Bacterial Stimulation by Carbamothioate Herbicides

Abstract

Laboratory studies enumerated butylate-, EPTC-, vernolate-, pebulate-, and cycloate-utilizing bacteria and actinomycetes in a Dothan loamy sand following repeated use of butylate, EPTC, or vernolate. Herbicide utilizers were isolated on a defined medium composed of minimal salts plus 200 mg/L herbicide as the primary carbon source plus 25 mg/L TTC as an indicator of organisms capable of metabolizing the herbicide substrates. Media inoculated with a butylate-history soil developed more TTC-red actinomycetes on the butylate-indicator agar than did media inoculated with a non-herbicide-history soil. Similarly, media inoculated with a vernolate-history soil developed more TTC-red bacteria on the vernolate-indicator agar. Cross-adaptation from vernolate to butylate and cycloate was evident, with inoculant from the vernolate-history soil exhibiting an increase in bacterial counts when butylate or cycloate was present as the primary carbon source. Likewise, previous butylate exposure corresponded with an increase in the number of vernolate- and pebulate-utilizing actinomycetes. Previous exposure to EPTC resulted in an increased population of butylate- and pebulate-utilizing actinomycetes.