Earthquakes promote bacterial genetic exchange in serpentinite crevices

Our plain-English summary of Earthquakes promote bacterial genetic exchange in serpentinite crevices, by N. Yoshida, N. Fujiura (Astrobiology, 2009).

The study

• Authors: N. Yoshida, N. Fujiura
• Journal: Astrobiology
• Published: 2009;9(3):289-95
• Cited by: 2 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

We report the results of our efforts to study the effects of seismic shaking on simulated biofilms within serpentinite fissures. A colloidal solution consisting of recipient bacterial cells (Pseudomonas sp. or Bacillus subtilis), donor plasmid DNA encoded for antibiotic resistance, and chrysotile (an acicular clay mineral that forms in crevices of serpentinite layers) were placed onto an elastic body made from gellan gum, which acted as the biofilm matrix. Silica beads, as rock analogues (i.e., chemically inert mechanical serpentinite), were placed on the gellan surface, which was coated with the colloidal solution. A rolling vibration similar to vibrations generated by earthquakes was applied, and the silica beads moved randomly across the surface of the gellan. This resulted in the recipient cells' acquiring plasmid DNA and thus becoming genetically transformed to demonstrate marked antibiotic resistance. Neither Pseudomonas sp. nor B. subtilis were transformed by plasmid DNA when chrysotile was substituted for by kaolinite or bentonite in the colloidal solution. Tough gellan (1.0%) promoted the introduction of plasmid DNA into Pseudomonas sp., but soft gellan (0.3%) had no such effect. Genetic transformation of bacteria on the surface of gellan by exposure to exogenous plasmid DNA required seismic shaking and exposure to the acicular clay mineral chrysotile. These experimental results suggest that bacterial genetic exchange readily occurs when biofilms that form in crevices of serpentinite are exposed to seismic shaking. Seismic activity may be a key factor in bacterial evolution along with the formation of biofilms within crevices of serpentinite.

In plain English

This was a laboratory experiment with bacteria, not a study of people. The authors, at the University of Miyazaki, Japan, tested whether shaking similar to an earthquake could help bacteria take up loose DNA when chrysotile is present. They placed a solution containing bacteria (Pseudomonas sp. or Bacillus subtilis), plasmid DNA carrying an antibiotic-resistance gene, and ground chrysotile onto gellan gum, a gel used as an artificial biofilm. They then rolled silica beads over it. After shaking, both kinds of bacteria took up the plasmid and became antibiotic-resistant. No uptake occurred when kaolinite or bentonite replaced chrysotile, or when chrysotile was left out. The authors reported that crocidolite also allowed uptake. Using more beads and stronger shaking gave more uptake. For Pseudomonas sp., transformation efficiency was on the order of 10 to the third power colony-forming units per microgram of plasmid DNA on 1.0–1.5% gellan, and none was seen on 0.3% gellan. The authors wrote that these laboratory results suggest bacterial genetic exchange readily occurs when biofilms in serpentinite crevices are exposed to seismic shaking. The study did not examine natural biofilms or real earthquakes.

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 (model system of a biofilm on serpentinite rock, using bacteria, gellan gum and silica beads under simulated earthquake shaking)
• Who was studied: Bacteria: a Gram-negative Pseudomonas sp. strain (heavy metal–resistant, isolated from the underside of rock) and a Gram-positive Bacillus subtilis strain (ISW1214); work done at the University of Miyazaki, Japan; dates not stated
• Exposure: Ground chrysotile (purchased from Waco Chemical Co., Japan) suspended with bacteria and plasmid DNA, compared with kaolinite and bentonite; rolling vibration with silica beads for 60 s at 52–133 Gal (amplitude 1.5 cm) as simulated earthquake shaking
• Main results:
  • After rolling vibration in the presence of chrysotile and plasmid DNA, Pseudomonas sp. formed visible colonies on the antibiotic-containing gel, which the authors took as transformation to kanamycin resistance.
  • Bacillus subtilis subjected to rolling vibration acquired the plasmid pHY300PLK and tetracycline resistance.
  • For both bacteria, 50 silica beads gave more genetic exchange than 25 beads at 150 Gal, and the number of exchange events was directly proportional to vibration intensity.
  • When kaolinite or bentonite replaced chrysotile, neither bacterium acquired the plasmid DNA.
  • No genetic exchange was seen when the solution contained no chrysotile. The authors also reported genetic exchange with other needle-shaped minerals such as crocidolite, without giving data.
  • For Pseudomonas sp., transformation efficiency was on the order of 10 to the third power colony-forming units per microgram of plasmid DNA on 1.0–1.5% gellan gum. It was lower below 1.0%, and no transformed cells were seen on 0.3% gellan gum.
  • B. subtilis acquired the plasmid at an increased chrysotile concentration (printed as 1.0 mg/ml), but not at the lower concentration tested.
• The authors' conclusion: The authors concluded that their results suggest bacterial genetic exchange readily occurs when biofilms that form in serpentinite crevices are exposed to seismic shaking.

Topics

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

Medical terms in this study, explained in our Lexicon: Serpentinite, Chrysotile, Acicular.

Related studies

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• Comparison of 16S rRNA and 16S rDNA T-RFLP approaches to study bacterial communities in soil microcosms treated with chromate as perturbing agent — A. Mengoni, E. Tatti, et al. (2005)
• Serpentinite and the dawn of life — N.H. Sleep, D.K. Bird, et al. (2011)
• Discovery and application of the Yoshida effect: nano-sized acicular materials enable penetration of bacterial cells by sliding friction force — N. Yoshida (2007)
• Chrysotile asbestos fibers mediate transformation of Escherichia coli by exogenous plasmid DNA — N. Yoshida, T. Ikeda, et al. (2001)
• Escherichia coli cells penetrated by chrysotile fibers are transformed to antibiotic resistance by incorporation of exogenous plasmid DNA — N. Yoshida, K. Kodama, et al. (2002)

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