Bacteria

“In the XV century, people have learned how to get copper out of the blue streams, which flow from the mountains. But the mechanism of Vatting of non-ferrous metals from sulphide ores was understood much later, in the XX century, – says head of the Laboratory of the chemolithotrophs Microorganisms of the Institute of Microbiology named after S.N. Winogradsky Academy of Sciences Tamara Kondratieva to Infox.ru. – Chemolithotrophs acidophilic bacteria play the main role in this process.

They use ferrous iron, elemental sulfur and its reduced compounds as an energy source. This process is being conducted at values of pH 2-3, i.e. in a sufficiently acid medium, and in the temperature range 4-80 ° C. Among them there are mesophilic, i.e. the peak of activity of which is observed at 28-30 ° C, a moderately thermophilic, for which the optimum temperatures are 45-55 ° C, and thermophiles (heat lovers), it is mainly archaea, preferring to live in temperatures above 60 ° S.

There are generalists, which can oxidize all substrates. This is, for example, such a gram-negative bacterium Acidithiobacillus ferrooxidans. There are bacteria that can oxidize only iron or only sulfide component. All of these bacteria in natural ecosystems form communities. They are responsible for acidification of water bodies, pollution of heavy metal ions. Also, they destroy the sulfur deposits, turning them into sulfuric acid. That is, on the one hand, they bring harm to humans. And on the other hand – people have learned to use them for precious metals”.

“We are studying the physiology, morphology, genetics of these bacteria – continues Dr. Kondratyev. – In recent years, we have identified a new family of chemolithotrophs acidophilic archaea. Its representative – is a very interesting Archean, growing at a fairly low temperatures and oxidizes the iron, while the majority of these archaea oxidize sulfur. We also discovered several kinds of bacteria Sulfobacillus, for example Sulfobacillus sibiricus and Sulfobacillus olympiadicus.

Moreover, we have described them first, but now they are distinguished in different geographical areas, different substrates and different technological processes. Thus we have shown that species diversity is not very large, but very large strain diversity. We also describe the key factors responsible for this diversity. This is an energy substrate and the concentration of heavy metals.

When changing environmental factors, microorganisms begin to adapt to them. Typically, the changes are reversible, but in the case of irreversible changes in the structure of chromosomal DNA we can talk about the experimental getting of new strains. Non-permanent elements of the genome, such as plasmid – DNA molecules out of the chromosomes play the main role in the formation of new strains. Also, we are exploring the use of bacteria in hydro-bio-metallurgical technology that is improving the existing ones and creating new, cost-effective and environmentally safe ones”.

Technologies

“First, we need to study the metabolism of microorganisms in laboratory conditions – continued the candidate of biological sciences Anna Zhuravleva the story of Kondrateva to Infox.ru. – It helps to understand the behavior of the microbial community in certain concentrations of oxygen, temperature. Interesting properties of microorganisms are discovered: e.g., sulfobacillus, oxidizing sulfur and iron at high temperatures, evolutionarily developed the property to eat organic substrates.

“All the basic research being conducted in our laboratory, have important practical value – the doctor of science Natalia Fomchenko explained to Infox.ru. – Non-ferrous metals are extracted from sulphide ores by pyrometallurgical means, that is firing.

This entails a large amount of dust emission, sulfur dioxide and other greenhouse gases. Therefore an interest in hydrometallurgical processes increased worldwide. Particularly interesting are bio-hydro-metallurgical processes, i.e. the processes in the aquatic environment with the participation of microorganisms.

We propose the concept of two-stage bio-oxidation of sulphide concentrates containing non-ferrous metals and gold. The process is divided into chemical and biological stage, each of which creates optimal conditions for the processes.

In this configuration, it can compete with the pyrometallurgical not only according to the environmental but also economic indicators. The oxidant formed on the stage of bio-oxidation is directed to the stage of chemical leaching of the concentrates of sulfide ores.

It appears to be wasteless highly efficient process that allowed to obtain zinc and copper in the experimental conditions. For gold, this approach is also suitable. Previously gold in Russia was extracted from alluvial ore, but as their reserves were depleted, then the work goes with indigenous ores containing unoxidized sulfides. Bacteria can process ore, which can not be processed by any other technology”.