Application of phytobacterial communities for bioremediation of ecosystems

According to the materials of report at the meeting of the Presidium of the NAS of Ukraine, December 27, 2023

Abstract

Currently, the most powerful source of metal pollution is the hostilities taking place on the territory of Ukraine as a result of Russia’s full-scale invasion. Rocket, artillery and mortar attacks, as well as the activity of military equipment and aviation led to the accumulation of heavy metals in the soil and the degradation of agrocenoses. The development of effective methods of metals removal from polluted ecosystems is an urgent task of science and industry. The report deals with study of the concept of thermodynamic prognosis of the interaction of microorganisms and plants with metal compounds, microbial immobilization and mobilization of metals on the example of copper, accumulation of metals by phytoremediant plants and their anaerobic degradation with energy carriers production. The approach is based on the thermodynamic prognosis to substantiate the optimal pathway of microorganisms and plants interaction with metals. Thermodynamic prognosis was used to determine the conditions and products of the interaction of microorganisms and plants with metal compounds. According to the thermodynamic prognosis the types of interaction of microorganisms with metals (on the example of copper) were clarified. Microorganisms were able to accumulate Cu²⁺ in microbial cells as a result of replacing the macroelement Mg²⁺ (stereochemical analogy of metals and macroelements), precipitate copper compounds without changing their valence state, and reduce Cu²⁺ to the insoluble oxide of monovalent copper Cu₂O↓. The postulates of the thermodynamic prognosis were experimentally confirmed in laboratory conditions. Bacteria resistant to soluble Cu(II) compounds were isolated at the Department of Biology of Extremophilic Microorganisms of the D.K. Zabolotny Institute of Microbiology and Virology of the National Academy of Sciences of Ukraine. They were not only resistant to metals, but also interacted with them — accumulated in cells and reduced to insoluble and non-toxic oxide Cu₂O↓. Pseudomonas lactis UKR1 copper-resistant strain was studied. Strain was able to immobilize and mobilize copper compounds under the regulation of microbial metabolism. According to the thermodynamic prognosis, the most effective immobilization of metals should occur through reduction under conditions of significant difference between the donor (microorganisms) and acceptor (metal-oxidizer) systems. As a result, the most effective reduction of metals should be carried out by low-potential strict anaerobic microorganisms. This assumption was experimentally confirmed on the example of methanogenic microbial community. It was shown that the methanogenic microbial community completely (with 100% efficiency) immobilized copper during the anaerobic degradation of invasive plants biomass (water lettuce). The high efficiency of microbial degradation of phytoremediant plant biomass (grasses, tobacco, wormwood, nettle, ragweed, and goldenrod) with biogas synthesis has already been demonstrated at the Department of Biology of Extremophilic Microorganisms. Thus, the availability of development of combined environmental biotechnologies of bioremediation and phytoremediation of polluted ecosystems with simultaneous production of energy carriers — hydrogen and methane was theoretically substantiated and experimentally confirmed.