Russian researchers suggest using genetically modified coliform bacteria Escherichia coli with integrated gene from luminescent marine bacteria for as a simple test system for preliminary assessment of nanomaterials’ toxicity.

Nanomaterials seem to be present everywhere. Carbon nanoparticles enter atmosphere as products of methane, diesel duel and gasoline burning, and together with vehicle exhaust gases. Nanomaterials are promising tools for biology and medicine. However, a substance in the form of nanoparticles can be much more toxic than its “ordinary” state, and scientists know little about effects of nanomaterials on biological objects. Carbon nanotubes, for instance, are toxic for coliform bacteria.

In order to tell whether nanomaterials were toxic or not, researchers used Escherichia coli strain, which contained a gene from marine luminescent bacteria. Cell suspension was mixed with single-walled carbon nanotubes (these are particles with diameter between 0.7 to 2 nanometers), and in 1 milliliter of such solution contained 1 billion of bacterial cells and 0/2 milligrams of nanotubes. Then solution was incubated at room temperature for various periods of time. Carbon nanotubes were synthesized by arc technique in the laboratory of material spectroscopy of the Institute of General Physics. Then cells were washed from carbon particles and observed by means of atomic-force microscope.

 

 

Cells of Escherichia coli, which spent several days in water, look like normal rods. However, after 4 days of incubation of carbon nanotubes, surface of bacterial cells became deformed. Cells partly lost its contents, which leads to an easily detected visible cavity in its middle. After a week of incubation, cells totally lost their content, leaving empty deformed cell wall in the solution. Researchers say that carbon, from which nanotubes were made, never had such an effect on bacterial cells. Only nanotubes showed bactericidal properties, since after 2 days of incubation amount of living bacterial cells halved, and after 3 days – was 10 times less than in the beginning of the experiment. Well, carbon nanotubes seem to mechanically destroy bacterial cell wall and underlying membrane.

Apart from causing changes in appearance and reducing cell viability, carbon nanotubes also affect cell metabolism. After 1 hour of incubation with nanotubes bacteria start consuming twice as much oxygen, but get back to normal state by the end of 3^rd hour. Level of metabolism can be easily measured via cell luminescence: incubation with carbon nanotubes quenches luminescence of Escherichia coli cells with gene of marine luminescent bacteria.

Scientists found out that bioluminescence was tightly linked to cell viability. Measuring cell luminescence is quite simple, and express-analysis takes no longer than 30 minutes. Biochemical changes in bacterial cells start much earlier than changes in appearance can be detected. Luminescent bacteria, dried by a special technique, can be stored for months, making them a convenient test system for preliminary assessment of nanomaterials’ toxicity.

Source: Science & Technologies

Kizilova Anna