Abundance and Taxonomic Diversity of Prokaryotes in Fluvisol and Associated Substrates (Vietnam, Pu Hoat Reserve)

The quantitative and qualitative characteristics are given of the soil prokaryotic communities in the Dystric Fluvisol, litter, and “suspended soil” in epiphyte baskets. The number of bacteria (direct luminescence method) varied from 1.1 to 2.6 billion cells/g soil and was the highest in the suspended soil sample and lower in the litter and A and AB horizons of Dystric Fluvisol (brown meadow alluvial soil). Proteobacteria, Actinobacteria, and Acidobacteria predominated in the prokaryotic community (at the phylum level); Chloroflexi, Firmicutes, and Verrucomicrobia were found in smaller amounts; the content of Nitrospirae, Planctomycetes, and Gemmatimonadetes was even lower. Representatives of the Archaea domain were found in the A horizon and in the suspended soil. Their content was significantly lower than that of the Bacteria domain and did not exceed 1%. Archaea were represented by the Thaumarchaeota and Euryarchaeota phyla in the A horizon and by Thaumarchaeota and Woesearchaeota phyla in the suspended soil. Based on the calculated ecological indices (alpha and beta diversity, measures of similarity by Bray-Curtis metrics and weighted UniFrac), it was shown that the microbiome of the suspended soil was closer to the microbiome of A horizon of Dystric Fluvisol than to the microbiome of litter. The metabolically active part of the prokaryotic community represented by the Proteobacteria, Actinobacteria, and Acidobacteria phyla reached its maximum in the suspended soil and was lower in the litter and A horizon of Dystric Fluvisol, and this correlated with the high abundance of these phyla and the significant taxonomic diversity of bacteria in this locus. Functional genes ( nifH and alkB ) were detected in all studied substrates. The number of copies of functional genes was the highest in the suspended soil sample, which makes this locus promising for isolating the strains with high biotechnological potential.