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Increasing pollution of environment by toxic metals is the urgent problem requiring effective solution worldwide. The goal of the work was to study the dynamics of the interaction of Cr(VI), Mo(VI), W(VI) compounds with obligate anaerobic microorganisms Clostridium butyricum GMP1, which ferment organic compounds with the synthesis of hydrogen. The standard methods were used to determine рН and redox potential (Eh), the gas composition, and the concentration of metals. The application Clostridium butyricum GMP1 was showed to be useful to investigate its interaction with toxic metals. The higher redox potential of metal provided the opportunity for its faster and more effective reduction. The patterns of the reduction of toxic metals Cr(VI), Mo(VI) and W(VI) by obligate anaerobic strain Clostridium butyricum GMP1 were obtained. The experimental data confirmed the thermodynamically calculated correlation between the redox potential of the metal reduction to insoluble form and effectiveness of its removal. Obtained results can serve as the basis for further optimization and development of environmental biotechnologies for wastewater treatment with the simultaneous destruction of solid organic waste and hydrogen synthesis.

Chromium(VI) is one of the most hazardous contaminant of the water and soil environment. Thermodynamic calculations enable to determine the optimal metabolic pathways for microbial extraction of toxic soluble hexavalent chromium compounds from contaminated sewage. The purpose of this research was to predict theoretically and confirm experimentally the possibility of hazardous chromium(VI) removal by hydrogen producing microbiome with simultaneous destruction of multicomponent organic waste and hydrogen synthesis. Gas composition was determined by the standard gas chromatography method. The redox potential (Eh) and рН of the medium were measured potentiometrically by EZODO MP-103 universal ionomer. The Cr(VI) concentration was determined by a photocolorimetric method with 1,5-diphenylcarbazide (DFK). Multicomponent organic waste was effectively destroyed by hydrogen producing microbiome in control conditions (at the absence of chromium). Maximum concentration of H2 was 36% and biohydrogen yield was 81 l/kg of absolutely dry weight of waste. The weight of organic waste was 92 times decreased (Kd=92) during only 82 hours. The hydrogen fermentation cycle was not significantly inhibited by addition of Cr(VI). Thus, the efficiency of waste destruction and biohydrogen yield decreased consequently on 10% (Kd=83) and 7% (75 l/kg of waste) after addition of 50 ppm Cr(VI) to the culture liquid at the beginning of the final phase (50 hours) of the fermentation. As it was expected, the addition of 100 ppm Cr(VI) into the liquid phase during the final fermentation phase (80 hours) caused rapid increase of the redox potential and short-term inhibition of the fermentation process. However, after complete reduction of soluble CrO42- to insoluble Cr(OH)3∙nH2O↓ by hydrogen producing microorganisms, H2 synthesis resumed and metabolic parameters returned to initial values (the Eh was -185 mV and -99 mV after complete extraction of 50 ppm and 100 ppm Cr(VI) consequently). The optimal pathway of microbial detoxification of toxic chromium(VI) compounds was thermodynamically predicted and experimentally confirmed. High efficiency of CrO42- removal by strict anaerobic hydrogen producing microbiome via dark hydrogen fermentation of multicomponent organic waste was demonstrated. The obtained results could be used as the basis for development of novel environmental biotechnology of chromium-containing sewage purification and simultaneous destruction of environmentally hazardous organic waste as well as obtaining of eco-friendly energy carrier – biohydrogen.

Целью работы был количественный учет железовосстанавливающих бактерий в природных экосистемах Антарктики, Арктики, Мертвого и Черного морей, средних широт (Украина, Абхазия) и экваториальной зоны (Эквадор). Использованы метод количественного учета микроорганизмов по Мак-Креди, колориметрический метод определения соединений Fe(II) в культуральной жидкости. Впервые проведено системное исследование численности железовосстанавливающих бактерий обоих полушарий в экосистемах шести географических областей. Экспериментально показана высокая численность железовосстанавливающих бактерий в природных экосистемах. Их количество составило от 1,1·102 до 2,8·107 кл/г абсолютно сухого образца. Представленные результаты свидетельствуют о том, что железовосстанавливающие бактерии являются неотъемлемой составляющей природных экосистем и могут существенно влиять на биогеохимические циклы трансформации соединений железа и углерода., The aim of the work was quantitative determination of Fe(III)-reducing bacteria in natural ecosystems of the Antarctic, the Arctic, the Dead and the Black Sea, middle latitude (Ukraine, Abkhazia) and the equatorial zone (Ecuador). It was used the method of quantitative determination of microorganisms by McCready and the colorimetric method for determination of Fe(II) compounds . Results. The systemic study of the number of Fe(III)-reducing bacteria of both hemispheres in the ecosystems of six geographic regions was carried out for the first time. High number of Fe(III)-reducing bacteria in natural ecosystems was experimentally shown. The number of Fe(III)-reducing bacteria ranged from 1.1•102 to 2.8•107 cells/g of absolutely dry sample. Conclusions. The presented data showed that Fe(III)-reducing bacteria are an integral part of natural ecosystems and can significantly affect the biogeochemical cycles of iron and carbon compounds transformation.

The focus of the study was interaction of Candida tropicalis RomCu5 isolated from highland Ecuador ecosystem with soluble and insoluble copper compounds. Strain C. tropicalis RomCu5 was cultured in a liquid medium of Hiss in the presence of soluble (copper citrate and CuCl2) and insoluble (CuO and CuCO3) copper compounds. The biomass growth was determined by change in optical density of culture liquid, composition of the gas phase was measured on gas chromatograph, redox potential and pH of the culture fluid was defined potentiometrically. The concentration of soluble copper compounds was determined colorimetrically. Maximal permissible concentration of Cu2+ for C. tropicalis RomCu5 was 30 000 ppm of Cu2+ in form of copper citrate and 500 ppm of Cu2+ in form of CuCl2. C. tropicalis was metabolically active at super high concentrations of Cu2+, despite the inhibitory effect of Cu2+. C. tropicalis immobilized Cu2+ in the form of copper citrate and CuCl2 by it accumulation in the biomass. Due to medium acidification C. tropicalis dissolved CuO and CuCO3. High resistance of C. tropicalis to Cu2+ and ability to interact with soluble and insoluble copper compounds makes it biotechnologically perspective.

The aim of the study was regulation of metabolism of Citrobacter freundii Ml-31.1/1 on the basis of thermodynamic calculations. The essence of metabolism regulation was in ability to perform two opposite processes, namely mobilization and immobilization of iron compounds, depending on the culture conditions by single strain C. freundii Ml-31.1/1. The following methods were used: potentiometric measuring of pH and Eh values, colorimetric determination of microbial biomass increase and changes of iron compounds concentration, gas chromatography. The possibility of theoretically grounded regulation of iron transformation pathways was experimentally confirmed. Single culture (C. freundii Ml-31.1/1) provided both immobilization and mobilization of iron compounds due to specific conditions for microbial growth in nutrient medium.. Obtained regularities are the basis for assessing the role of microorganisms in iron biogeochemical cycles. This data could be used as a basis of effective biotechnologies of iron extraction from depleted deposits and water purification from iron compounds.