Selection and isolation of bacteria capable of degrading dinoseb (2-sec-butyl-4,6-dinitrophenol)

Abstract

Dinoseb (2-sec-butyl-4,6-dinitrophenol) has been a widely used herbicide that persists in some contaminated soils, and has been found in groundwaters, causing health and environmental hazards. Persistence in some soils may stem from a lack of dinoseb-degrading organisms. We established a chemostat environment that was strongly selective for aerobic (liquid phase) and anaerobic (sediment phase) bacteria able to degrade dinoseb. The chemostat yielded five taxonomically diverse aerobic isolates that could transform dinoseb to reduced products under microaerophilic or denitrifying conditions, but these organisms were unable to degrade the entire dinoseb molecule, and the transformed products formed multimeric material. The chemostat also yielded an anaerobic consortium of bacteria that could completely degrade dinoseb to acetate and CO2 when the Eh of the medium was less than -200 mV. The consortium contained at least three morphologically different bacterial species. HPLC analysis indicated that dinoseb was degraded sequentially via several as yet unidentified products. Degradation of these intermediates was inhibited by addition of bromoethane sulfonic acid. GC-MS analysis of metabolites in culture medium suggested that regiospecific attacks occurred non-sequentially on both the nitro groups and the side-chains of dinoseb. The consortium was also able to degrade 4,6-dinitro-o-cresol, 3,5-dinitrobenzoic acid, 2,4-dinitrotoluene, and 2,6-dinitrotoluene via a similar series of intermediate products. The consortium was not able to degrade 2,4-dinitrophenol. To our knowledge, this is the first report of strictly anaerobic biodegradation of an aromatic compound containing a multicarbon, saturated hydrocarbon side chain.