Inoculation of Brassica oxyrrhina with plant growth promoting bacteria for the improvement of heavy metal phytoremediation under drought conditions

Our plain-English summary of Inoculation of Brassica oxyrrhina with plant growth promoting bacteria for the improvement of heavy metal phytoremediation under drought conditions, by Y. Ma, M. Rajkumar, C. Zhang, et al (Journal of Hazardous Materials, 2016).

The study

• Authors: Y. Ma, M. Rajkumar, C. Zhang, H. Freitas
• Journal: Journal of Hazardous Materials
• Published: 2016;320:36-44
• Cited by: 111 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

The aim of this study was to investigate the effects of drought resistant serpentine rhizobacteria on plant growth and metal uptake by Brassica oxyrrhina under drought stress (DS) condition. Two drought resistant serpentine rhizobacterial strains namely Pseudomonas libanensis TR1 and Pseudomonas reactans Ph3R3 were selected based on their ability to stimulate seedling growth in roll towel assay. Further assessment on plant growth promoting (PGP) parameters revealed their ability to produce indole-3-acetic acid, siderophore and 1-aminocyclopropane-1-carboxylate deaminase. Moreover, both strains exhibited high resistance to various heavy metals, antibiotics, salinity and extreme temperature. Inoculation of TR1 and Ph3R3 significantly increased plant growth, leaf relative water and pigment content of B. oxyrrhina, whereas decreased concentrations of proline and malondialdehyde in leaves under metal stress in the absence and presence of DS. Regardless of soil water conditions, TR1 and Ph3R3 greatly improved organ metal concentrations, translocation and bioconcentration factors of Cu and Zn. The successful colonization and metabolic activities of P. libanensis TR1 and P. reactans Ph3R3 represented positive effects on plant development and metal phytoremediation under DS. These results indicate that these strains could be used as bio-inoculants for the improvement of phytoremediation of metal polluted soils under semiarid conditions.

Copyright © 2016 Elsevier B.V. All rights reserved.

In plain English

This article does not concern asbestos or human health. It was a laboratory and greenhouse experiment on plants and bacteria. The authors isolated 10 drought-resistant bacterial strains from the root zone of plants growing in serpentine soils in Portugal. They chose two, identified as Pseudomonas libanensis TR1 and Pseudomonas reactans Ph3R3, and grew the plant Brassica oxyrrhina in sterilized soil. Some pots had copper and zinc added (400 mg copper and 500 mg zinc per kg), some were kept under drought, and some had both. Compared with plants without bacteria, TR1 raised plant dry weight by 138% under drought, 403% under metal stress and 489% under both. TR1 raised copper content by 146% under metal stress and 161% under metal plus drought. Drought generally reduced copper and zinc uptake. Both strains survived in the soil under all stress conditions. The authors concluded that TR1 was the best strain for plant growth promotion and heavy metal phytoremediation under drought. They said the mechanisms still need study.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Laboratory screening of bacterial strains followed by a greenhouse pot experiment with plants (3 bacterial treatments crossed with 4 stress treatments)
• Who was studied: Bacterial strains taken from the root zone of Phleum phleoides and Trifolium repens grown in serpentine soils in northeast Portugal (10 drought-resistant strains isolated, 2 selected). The plants tested were Brassica oxyrrhina grown in pots of soil from the University of Coimbra Botanical Garden. No humans were studied.
• Exposure: Inoculation of plants with bacterial strains TR1 or Ph3R3; soil spiked with copper (400 mg per kg) and zinc (500 mg per kg); drought at 50% of field capacity. No asbestos or fibers were studied.
• Main results:
  • In the seedling screening under drought induced by polyethylene glycol, strain Ph3R3 increased shoot and root length by 67% and 59% compared with plants without bacteria.
  • Neither selected strain dissolved tricalcium phosphate. Both produced IAA, siderophores and ACC deaminase.
  • In plants inoculated with TR1, dry weight rose by 138% under drought, 403% under metal stress and 489% under drought plus metal stress, compared with plants without bacteria.
  • Under drought, TR1 increased leaf relative water content by 50% and Ph3R3 by 44%, compared with plants without bacteria.
  • TR1 reduced lipid peroxidation, a marker of oxidative damage, in leaves by 47% under drought, 48% under metal stress and 52% under both.
  • Drought generally reduced copper and zinc accumulation in plants.
  • In plants inoculated with TR1, copper content rose by 146% under metal stress and 161% under metal plus drought stress, compared with plants without bacteria.
  • Drought, metal stress and both together did not affect how well either strain colonized the soil around the roots.
• The authors' conclusion: The authors concluded that both strains improved plant growth, physicochemical status, leaf relative water content and phytoremediation potential of B. oxyrrhina under drought. They also concluded that TR1 was the best strain for plant growth promotion and heavy metal phytoremediation under drought.
• Limitations the authors state:
  • The authors stated that the mechanism by which the bacteria increase metal mobilization and uptake under drought was not analyzed and remains for further work.
  • The authors stated that TR1 still needs to be tested with other plant species and in metal-polluted field soils.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Chrysotile.

Medical terms in this study, explained in our Lexicon: Serpentine Group, Translocation.

Related studies

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• Characterization of metal-resistant plant-growth promoting Bacillus weihenstephanensis isolated from serpentine soil in Portugal — M. Rajkumar, Y. Ma, et al. (2008)
• Serpentine soils affect heavy metal tolerance but not genetic diversity in a common Mediterranean ant — F. Frizzi, A. Masoni, et al. (2017)
• Heavy metal sorption and desorption capacity of soils containing endogenous contaminants — E.F. Covelo, F.A. Vega, et al. (2007)
• Framework for assessment and phytoremediation of asbestos-contaminated sites — C. Gonneau, K. Miller, et al. (2017)
• Risk assessment and source analysis of heavy metals in soil around an asbestos mine in an arid plateau region, China — X. Li, D. Ding, et al. (2024)

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