Govorukha V. Fe(III)-reducing microorganisms in biogeochemical cycles of carbon and iron

The thesis is dedicated to investigation of the role of Fe(III)-reducing microorganisms in biogeochemical cycles of carbon and iron and elucidation of regularities of microbial interaction with iron compounds. The pathways of microbial interaction with iron compounds were analyzed on the basis of thermodynamic calculations. Microorganisms were shown to carry out both iron mobilization and immobilization as well as reduction of Fe(III) to Fe(II). Systemic screening of ecosystems of Antarctic, Arctic, the Dead sea, the Black sea, middle latitude - Ukraine, Georgia, and equatorial region - Ecuador was conducted. Fe(III)-reducing microorganisms were shown to be widespread in ecosystems of both hemispheres of Earth at quantity from hundreds to tens of millions of cells per gram of sample. Moreover, the quantity of aerobic Fe(III)-reducing microorganisms was 10-100 times higher then anaerobic microorganisms. Effectiveness of microbial Fe(III)-reduction was from 5 to 78 %. Resistance of microorganisms of natural ecosystems to Fe(III) at the concentration 0,5-20 g/l was shown. Maximal permissible concentration of Fe(III) in liquid nutrient medium was 2-4 times higher then on agarized medium. The regularities of microbial Fe(III) reduction in the presence of competing terminal electron acceptors (О2 and NО3-) were studied. It is assumed that reduction of Fe(III) was non-specific due to the operation of nonspecific to Fe(III) redox enzymes. The regularities of Fe(III) compounds transformation by soil microorganisms were shown. The ability of microbial communities to maintain stability during the fermentation of substrate after addition of Fe(III) in concentration of 0,25 g/l can be used for modeling of their interaction with iron compounds. Effectiveness of Fe(III) reduction by pure cultures of microorganisms isolated in the presence of Fe(III) at the concentration from 0,5 to 20 g/l was established. Taxonomic position of the strains capable to reduce Fe(III) was established on the basis of their cultural, morphological, physiological and biochemical properties as well as phylogenetic analysis results. They were classified as Bacillus cereus, Bacillus thuringiensis, Citrobacter freundii, Pseudomonas mandelii, Pseudomonas panacis. The possibility of regulation of microbial metabolism for iron transformation was shown on the example of the strain Citrobacter freundii Ml-31.1/1. Mass-balance of reallocation of soluble and insoluble Fe(III) and Fe(II) compounds in culture liquid was obtained. High concentration of iron compounds in soil and water as well as widespread and high number of Fe(III)-reducing microorganisms and their resistance to Fe(III) at high concentration promote effective microbial interaction with iron compounds. This indicates significant influence of Fe(III)-reducing microorganisms on carbon and iron biogeochemical cycles. Obtained results can be used in prospect as a basis of novel environmental biotechnologies of water purification from iron compounds and increase of iron extraction from depleted deposits.