Biodeterioration of asbestos cement by siderophore-producing Pseudomonas

Our plain-English summary of Biodeterioration of asbestos cement by siderophore-producing Pseudomonas, by S.R. David, A. Jaouen, D. Ihiawakrim, et al (Journal of Hazardous Materials, 2021).

The study

• Authors: S.R. David, A. Jaouen, D. Ihiawakrim, V.A. Geoffroy
• Journal: Journal of Hazardous Materials
• Published: 2021;403:123699
• Cited by: 10 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Since the ban on the use of asbestos due to its carcinogenic properties, the removal of asbestos cement, representing the major asbestos-containing waste, has proven to be a challenge in most industrial countries. Asbestos-containing products are mainly disposed of in landfills and have remained untreated. Bioremediation involving bacteria previously reported the ability of Pseudomonas aeruginosa to release iron from flocking asbestos waste through a siderophore-driven mechanism. We examined the involvement of siderophore-producing Pseudomonas in the biodeterioration of asbestos cement. Iron and magnesium solubilization were evaluated by specific siderophore-producing mutants. The absence of one of the two siderophores affected iron extraction, whereas equivalent dissolution as that of the control was observed in the absence of siderophore. Both pyoverdine and pyochelin biosynthesis was repressed in the presence of asbestos cement, suggesting iron bioavailability from the waste. We compared the efficiency of various pyoverdines to scavenge iron from asbestos cement waste that revealed the efficiency of all pyoverdines. Pyoverdines were efficient in iron removal extracted continuously, with no evident extraction limit, in long-term weathering experiments with these pyoverdines. The optimization of pyoverdine-asbestos weathering may allow the development of a bioremediation process to avoid the disposal of such waste in landfills.

Copyright © 2020 Elsevier B.V. All rights reserved.

In plain English

This laboratory study tested whether Pseudomonas bacteria, and iron-binding substances they make (siderophores called pyoverdine and pyochelin), can draw iron out of asbestos cement waste. The waste contained chrysotile fibers in a cement matrix and was ground before testing. Grown with the waste, the normal Pseudomonas aeruginosa strain dissolved 0.54 mg/L of iron. Strains lacking one siderophore dissolved 0.33 and 0.17 mg/L. A strain lacking both (0.08 mg/L) did not differ from the bacteria-free control (0.13 mg/L). Magnesium release did not differ significantly between any strain and the control. The asbestos cement strongly repressed the bacteria's siderophore production. All 10 pyoverdines tested dissolved iron, and those from P. aeruginosa and P. syringae tended to be the most efficient. Over 20 daily cycles these two removed 0.75 mg and 0.65 mg of iron in total, and iron was still being extracted at the end. Electron microscopy showed a large drop in iron in the chrysotile fibers. The authors concluded that the approach could contribute to eco-friendly management of asbestos waste. They said it should be tested on samples that have not been ground.

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 experiment on asbestos cement waste exposed to bacterial strains and bacterial siderophore (pyoverdine) solutions
• Who was studied: Asbestos cement waste (chrysotile in a cement matrix) obtained from CEFASC Environnement in France, tested with the wildtype Pseudomonas aeruginosa PAO1 strain, three siderophore-deficient mutants, and pyoverdines from 10 Pseudomonas strains
• Exposure: Ground asbestos cement containing chrysotile fibers, in 0.2 g samples, exposed to bacteria for 40 h or to pyoverdine-containing supernatants at 100 μM in cycles of 24 h to 96 h, including 20 renewal cycles of 24 h
• Main results:
  • Iron dissolved from asbestos cement was 0.54 mg/L with the wildtype strain, 0.33 mg/L without pyoverdine and 0.17 mg/L without pyochelin. The strain lacking both siderophores (0.08 mg/L) did not differ from the bacteria-free control (0.13 mg/L).
  • Magnesium release did not differ significantly between any bacterial strain and the control
  • Adding asbestos cement strongly repressed the bacteria's production pathways for both pyoverdine and pyochelin
  • All 10 pyoverdines tested dissolved iron. In the 96 h cycle, pyoverdines from P. syringae and P. aeruginosa removed 2.9 and 3.2 mg/L of iron versus 1.3 to 1.7 mg/L for the others. Some of these differences were not statistically significant.
  • Over 20 renewal cycles of 24 h, cumulative iron removed was 0.75 mg with the P. aeruginosa pyoverdine and 0.65 mg with the P. syringae pyoverdine. The authors report this as 34 % and 27 % of the iron in the sample.
  • Electron microscopy of chrysotile fibers after long-term treatment showed a large decrease in iron content with each pyoverdine. Magnesium content did not decrease after treatment with the P. syringae pyoverdine.
• The authors' conclusion: The authors concluded that breakdown of asbestos cement waste by siderophore-producing Pseudomonas could contribute to eco-friendly asbestos waste management, which they said would reduce asbestos-related environmental and health problems and landfill disposal.
• Limitations the authors state:
  • The waste was ground, which may explain the higher efficiency. The authors say the treatment should be tested on samples that have not been ground.
  • The long-term experiment was stopped after 20 cycles because it was time consuming, so the extraction limit was not reached
  • Further studies are needed to understand iron dissolution and confirm the authors' hypotheses

Topics

Medical terms in this study, explained in our Lexicon: Asbestos-Cement, Carcinogenic.

Related studies

• Iron removal from raw asbestos by siderophores-producing Pseudomonas — S.R. David, D. Ihiawakrim, et al. (2020)
• Engineering siderophore production in Pseudomonas to improve asbestos weathering — M. Lemare, H. Puja, et al. (2022)
• A Review of Asbestos Bioweathering by Siderophore-Producing Pseudomonas: A Potential Strategy of Bioremediation — S.R. David, V.A. Geoffroy (2020)
• Flocking asbestos waste, an iron and magnesium source for Pseudomonas — S.R. David, S. Fritsch, et al. (2020)
• Siderophore-mediated iron removal from chrysotile: Implications for asbestos toxicity reduction and bioremediation — S.K. Mohanty, C. Gonneau, et al. (2018)
• Serpentine endophytic bacterium Pseudomonas azotoformans ASS1 accelerates phytoremediation of soil metals under drought stress — Y. Ma, M. Rajkumar, et al. (2017)

Browse more research in Journal of Hazardous Materials, or return to medical research.