Deciphering the enhanced translocation of Pb, Ni and Cd from artificially polluted soil to Chrysopogon zizanioides augmented with Bacillus xiamenensis VITMSJ3

Abstract

The translocation of heavy metals (HMs) from the rhizosphere to plant systems constitutes a fundamental mechanism governing HM uptake. Microbial augmentation has emerged as a promising strategy to enhance this process. The study investigates the mechanism of enhanced translocation of heavy metals (HMs) from artificially polluted soil to Chrysopogon zizanioides, facilitated by Bacillus xiamenensis VITMSJ3. Pb, Ni, and Cd translocation to the roots and shoots of C. zizanioides was examined, revealing a significant increase of over 15% in HM uptake upon treatment with Bacillus xiamenensis VITMSJ3 (Accession number MT822866). VITMSJ3 exhibited biofilm formation capabilities, attributed to quorum sensing molecule production, and demonstrated resistance to Pb and Ni upto 4000 ppm and Cd upto 450 ppm, respectively. Moreover, VITMSJ3 displayed plant growth-promoting bacterial (PGPB) traits such as, indole-3-acetic acid (IAA), phosphate, ammonia, siderophore, and hydrogen cyanide (HCN) production. Amplification of candidate genes responsible for HM resistance (pbr for Pb, ncc for Ni, cadA for Cd) corroborated the genetic basis of resistance. SEM-EDAX micrographs confirmed HM uptake and translocation along with the presence of VITMSJ3. Enzymatic analysis revealed the synthesis of superoxide dismutase (SOD), catalase (CAT), glutathione-S-transferase (GST), peroxidase (POD), and ascorbate peroxidase (APX), implicating their involvement in ROS detoxification. Overall, the study underscores the efficacy of B. xiamenensis VITMSJ3 in enhancing HM translocation, thereby elucidating its potential for phytoremediation applications.

Supplementary information: The online version contains supplementary material available at 10.1007/s13205-024-04001-x.

Keywords: Antioxidant enzymes; Biofilm; Plant growth promoting bacteria; Quorum sensing; Translocation.

Fig. 1

Electrophoresis of PCR amplified products for genes on Agarose gel (a) pbrA, (b) ncc, (c) CadA with a product amplified at 500 bp, 1058 bp and 1141 bp respectively

Fig. 2

Toxicity examination of VITMSJ3 against seeds of Glycine max, Vigna radiata, Vigna mungo and Cicer arietinum. (a–d) Seeds treated with tap water, uninoculated broth, supernatant and pellet; (e–g) Pb, Ni and Cd treated seeds in combination with VITMSJ3; (h–j) Pb, Ni and Cd treated seeds; (k and l) Relative Elongation Rate for radicle and plumule; (m–p) Germination rate for all the treated seeds (%). Bar indicate the mean ± standard error of mean (SEM), with a statistical significance at confidence level of p < 0.05, p < 0.01*

Fig. 3

Physiological changes in C. zizanioides after different treatments in experimental plants till the 45th day of exposure (a–d) Pb, Ni, and Cd-contaminated soil augmented with bacteria VITMSJ3 25 mg kg⁻¹, 50 mg kg⁻¹, 75 mg kg⁻¹, 100 mg kg⁻¹; (e, f) control plant; (g–j) Pb, Ni, and Cd-contaminated soil; 25 mg kg⁻¹, 50 mg kg⁻¹, 75 mg kg⁻¹, 100 mg kg⁻¹, (k) Change in shoot length; (l) root length, (m) Total chlorophyll content (n) Relative water content (%) in shoot samples of C. zizanioides. Bar indicate the mean ± (SEM), with a statistical significance at confidence level of p < 0.05, p < 0.01*. Images inset in (c) shows the leaf disc of vetiver from each treatments of pot culture on 45th day

Fig. 4

Pb and Ni and Cd uptake exposed for 15th, 30th and 45th day. (a, b, c) Pb content in root, shoot and soil; (d, e, f) Ni content in root, shoot and soil; (g, h, i) Cd content in root, shoot and soil by C. zizanioides exposed to control soil (C); Pb, Ni and Cd contaminated soil 25 mg kg⁻¹ (25P); 50 mg kg⁻¹ (50P); 75 mg kg⁻¹ (75P); 100 mg kg⁻¹ (100P) and Pb, Ni and Cd contaminated soil augmented with bacteria VITMSJ3 25 mg kg⁻¹ (25BP); 50 mg kg⁻¹ (50BP); 75 mg kg⁻¹ (75BP); 100 mg kg⁻¹ (100BP). Bar indicate the mean ± (SEM), with a statistical significance at confidence level of p < 0.05, p < 0.01*

