02 October, 2011

In the ancient ice found bacteria resistant to antibiotics

 Permafrost on Alaska: in some places ice has age of 30 thousand years. For scientific most different specialities these ices give unique possibility to glance in the past. A photo from a site alaska-in-pictures.com  

 The Canadian scientists investigated DNA fragments, prisoners in a piece of ancient ice. By these fragments it was possible not only to define, what plants and animals lived in the given district 30 thousand years ago, but also to find out some properties of microbic community of those epoch. It has appeared that ancient bacteria already then had genes of stability to antibiotics. This conclusion all-important for understanding of mechanisms of formation of stability to modern medicinal antibiotics. Scientists have underlined that resistance genes to modern preparations frequently do not appear de novo, and simply get out of already available set.

Since opening of antibiotics has passed seven-eight decades, the problem of infections steady against antibiotics has the same age also. As invent new superstrong antibiotics, on the average in a year-two the preparation loses the super-power properties, and through ten years already becomes ineffective. Resistant strains bacteria arise extremely operatively , and natural selection promotes their fast distribution.
It was supposed that as a starting point of formation of resistance the successful mutation serves. And further to multiply and extend successful mutants absolutely easy. Scientists, however, frequently surprised also speed from which the necessary mutation is found out in population, and speed from which it extends, appearing simultaneously in different parts of the world. This phenomenon was written off for considerable speed mutation at bacteria and on parallel occurrence of the necessary signs. The Canadian scientists from University Makmastera (Hamilton, state of Ontario) have offered other explanation to the given phenomenon. For this purpose they used a unique material and have simultaneously shown brilliant possibilities of modern biology.

What for a material to them has got? It were two pieces of ice from a permafrost on the Bear stream on Klondike, blocked from above volcanic adjournment. The age of ice measured by several independent methods, was estimated in 30 thousand years. Differently, 30 thousand years ago on lake deposits the thick ever-frozen layer with characteristic seasonal structures was generated, then there was a volcano eruption, ice was blocked ash deposits; they, in turn , from above were gradually closed by loessial deposits and soil. Pressed frozen adjournment in this place have characteristic orderliness which testifies that after eruption of a volcano ice did not thaw . Everything that for today frozen in this ice, has got there 30 thousand years ago, instead of later with thawed snow.

The schematical image of sequence of deposits, two pieces of ice (two black circles) and silhouettes of the animals defined on 12s-rRNK whence have been chosen. Drawing from discussed article in Nature  

Ice in this case has appeared is similar to an amber piece in which inhabitants of ancient times have forever got stuck. But now scientists have applied much more modern methods of research instead of simple scrutiny the tarred amber front sights and needles. They have defined fragments of the frozen nucleinic acids. Particularly, scientists focused attention on mitochondrial ribosomal РНК (рРНК) and DNA. And by these fragments have defined, what animals and plants existed at the moment of frozen ground formation. Surprisingly — only one piece of ice is capable to give a portrait of the disappeared flora and fauna!

On the right — a quantitative parity of fragments рРНК from superficial ice (modern inhabitants) and at the left — from a permafrost (an ancient material). Apparently, modern "fauna" sharply differs from плейстоценовой. The scheme from additional materials to discussed article in Nature  

Then, in late Pleistocene, on Klondike it was possible to meet bisons, horses, rams, partridges and voles. People also wandered in these places though their number was comparable with partridges or rams. They were surrounded with dense vegetation: willows, asters, cordite, a wormwood, various cereals (for example, fescue) and a sedge. 
As to microflora structure also it it has appeared to distinguish probably from modern pollution and to define structure. However not the structure microbiota interested scientists, and that, how much ancient microbes were capable to resist to antibiotics. 
To answer this question, scientists have revealed those sites which provide now resistance to medicines from frozen DNA. They have revealed the genes providing stability to tetracycline and vancomycin, to penicillin and streptogramins. So, now stability enterococcal activators to vancomycin is provided with work difficult operon, including both genes-regulators, and genes of the enzymes changing a configuration of trailer communications peptides. 
In ancient tests there were genes of all these enzymes: both vanH, and vanA, and vanX. Naturally, they were not completely identical to modern analogues, but on a phylogenetic tree took of an intermediate position between that are found among modern bacteria. Scientists synthesised corresponding enzymes, being guided by the reconstructed sequence vanA. Its tertiary and quaternarythe structure, important just for execution of the protective role, has appeared same, as at modern enzyme.

  In strains of enterococci terminal dipeptide changes its chemical structure and is no longer bind to vancomycin, form resistant strains. This replacement is made at the expense of a specific set of the genes which are carrying out, as far as it is known, only this function. The scheme from article: S. V.Sidorenko  , V.I.Tishkov  . Molecular bases of resistance to antibiotics  (PDF, 1,4 Mb) //Successes of biological chemistry. Т. 44. With. 263–306

 Operon, providing resistance to vancomycin: vanR and vanS — regulators of an expression of genes of three enzymes — vanH, vanA and vanX; their co-ordinated work leads to replacement D-Ala on D-lac. The scheme from article: S. V.Sidorenko  , V.I.Tishkov  . Molecular bases of resistance to antibiotics  (PDF, 1,4 Mb) //Successes of biological chemistry. Т. 44. With. 263–306

Scientists have underlined that their work absolutely unequivocally specifies in resistance existence to antibiotics even before their wide introduction in human use. Antibiotics direct selection, and as a material for it the genetic variety turned out in the millenia serves.
Source: Vanessa M. D’Costa, Christine E. King, Lindsay Kalan, Mariya Morar, Wilson W. L. Sung, Carsten Schwarz, Duane Froese, Grant Zazula, Fabrice Calmels, Regis Debruyne, G. Brian Golding, Hendrik N. Poinar, Gerard D. Wright. Antibiotic resistance is ancient  //Nature. 22 September 2011 V. 477. P. 457–461.

No comments:

Post a Comment