Structural and Functional State of the Microbial Communities in the Ancient Soloids of Archaeological Monuments on the Russian Black Sea Coast

Abstract

The structural and functional state of microbial communities of different-aged buried ancient soloids (soil-like bodies lacking genetically distinct horizons) have been comprehensively assessed in open archaeological pits of ancient human sites in the middle reaches of the Mzymta River on the Sochi Black Sea coast in the Akhtsu grotto and Akhshtyrskaya cave. A number of changes in the functional biodiversity of ancient soloids as compared with the background soils (alluvial soils formed immediately near the studied soloids with similar mesomorphological properties) are observed. They include a 1.2-fold decrease in the specific metabolic activity of microbial communities assessed by multisubstrate testing and an increased instability of paleomicrobial systems according to the coefficient of rank distribution of the range of substrate consumption d > 1, which is typical of irreversibly damaged systems. The microbial community of ancient soloids has undergone a number of changes associated with anthropogenic activity. According to the analysis of the main range of consumed substrates (multisubstrate testing), the microbial community of the Akhtsu grotto soloid displays a more intensive consumption of alcohols and amino acids, which suggests the supply of the organic matter of an animal origin to the cultural layer of ancient human site. Lactococci and bifidobacteria are identified in the Akhshtyrskaya cave soloid; they are extremely rare in soil and develop under conditions of excess carbohydrates on rich complex media, such as fermented meat and plant residues. In addition, an increased content of keratinolytic fungi capable of decomposing the keratin of hair, wool, feathers, and so on has been found in the cultural layer of the cave site. A comparative analysis of the prokaryotic taxonomy demonstrates the prevalence of the members of the Thermoleophilia class, family Gaiellaceae, order Solirubrobacterales in all the studied soils and soloids. These microorganisms require only positive temperatures for their development, suggesting a mild climate during the soil formation. The Akhtsu grotto paleosols are a promising source of bacteria (genera Janthinobacterium, Lysobacter, and Chitinophaga) that may possess biotechnological potential and useful properties.