Buried Soils as a New Source for Isolation of Biotechnologically Significant Bacterial Strains

Resumo

Investigation of molecular genetic diversity in paleosoil microbial communities revealed that ~50% of ancient ribotypes were not detected among the ribotypes of the modern microbial communities. Thus, reactivation of ancient microorganisms and investigation of their physiological properties as potentially valuable producers for biotechnology is advisable. The proteolytic bacterial component of paleosoils below burial mounds collected from the vials with votive food at the Peschanyi-4 and Netkachevo burial mounds (15–centuries BC) (Volgograd and Rostov oblasts, Russia) was investigated. Viable cell numbers of heterotrophic bacteria in reactivated samples were (1.5–16.0) × 10⁷ CFU/g soil (growth on LB agar). Using alternating inoculation into liquid media and plating on solid media resulted in isolation of pure cultures of several strains, which were then identified based on analysis of their 16S rRNA gene sequences. Strains of the following species were isolated: Bacillus coagulans (Lactobacillus coagulans), a potentially valuable probiotic; Aquamicrobium terrae, a proteolytic producing surfactants and degrading organic matter; Bacillus cereus, the strain toxicogenic for outbred white mice at intra-abdominal application; Staphylococcus hominis and St. epidermidis, opportunistic pathogens belonging to normal human skin microflora. Apart from Bacillus cereus, all strains exhibited high production of neuroactive amines (DOPA, DOPAC, DA, 5-HTP, HVA, and 3-MT) and amino acids (Asp, Glu, Gly, Tau, and GABA). The strains isolated from the vials with votive food were mostly those associated with humans, rather than typical members of soil microbial communities.