# Microbiomes of Primary Soils and Mining Heaps of Polymetallic Ore Quarries
## 4 Discussion
### Soil Microbiomes  
The representatives of Actinobacteria and Proteobacteria were dominant in taxonomy composition, which is typical of most bacterial soil communities [62; 63]. A notable proportion of Acidobacteria and Bacteroidetes was also found in each sample. The samples obtained from the primary soil formation sites in the Kulurtau and Tubinsky quarries were distinguished by a very small proportion of Verrucomicrobia and Thaumarchaeota phylum (less than 2%). Their content in the microbial community of the other samples varied for Verrucomicrobia from 5-6% (for the background soils of the Tuba-Kain pit dumps) to 20-22% (for the background soils of the Tubinsky pit) and from 10-15% of Thaumarchaeota. In spite of the poor study of Verrucomicrobia, these bacteria tend to dominate in many soil communities [64], and representatives of the archaea Thaumarchaeota are not only widely distributed in nature but also participate in nitrification, prevailing among ammonium-oxidizing soil microorganisms [65]. Consequently, the absence of suchimportant representatives of the microbial community in the forming soils of quarries indicates their underdevelopment and being at the initial stage of formation of a stable microbiome. Samples from the Kuliurtau and Tubinsky quarries had the highest number of minor types, the number of representatives of each of which did not exceed 2%. The dumps from the Tuba-Kain and Semenovsky quarries had a high similarity of microbial composition with the corresponding background soils, which was probably due to the relatively short age of abandonment since the end of mining at these sites (5-7 years and 1-2 years, respectively), during which the residual natural communities had not had time to degrade significantly. At the same time, an increase in the proportion of Bacteroidetes and a decrease in the number of Actinobacteria were observed in all the samples taken from areas with technological disturbed soils compared to the background. The high proportion of Actinobacteria phylum representatives in the samples is due to their wide distribution in the soils of arid regions with a neutral or alkaline environmental reaction [66]. However, it is also known that Actinobacteria play an important role in the decomposition of organic matter and take part in the carbon cycle [62]. Thus, when the amount of organic carbon decreases, their share in the microbial community decreases, which was observed for the samples of the studied quarry material. On the other hand, there was an increase in the proportion of representatives of Bacteroidetes, which also participate in the soil carbon cycle but thrive under more unfavorable environmental conditions, which is confirmed by the ubiquitous distribution of this phylum in all the studied ecosystems, especially in soils and human and animal intestines [67]. For the fine earth of the Tubinsky quarry, a significant increase in the number of Chloroleci representatives, which are mixotrophs and facultative anaerobes fixing carbon as a result of a special 3-hydroxypropionate cycle, was also observed compared to the control. These microorganisms are confined to hydromorphic soils with a rather low content of organic matter and a high content of soluble iron [68]. Judging by the agrochemical analysis of this sample, the organic carbon content in it was one of the lowest among the studied soils (1.4%); in addition, the sampling site was located in a lowland within the flooded part of the quarry, which could probably promote the development of relevant microorganisms. Representatives of the phylum Acidobacteria in the microbial community of all the studied samples had approximately similar amounts. Both the lowest and the highest proportions of these bacteria were observed in samples of natural undisturbed soils: the lowest at the background site of the Semenovsky pit dump (about 10-11%) and the highest at the background site of the Tubinsky pit (\(\approx\)20%).