Fig. 4

Pb and Ni and Cd uptake exposed for 15th, 30th and 45th day. (a, b, c) Pb content in root, shoot and soil; (d, e, f) Ni content in root, shoot and soil; (g, h, i) Cd content in root, shoot and soil by C. zizanioides exposed to control soil (C); Pb, Ni and Cd contaminated soil 25 mg kg⁻¹ (25P); 50 mg kg⁻¹ (50P); 75 mg kg⁻¹ (75P); 100 mg kg⁻¹ (100P) and Pb, Ni and Cd contaminated soil augmented with bacteria VITMSJ3 25 mg kg⁻¹ (25BP); 50 mg kg⁻¹ (50BP); 75 mg kg⁻¹ (75BP); 100 mg kg⁻¹ (100BP). Bar indicate the mean ± (SEM), with a statistical significance at confidence level of p < 0.05, p < 0.01*

Fig. 5

Translocation factor for (a) Pb, (b) Ni and (c) Cd by C. zizanioides exposed to control soil (C); Pb, Ni and Cd contaminated soil 25 mg kg⁻¹ (25P); 50 mg kg⁻¹ (50P); 75 mg kg⁻¹ (75P); 100 mg kg⁻¹ (100P) and Pb, Ni and Cd contaminated soil augmented with bacteria VITMSJ3 25 mg kg⁻¹ (25BP); 50 mg kg⁻¹ (50BP); 75 mg kg⁻¹ (75BP); 100 mg kg⁻¹ (100BP). Bar indicates the mean ± (SEM), with a statistical significance at a confidence level of p < 0.05, p < 0.01*

Fig. 6

Levels of (a) Protein (b) Proline (c) MDA (d) H₂O₂ content of C. zinanioides exposed for 15th, 30th and 45th days in control soil (C); Pb, Ni and Cd contaminated soil 25 mg kg_-¹ (25P); 50 mg kg⁻¹ (50P); 75 mg kg⁻¹ (75P); 100 mg kg⁻¹ (100P) and Pb, Ni and Cd contaminated soil augmented with bacteria VITMSJ3 25 mg kg⁻¹ (25BP); 50 mg kg⁻¹ (50BP); 75 mg kg⁻¹ (75BP); 100 mg kg.⁻¹ (100BP). Bar indicates the mean ± (SD), with a statistical significance at a confidence level of p < 0.05

Fig. 7

Levels of (a) SOD, (b) CAT, (c) APX, (d) POD content of C. zinanioides exposed for 15th, 30th and 45th days in control soil (C); Pb, Ni and Cd contaminated soil 25 mg kg⁻¹ (25P); 50 mg kg⁻¹ (50P); 75 mg kg⁻¹ (75P); 100 mg kg⁻¹ (100P) and Pb, Ni and Cd contaminated soil augmented with bacteria VITMSJ3 25 mg kg⁻¹ (25BP); 50 mg kg⁻¹ (50BP); 75 mg kg⁻¹ (75BP); 100 mg kg⁻¹ (100BP). Bar indicates the mean ± (SEM), with a statistical significance at a confidence level of p < 0.05, p < 0.01*

Fig. 8

Scanning electron microscopy images of the C. zizanioides plant tissues with EDAX showing Pb, Ni and Cd ions. (a, b) Control shoot with EDAX showing no Pb, Ni and Cd ions (c, d) Control root tissue with no deposited metals (e, f) Phytoremediation set-up shoot with severe disruption with minimal Pb, Ni and Cd ions (g, h) Phytoremediation set-up root tissue exposed to Pb, Ni and Cd 150 mg kg⁻¹ (100P) with slight ions uptake (i, j) Rhizoremediation treated shoot tissues exposed to Pb, Ni and Cd 100 mg kg.⁻¹ with bacteria VITMSJ3 (100P) with less disruption and higher uptake of Pb, Ni and Cd ions confirmed with EDAX (k, l) Rhizoremediation exposed with increased Pb, Ni and Cd ions (m) Colonization of bacterial biofilm of the root, (n) Presence of visible rod shaped bacteria with similar morphology of VITMSJ3

Fig. 8

Scanning electron microscopy images of the C. zizanioides plant tissues with EDAX showing Pb, Ni and Cd ions. (a, b) Control shoot with EDAX showing no Pb, Ni and Cd ions (c, d) Control root tissue with no deposited metals (e, f) Phytoremediation set-up shoot with severe disruption with minimal Pb, Ni and Cd ions (g, h) Phytoremediation set-up root tissue exposed to Pb, Ni and Cd 150 mg kg⁻¹ (100P) with slight ions uptake (i, j) Rhizoremediation treated shoot tissues exposed to Pb, Ni and Cd 100 mg kg.⁻¹ with bacteria VITMSJ3 (100P) with less disruption and higher uptake of Pb, Ni and Cd ions confirmed with EDAX (k, l) Rhizoremediation exposed with increased Pb, Ni and Cd ions (m) Colonization of bacterial biofilm of the root, (n) Presence of visible rod shaped bacteria with similar morphology of VITMSJ3

Fig. 9

Probable mechanism depicting the antioxidant defense mechanism highlighting the excessive oxidative stress generated due to targeted HMs toxicity. (a) Bacterial mechanism on heavy metal resistance; (b) Plant translocation and stress mechanism; (c) Anti-defense mechanism upon plant and bacterial conjugation