulation factor. The same letter means no significant difference.
Figure 5
Figure 5
Correlation analysis of basic physicochemical properties, enzyme activities, Cr bioavailability in rhizosphere soil and Cr bioaccumulation in plant. Cr: soil total Cr content, Cr (VI): soil Cr (VI) content, F.W.: fresh weight, Ca: chlorophyll a, Cb: chlorophyll b, Ctotal: total chlorophyll, Cr-A: Cr accumulation in shoot, Cr-C: Cr concentration in shoot.
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