ИСТИНА

The goal of investigation is to determine the structure and diversity of different ecological and trophic groups of saprotrophic cultivated microorganisms (microscopic fungi, yeasts, bacteria) in different types of urban soils in field and in laboratory experiments. The main part of the investigation was held in a number of districts of megapolis - Moscow city, with the urban soils of different genesis, age, usage and ecological conditions (plant cover, types of pollutions, etc.). Some studies were carried out in small towns (Pushino, Serpukhov).It has been defined that the microbial communities of urban soils differ from those in natural soils in the same zonal conditions by the structure of microbial biomass, by taxonomic structure of saprotrophic microorganisms, by dominating species, by the increasing share of potentially pathogenic fungi, yeast and bacteria. Fungi are recognized as one of the most important groups of soil saprotrophic microorganisms, because of their leading role in decomposition of wide range of organic substances and high biomass content. It has been demonstrated by us that urban soils contain fungi primarily as a pool of spores. The mycelium content is considerably higher in soils of urban forests and parks (Terric Techniс Retisols, Albic Retisols), but less in the soils of residential areas (Urbic Technosols). The mycelial biomass varies depending on the seasons and may considerably grow up in urban soils as a result of application of remediation mixtures, wood chips, etc. Maximum content of viable fungal biomass has been revealed in summer in terms of fungal CO2 emission, as well as FDA hydrolysis. However, it was shown by the ergosterol extraction that the share of viable mycelium could be high also in winter and could be comparable to that in summer or even exceed it. The presence of small (filterable form) bacteria (<0,2 mkm) in the bacterial communities composition could be an indicator of their state . Electronic microscopy demonstrated that these bacteria are present in dormant form. The content of that bacteria are generally higher in urban than in natural soils. The distribution of microorganisms in urban soils is usually more mosaic than in natural soils. It is known, that pigmentation of organisms possesses the protective function concerning impact of some negative factors of the environment. It was defined that the share of the saprothrophic pigmented microorganisms in the urban soil could increase. The number of dark-colored melanin containing microfungi could increase in urban soils, exactly at the road-side zone. The third part of yeast species from urban soils has red-colored pigmentation, the most frequent are Cystofilobasidium capitatum, Cyst. macerans and Rhodotorula mucilaginosa. The tendency of increasing the pigmented forms was noted also for bacteria. Taxonomic diversity of cultivated microorganisms in urban soils also has its peculiar features, which depend from the soils properties. The lowest species diversity of cultivated microfungi has been noted in the long-term used urban soils and in the artificially composed urban soils, e.g., soil-like technogenic superficial formations. Compared to zonal soils, the mycobiota of urban soils is characterized by elevated levels of eurytopic microfungal species. Basidiomycetous yeast group is the most dominant in urban soil under the lawn vegetation in the city of Moscow. Except red-colored yeasts, this group contains wide spread species from genera Filobasidium, Naganishia, Papiliotrema, and some psychrophilic yeasts. Typical boreal soil yeast of genera Solicoccozyma and species Saitozyma podzolica are rarely isolated from urban soils. Different types of pollutions are an important factor for the formation of microbial communities in urban soils. For bacterial complexes it is manifested by the redistribution of taxa and increasing the abundance of bacteria adapted to certain types of pollution: namely, pigmented Rhodococcus to petroleum products, polychlorophenyls; Arhrobacter, Bacillus to heavy metals; Enterobacteriaceae to house hold pollutions. The prolonged soil (Urban Technosols) contamination with heavy metals and oil petroleum products did not significantly decrease the total number of bacteria, but somewhat reduced content of viable bacteria cells (to 55-60%) compared to the undisturbed natural soils (65-70%). The share of the small filterable forms of bacteria was 3-10 times more in urban soils polluted with heavy metals and oil petroleum. At the same time the microbial communities of urban soil could be more resistant to some stress factors than natural soil microbial communities. For example, the elevated soil temperatures affect assemblages of cultivated microfungi, changing their composition, diversity and microfungal communities compositions during the successions in laboratory experiments. The most pronounced effect of elevated temperatures (30 °C) on fungal diversity was revealed in the natural boreal soil (Umbric Albeluvisol) and the least pronounced in Urbic Technosol. A less pronounced response of microfungal assemblages to some stress factors in the urban soil in comparison with the natural soils may be due to a rather high species diversity as the result of the pronounced heterogeneity of their physicochemical properties and due to numerous sources of fungal spores input. It is known that in outdoor urban environment temperature is several degrees higher as compared to typical zonal temperatures. Thus, urban soil may include microbial species capable to growth at elevated temperatures. According to our data the share of microfungal species which are typical for areas situated southward, is increased in urban soils. There are some areas in the cities where the raise of soil temperatures could be expressed most strongly. Among of other anthropogenic factors, the influence of the elevated temperature on soil yeasts has not been studied previously. Our results has demonstrated that the temperature increase (for 5ºC) in urban soils located near the outdoor hot-water pipeline results in yeast abundance and species diversity. The number of yeast cells in soils under hot-water pipeline in winter season was 10 times higher and the taxonomic structure of yeast communities was more diverse (2.5 times) than in urban soils located at a distance. Thus, soils under warming impact are a favorable habitat for the soil yeast, and this anthropogenic factor leads also to increase of the mosaic of the microbial populations in urban soil. The type of urban management is of great importance for the urban microbiota formation. Structural alterations in the organic compounds introduced into urban soils brought the greater incidence of keratinolylic fungi and lower occurrence of cellulolytic fungi. Regular removal of leaf litter in autumn and introduction of remediation mixtures are leading to significant changes in microfungal species composition of urban soils, as well as affect rates and stage peculiarities of successions of cellulolytic fungi. Some microbial species in urban soil are recognized as dangerous for human health. The increasing of this potentially pathogenic (opportunistic) species in urban soils was recorded in the all groups of examined cultivated microorganisms. The accumulation in urban contaminated soil of the potentially pathogenic (many genera and species of the family Enterobacteriaceae), and allergenic bacteria (some species of the genus Rhodococcus and of Micrococcus) may constitute a threat to humans. The pathogenic and opportunistic yeast of species Candida albicans, C. glabrata, and C. parapsilosis were extracted from urban soils near garbage dumps. The most long-term investigations are carried out for the analysis of the presence of opportunistic microfungi in urban soils. Summarizing the results, we have observed the negative effect of the accumulation of potentially pathogenic species among all trophic groups of microfungi. The most frequent potentially pathogenic fungi registered in boreal urban soils of European part of Russia are: Aspergillus fumigatus, A.flavus, A.niger, Fusarium oxysporum, Scedosporium aurantiacum. The elevated soils temperature increase the presence of opportunistic fungi, as a rule. As it has been shown in our preliminary investigations, the botanical gardens could serve as the refugiums of natural groups of soil microorganisms in the urban areas. As a consequence, urban soil mycobiota develops specific features affecting the character of functioning of the soil organic complex, decomposition of organic substances, development of vegetation and thus contributing to the formation of the ecological image of urban ecosystems.