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Background <p>Industrial wastewater contaminates agricultural soils with potentially toxic elements, deteriorating soil health, crop productivity and food security. In contrast, plant growth-promoting (PGP) rhizobacteria tolerate metal toxicity and enhances plant growth.</p> Methods <p>This study explored metal-resistant bacteria in rhizosphere soils of onion plants irrigated with industrial wastewater in Khyber Pakhtunkhwa Province (Pakistan), analyzing in vitro PGP traits of bacteria under control and metal-stress conditions.</p> Results <p>Four strains, including <i>Bacillus velezensis</i>, <i>Bacillus cereus</i>, <i>Bacillus amyloliquefaciens</i>, and <i>Bacillus vallismortis</i> showed high resistance to target metals, including Cd, Cr, Pb, Ni, and Zn. The soil was marginally acidic (pH 6.2), with metal concentration pattern of Zn &gt; Ni &gt; Pb &gt; Cr &gt; Cd. Among the isolates, <i>B. cereus</i> displayed the highest minimum inhibitory for Zn (121&#xa0;mM), and <i>B. vallismortis</i> for Cd (64&#xa0;mM). Both strains also exhibited high tolerance to Pb (68&#xa0;mM), Cr (69&#xa0;mM), and Ni (72 and 70&#xa0;mM, respectively). <i>B. amyloliquefaciens</i> showed the highest reduction efficiency for Cr (60&#xa0;h). <i>B. cereus</i> exhibited the best overall PGP profile, with robust positive activity for all traits. Quantitatively, 1<b>-</b>aminocyclopropane-1-carboxylate<b> (</b>ACC) deaminase activity was highest in <i>B. cereus</i>, particularly under Ni, Zn, and Pb (99, 98, and 97&#xa0;µmol α-ketobutyrate mg⁻<sup>1</sup> protein h⁻<sup>1</sup>, respectively) exposure. <i>B. velezensis</i> showed enhanced siderophore production when exposed to Cd (37%) and Zn (42%), while <i>B. amyloliquefaciens</i> and <i>B. cereus</i> showed high production levels (38%–39%) under Zn stress. Furthermore, <i>B. amyloliquefaciens</i> showed robust capacity for phosphate solubilization, nitrogen fixation, and the production of indole acetic acid and ammonia across multiple metal treatments, particularly Zn.</p> Conclusion <p>These findings suggest that <i>Bacillus</i> strains possess PGP properties under metal stress conditions, indicating their potential for application in the remediation of metal-contaminated soils and enhancement of plant growth.</p>

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Unveiling the plant growth-promoting and bioremediation potential of bacteria isolated from onion rhizosphere soils irrigated with industrial wastewater

  • 期刊论文

  • 发表日期：

    2026年7月9日

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  • Aisha Bibi,
  • Sadia Alam,
  • Alia Naz,
  • Wisal Shah,
  • Ajmal Khan,
  • Mashael Daghash Alqahtani,
  • Abdelrahman R. Ahmed

摘要

Background

Industrial wastewater contaminates agricultural soils with potentially toxic elements, deteriorating soil health, crop productivity and food security. In contrast, plant growth-promoting (PGP) rhizobacteria tolerate metal toxicity and enhances plant growth.

Methods

This study explored metal-resistant bacteria in rhizosphere soils of onion plants irrigated with industrial wastewater in Khyber Pakhtunkhwa Province (Pakistan), analyzing in vitro PGP traits of bacteria under control and metal-stress conditions.

Results

Four strains, including Bacillus velezensis, Bacillus cereus, Bacillus amyloliquefaciens, and Bacillus vallismortis showed high resistance to target metals, including Cd, Cr, Pb, Ni, and Zn. The soil was marginally acidic (pH 6.2), with metal concentration pattern of Zn > Ni > Pb > Cr > Cd. Among the isolates, B. cereus displayed the highest minimum inhibitory for Zn (121 mM), and B. vallismortis for Cd (64 mM). Both strains also exhibited high tolerance to Pb (68 mM), Cr (69 mM), and Ni (72 and 70 mM, respectively). B. amyloliquefaciens showed the highest reduction efficiency for Cr (60 h). B. cereus exhibited the best overall PGP profile, with robust positive activity for all traits. Quantitatively, 1-aminocyclopropane-1-carboxylate (ACC) deaminase activity was highest in B. cereus, particularly under Ni, Zn, and Pb (99, 98, and 97 µmol α-ketobutyrate mg⁻1 protein h⁻1, respectively) exposure. B. velezensis showed enhanced siderophore production when exposed to Cd (37%) and Zn (42%), while B. amyloliquefaciens and B. cereus showed high production levels (38%–39%) under Zn stress. Furthermore, B. amyloliquefaciens showed robust capacity for phosphate solubilization, nitrogen fixation, and the production of indole acetic acid and ammonia across multiple metal treatments, particularly Zn.

Conclusion

These findings suggest that Bacillus strains possess PGP properties under metal stress conditions, indicating their potential for application in the remediation of metal-contaminated soils and enhancement of plant growth.