Structural and Functional State of Microbial Communities of Ancient Soloids of Archaeological Monuments of the Black Sea Coast of Russia

A comprehensive assessment of the structural and functional state of microbial communities of multi-temporal buried ancient soloids (a soil-like formation similar to soil but without genetically formed horizons) in open archaeological pits of ancient human sites located in the middle reaches of the Mzymta River on the Sochi Black Sea coast in the Akhtsu Grotto and Akhshtyrskaya Cave was carried out. Changes in the functional biodiversity of ancient soloids compared to the background (alluvial soils that form in close proximity to the studied soloids and have similar mesomorphological properties) are noted: a decrease in the specific metabolic work (W) of microbial communities by 1.2 times according to the method of multisubstrate testing and an increase in the instability of paleomicrobial systems according to the index of the rank distribution of the spectra of consumption of substrates d > 1, which is typical for irreversibly damaged systems. The microbial community of ancient soloids has undergone a number of changes associated with anthropogenic activity. The analysis of the main absorption spectrum of substrates (MST method) showed that the microbial community of the soloid of the Akhtsu Grotto is oriented towards more intensive consumption of alcohols and amino acids, which suggests that organic matter of animal origin entered the cultural layer of the ancient human site. In the microbiome of the soloid of the Akhshtyrskaya cave the presence of lactotococci and bifidobacteria was found, which are extremely rare in soil and develop in conditions of excess carbohydrates on rich complex media, such as fermented meat and plant residues. Also, an increase in the content of keratinolytic fungi capable of decomposing keratin of hair, wool, feathers, etc. was found in the cultural layer of the cave site. Prokaryotic taxonomy in all the studied soils, with or without anthropogenic impact, was characterized by the predominance of the members of the Thermoleophilia clade and the families Gaiellaceae and Solirubrobacterales. Considering that these species require positive temperatures to develop, it suggests that the soils were formed in a mild climate. The Akhtsu grotto paleosols are a promising source of bacteria (genera Janthinobacterium, Lysobacter, Chitinophaga) that may have biotechnological potential.