Characterization of metal-resistant plant-growth promoting Bacillus weihenstephanensis isolated from serpentine soil in Portugal

Our plain-English summary of Characterization of metal-resistant plant-growth promoting Bacillus weihenstephanensis isolated from serpentine soil in Portugal, by M. Rajkumar, Y. Ma, H. Freitas (Journal of Basic Microbiology, 2008).

The study

• Authors: M. Rajkumar, Y. Ma, H. Freitas
• Journal: Journal of Basic Microbiology
• Published: 2008;48(6):500-8
• Cited by: 37 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

A metal-resistant bacterial strain SM3 isolated from a serpentine soil in the north-east of Portugal was characterized as Bacillus weihenstephanensis based on the morphological and biochemical characteristics and on the comparative analysis of the partial 16S ribosomal DNA sequence. Bacillus weihenstephanensis SM3 showed a high degree of resistance to nickel (1500 mg l(-1)), copper (500 mg l(-1)) and zinc (700 mg l(-1)) and also to antibiotics (ampicillin, penicillin, kanamycin and streptomycin). Strain SM3 has also exhibited the capability of solubilizing phosphate and producing indole-3-acetic acid (IAA) both in the absence and in the presence of metals (Ni, Cu and Zn). A pot experiment was conducted to elucidate the effects of strain SM3 on plant growth and uptake of Ni, Cu or Zn by Helianthus annuus. Inoculation with strain SM3 increased the shoot and root biomass of H. annuus grown in both non-contaminated and contaminated soil. Furthermore, strain SM3 increased the accumulation of Cu and Zn in the root and shoot systems. A batch experiment was also conducted to assess the metal mobilization potential of strain SM3 in soil. Inoculation with this strain increased the concentrations of water soluble Ni, Cu and Zn in soil. Metal solubilization by this bacterial strain may be an important process to promote the uptake of heavy metals by plants. This study elucidates the multifarious role of strain SM3 in plant growth promotion and its metal mobilizing potential.

In plain English

This laboratory and greenhouse study examined bacteria from a serpentine soil in Bragança, north-east Portugal. It is about the metals nickel, copper and zinc; the article does not mention asbestos. Of 35 metal-resistant bacterial strains isolated, the authors selected strain SM3, identified as Bacillus weihenstephanensis, because it tolerated nickel up to 1500 mg per litre, copper up to 500 mg per litre and zinc up to 700 mg per litre. It also resisted four antibiotics. In culture it dissolved phosphate and produced the plant hormone IAA, although nickel and copper cut its phosphate dissolving by 43% and 17%. Sunflower seedlings treated with SM3 and grown in soil spiked with metals weighed more than untreated plants. In nickel-spiked soil their fresh weight was 47% higher. Treated plants had higher copper and zinc levels but lower nickel levels. SM3 raised water-soluble nickel, copper and zinc in soil by 13%, 24% and 75%. The authors concluded that such bacteria might have some potential to improve phytoextraction, meaning the removal of metals from soil by plants.

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 study of a soil bacterium, including a greenhouse pot experiment with sunflowers and a soil batch experiment
• Who was studied: Bacterial strains isolated from a serpentine soil site in Bragança, north-east Portugal (35 metal-resistant strains, one of them selected). Sunflower (Helianthus annuus) seedlings were grown in pots of garden soil from the University of Coimbra, eight plants per pot. No sampling dates are given.
• Exposure: Heavy metals nickel, copper and zinc, not asbestos. Soil was spiked to 200 mg per kg soil of each metal, and culture media contained 100 to 2000 mg per litre for tolerance tests.
• Main results:
  • Of 35 metal-resistant strains, strain SM3 was chosen for its tolerance to nickel up to 1500 mg per litre, copper 500 mg per litre and zinc 700 mg per litre.
  • Strain SM3 was identified as Bacillus weihenstephanensis, with 99% sequence similarity.
  • Strain SM3 resisted ampicillin, penicillin, kanamycin and streptomycin.
  • In culture, copper and nickel reduced phosphate solubilization by strain SM3 by 17% and 43% respectively, compared with the metal-free control.
  • IAA production by strain SM3 was reported as not adversely affected by the metals.
  • In nickel-contaminated soil, inoculated sunflowers had 47% higher fresh weight and 23% higher dry weight than non-inoculated plants. The authors' table marks the dry-weight difference in nickel soil as not statistically significant.
  • In copper-contaminated soil, inoculated sunflowers had 35% higher fresh weight and 16% higher dry weight than non-inoculated plants.
  • Inoculation increased copper and zinc accumulation in sunflower roots and shoots, but decreased nickel accumulation by 14% in roots and 48% in shoots.
  • In the table, shoot metal levels in non-inoculated versus inoculated plants were: copper 23.3 vs 38.0 mg per kg dry weight, zinc 224.0 vs 303.3, and nickel 34.3 vs 18.0. These shoot differences are lettered as significant. The root values all carry the same letter, which by the table's note means they were not significantly different.
  • After 10 days, soil inoculated with strain SM3 had 13% more water-soluble nickel, 24% more copper and 75% more zinc than control soil.
  • SM3 cells took up the most nickel (8.13 mg per g dry weight within 6 hours) and the least zinc (3.88 mg per g dry weight).
• The authors' conclusion: The authors concluded that inoculating plants with metal-resistant serpentine bacteria might have some potential to improve phytoextraction efficiency in metal-contaminated soils.
• Limitations the authors state:
  • The authors said comparison with other studies of bacterial metal tolerance was difficult because those studies used different growth media and incubation conditions.
  • The authors did not identify the compounds by which strain SM3 mobilizes metals, and said further work is needed.

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.

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