The crystallization of calcium oxalates (weddellite and whewellite) by interaction of calcite marble with fungus Aspergillus niger, one of the most active stone destructors, was studied under in vitro conditions. The temporal development of acid production of fungus as well as the sequence of formation and morphogenesis of the growing oxalate hydrates crystals were investigated in detail. Furthermore, the relationships between morphology and growth conditions of crystals within the biofilms on the surface of carbonate rocks are discussed.

The composition of superficial deposits in urban environment and their importance in the development of the lithobiotic community of microorganisms has been investigated. Polyols, organic acids, mono- and disaccharides, as well as some amino acids, are the predominant low molecular weight organic components in superficial deposits, although the conditions on the stone surface are undoubtedly oligotrophic. Superficial deposits accumulate heavy metals, including Fe, Mn, Zn, Cu, Pb, and Cd, in surface sediments, among which the potentially toxic elements Zn, Cu, and Pb are accumulated in rather high concentrations. On model of Aspergillus niger as an example, it was shown micromycetes are resistant to heavy metals and retain their physiological activity when grown on this substrate. According to cultural studies, as well as metagenomic analysis, stress-resistant fungi and dark organotrophic bacteria are the main inhabitants of surface sediments. Probably, in the conditions of accumulation of superficial deposits on the stone, these organisms are the main inhabitants of the surface of the stone. With the development of more multi-species lithobiotic communities, they form the core of these communities. In the urban environment this type of primary colonization of the stone is likely realized.

Rock surfaces in natural systems are inhabited by multispecies communities of microorganisms. The biochemical activity of microorganisms and the patterns of microbial crystallization in these communities are mostly unexplored. Patterns of calcium carbonate and calcium oxalate crystallization induced by bacteria Bacillus subtilis and by B. subtilis together with Aspergillus niger on marble surface in vitro in liquid medium and in humidity chamber—were studied. Phase identification was supported by XRD, SEM, EDXS; metabolite composition was determined by GC–MS. It was found that the activity of B. subtilis–A. niger associations significantly differ from the activity of B. subtilis monocultures in the same trophic conditions. The phase composition and the morphology of the forming crystals are determined by the composition of the metabolites excreted by the microorganisms—particularly by the ratio of the concentrations of extracellular polymeric substances (EPS) and oxalic acid in the medium. The acidification activity of micromycetes may suppress the formation of bacterial EPS and prevent the formation of calcite. The present results can be used in the development of biotechnologies using microbial communities.

The present work contributes to the essential questions on calcium oxalate formation under the influence of lithobiont community organisms. We have discovered calcium oxalates in lichen thalli on surfaces of apatite-nepheline rocks of southeastern and southwestern titanite-apatite ore fields of the Khibiny peralkaline massif (Kola Peninsula, NW Russia) for the first time; investigated biofilm calcium oxalates with different methods (X-ray powder diffraction, scanning electron microscopy, and EDX analysis) and discussed morphogenetic patterns of its formation using results of model experiments. The influence of inorganic and organic components of the crystallization medium on the phase composition and morphology of oxalates has been analyzed. It was shown that, among the complex of factors controlling the patterns of biogenic oxalate formation, one of the main roles belongs to the metabolic activity of the lithobiont community organisms, which differs significantly from the activity of its individuals.

Microfungi were able to alternate solid substrate in various environments and play a noticeable role in the formation of insoluble calcium oxalate crystals in subaerial biofilms on rock surfaces. The present work describes how iron oxalate dihydrate humboldtine is acquired under the influence of the acid-producing microscopic fungus Aspergillus niger on the surface of two iron- bearing mineral substrates in vitro. Pyrrhotite and siderite rocks, as well as the products of their alteration, were investigated using a complex of analytical methods, including powder X-ray diffraction, optical microscopy, scanning electron microscopy and EDX spectroscopy. The effect of the underlying rocks with different composition and solubility and different oxidation states of iron on Fe-oxalate crystallization and on the morphology of humboldtine crystals was shown. The mechanisms of humboldtine formation were discussed. The results obtained in vitro seem promising for using fungi in bioleaching iron and other metals from processed ores and for the development of environmentally friendly biotechnologies.