Occurrence of heavy metal-resistance in microflora from serpentine soil of Andaman

Our plain-English summary of Occurrence of heavy metal-resistance in microflora from serpentine soil of Andaman, by A. Pal, S. Dutta, P.K. Mukherjee, et al (Journal of Basic Microbiology, 2005).

The study

• Authors: A. Pal, S. Dutta, P.K. Mukherjee, A.K. Paul
• Journal: Journal of Basic Microbiology
• Published: 2005;45(3):207-18
• Cited by: 37 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Serpentine soils collected from Saddle Hills, Chidyatapu and Rutland of Andaman Islands, India were analyzed for physico-chemical and microbiological characteristics and compared with those from adjacent non-serpentine localities. The serpentine soils contained high levels of nickel (1740.0-8033.4 mg/kg dry soil), cobalt (93.2-533.4 mg/kg dry soil) and chromium (302.9-4437.0 mg/kg dry soil), in addition to 62-152 g of iron and 37-60 g of magnesium per kg dry soil. Characteristically the serpentine soils showed low microbial density (6.2-11.3 x 10(6) colony forming unit/g soil) and activity (1.7-3.5 microg fluorescein/g dry soil/h) than non-serpentine outcrops. Serpentine microbial population was dominated by bacteria which represented 5.12 to 9.5 x 10(6) cfu/g of soil, while the fungal population ranged from 0.17 to 3.21 x 10(6) cfu/g of soil. A total of 342 (200 from serpentine and 142 from non-serpentine soils) isolates were compared for Ni, Co and Cr resistance. Serpentine microflora was in general, highly resistant than non-serpentine ones and showed a metal-resistance profile of Cr > Ni > Co. Amongst the serpentine isolates, 8 and 11 bacteria tolerated > 12.0 mM Ni and > 16.0 mM Cr respectively, while 6 fungal isolates showed a minimum inhibitory concentration (MIC) value > 8.0 mM Co. These 25 serpentine strains also showed co-resistance to Cu, Zn and Mn but were sensitive to Hg and Cd. The selected bacterial isolates were resistant to ampicillin, penicillin G and polymyxin B, whereas fungal strains showed resistance to amphotericin B, nystatin and fusidic acid.

Copyright 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

In plain English

This field and laboratory study looked at microbes living in serpentine soils, which are naturally rich in metals, on the Andaman Islands, India. The article does not discuss asbestos or human health. The authors collected nine soil samples from core serpentine areas around nickel-hyperaccumulating plants and six from nearby non-serpentine areas at Saddle Hills, Chidyatapu and Rutland Island. Total nickel in the serpentine samples ranged from 1740.0 to 8033.4 mg/kg dry soil, against 34.6 to 159.3 mg/kg in nearby soils. Serpentine soils generally held fewer microbes (6.22 to 11.34 million colony-forming units per gram) than non-serpentine soils (7.9 to 19.5 million). Of 342 microbes isolated, the serpentine ones were generally more tolerant of nickel, cobalt and chromium in laboratory tests. For example, 62.3% of serpentine bacteria grew at 4 mM nickel, compared with 24.8% of non-serpentine bacteria. Serpentine isolates tolerated chromium most and cobalt least. Twenty-five highly resistant strains also tolerated copper, zinc and manganese but were sensitive to mercury and cadmium, and selected bacteria resisted several antibiotics. The authors concluded that the metal-rich soils favored selection of metal-resistant microorganisms.

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: Field soil survey with laboratory culture and metal-resistance testing of microbial isolates, comparing serpentine and non-serpentine soils
• Who was studied: Nine soil samples from core serpentine areas and six from adjoining non-serpentine areas at Saddle Hills, Chidyatapu and Rutland Island, Andaman Islands, India. From these, 342 microbial isolates were obtained: 200 serpentine and 142 non-serpentine. Collection dates are not stated.
• Exposure: Naturally metal-rich serpentine soil. In the laboratory, isolates were grown in increasing concentrations of nickel, cobalt and chromium, and selected strains were then tested against copper, cadmium, manganese, zinc and mercury. No asbestos fibers were studied.
• Main results:
  • Total nickel in core serpentine soil samples ranged from 1740.0 to 8033.4 mg/kg dry soil.
  • Soils from the surrounding non-serpentine localities had low nickel content, 34.6 to 159.3 mg/kg dry soil.
  • Microbial counts in serpentine soils (6.22 to 11.34 million cfu per gram) were in general lower than in adjacent non-serpentine soils (7.9 to 19.5 million cfu per gram). The ranges overlap, so the difference did not hold at every site.
  • Nickel: 62.3% of serpentine bacterial isolates grew at 4 mM nickel, compared with 24.8% of non-serpentine bacterial isolates.
  • Cobalt: 13 serpentine fungal isolates (34.2% of serpentine fungi) grew at 4 mM cobalt; no non-serpentine fungi tolerated this concentration.
  • Chromium: about 38.2% of core serpentine bacteria grew at 12 mM chromium, while only 14.5% of non-serpentine bacteria tolerated 8 mM chromium.
  • Serpentine microorganisms tolerated chromium most and cobalt least (chromium, then nickel, then cobalt).
  • The 25 selected highly metal-resistant serpentine strains were co-resistant to copper, zinc and manganese but sensitive to mercury and cadmium.
  • Among the other metals tested on these 25 strains, mercury was the most toxic, followed by cadmium.
  • Most of 19 selected metal-resistant serpentine bacteria were resistant to ampicillin, penicillin G, polymyxin B, bacitracin and kanamycin, but sensitive to chloramphenicol, streptomycin, erythromycin and tetracycline.
• The authors' conclusion: The authors concluded that the serpentine soils of Andaman, with their high nickel, cobalt and chromium content, favored selection of more metal-resistant microorganisms than non-serpentine soils.
• Limitations the authors state:
  • Isolating fungi by dilution plating on CZAPEK-DOX agar did not capture the full fungal population of the soils.
  • Testing in nutrient broth may have raised the measured minimum inhibitory concentrations, because organic components can bind metals.
  • The 19 bacteria tested for antibiotic sensitivity were too few to establish a link between Gram type and antibiotic sensitivity.

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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