It was shown that Avercom and plant growths regulators act as weak mutagens on auxotrophic test-cultures Salmonella typhimurium TA 100 and TA 98. Their antimutagenic influence on test-cultures of Salmonella typhimurium TA 100 and TA 98 was studied. The addition of S. avermitilis UCM Ac-2177 biomass, cultural liquid and Avercom of different concentrations separately to soil increased the quantity of pedotrophic, amylolytic, phosphorus immobilizing and amonificating microbes.