Resistance of autochthonous soil bacteria to shock biocide effects

It was determined that bacteria in soils are characterized by a high resistance to short (1 day) treatments with saturated solutions of mineral salts, 96% ethanol, 1 N HCl, and 1 N NaOH. The soil treatment with acid and alkali did not cause any significant decrease of the bacteria number (staining with acridine orange) in the studied samples of alluvial meadow soil and ordinary chernozem; a significant amount of cells (10 to 30%) preserved the undisturbed structure of their DNA. The shock effects of the saturated salt solutions and ethanol on the bacteria were much weaker as compared with the acid and alkali treatments: 60 to 90% of the cells preserved an undisturbed structure of their DNA. The biocide treatments had significant effects on the number of saprotrophic bacteria grown on a glucose-peptone-yeast medium and manifested themselves in a decrease of the amount and taxonomic diversity, as well as in the essential rearrangement of the structure, of the saprotrophic bacterial complex: the absolute domination of bacilli and almost complete inhibiting of Gram-negative bacteria were observed. The proteobacteria and cytophagous bacteria appeared to be most sensitive to the biocide soil treatments; the bacteria of the actinomycetic line and bacilli were less sensitive. The cells resistant to the applied treatments were almost always found among the representatives of the Arthrobacter, Rhodococcus, Micrococcus, Myxococcus, and Polyangium genera.