Reactivation of dormant and nonculturable bacterial forms from paleosoils and subsoil permafrost

Methods of reactivating the dormant forms (DFs) and nonculturable cells (NCs) of the bacterial communities of buried paleosoils and subsoil permafrost stored for long periods of time (thousands to millions of years), including completely sterile samples (CFU = 0), were developed. They were based on washing the DFs and NCs to remove anabiosis autoinducers (spore germination autoinhibitors) and introducing low molecular weight extracellular growth regulators of microbial or plant origin, such as alkylhydroxybenzenes of the alkylresorcinol subtype, indoleacetic acid, and wheat germ agglutinin. It was revealed that the dormant communities of permafrost and buried soils differed in their sensitivity to reactivating factors, probably due to different natural storage conditions of the tested soil substrates and the heterogeneity of dormant populations. The latter was confirmed by FISH (fluorescent in situ hybridization): applying the reactivation methods to the cells of the dormant permafrost community resulted in an increase in the number of metabolically active cells from 5 to 77% of their total number. In contrast, the addition of microbial anabiosis autoinducers (C-12-AHB) to background surface soil and permafrost samples caused the transition of bacterial cells to the dormant or the nonculturable state, depending on the C-12-AHB concentration and the sensitivity of the cells from the control soil or permafrost' to it. The data obtained contribute to our knowledge concerning the role of intercellular communication factors and the survival of microorganisms under extreme environmental conditions.