Induction of enzymes of 2,4-dichlorophenoxyacetate degradation in Burkholderia cepacia 2a and toxicity of metabolic intermediates

Abstract

Burkholderia cepacia 2a inducibly degraded 2,4-dichlorophenoxyacetate (2,4-D) sequentially via 2,4-dichlorophenol, 3,5-dichlorocatechol, 2,4-dichloromuconate, 2-chloromuconolactone and 2-chloromaleylacetate. Cells grown on nutrient agar or broth grew on 2,4-D-salts only if first passaged on 4-hydroxybenzoate- or succinate-salts agar. Buffered suspensions of 4-hydroxybenzoate-grown cells did not adapt to 2,4-D or 3,5-dichlorocatechol, but responded to 2,4-dichlorophenol at concentrations <0.4 mM. Uptake of 2,4-dichlorophenol by non-induced cells displayed a type S (cooperative uptake) uptake isotherm in which the accelerated uptake of the phenol began before the equivalent of a surface monolayer had been adsorbed, and growth inhibition corresponded with the acquisition of 2.2-fold excess of phenol required for the establishment of the monolayer. No evidence of saturation was seen even at 2 mM 2,4-dichlorophenol, possibly due to absorption by intracellular poly-beta-hydroxybutyrate inclusions. With increasing concentration, 2,4-dichlorophenol caused progressive cell membrane damage and, sequentially, leakage of intracellular K(+), P(i), ribose and material absorbing light at 260 nm (presumed nucleotide cofactors), until at 0.4 mM, protein synthesis and enzyme induction were forestalled. Growth of non-adapted cells was inhibited by 0.35 mM 2,4-dichlorophenol and 0.25 mM 3,5-dichlorocatechol; the corresponding minimum bacteriocidal concentrations were 0.45 and 0.35 mM. Strain 2a grew in chemostat culture on carbon-limited media containing 2,4-D, with an apparent growth yield coefficient of 0.23, and on 2,4-dichlorophenol. Growth on 3,5-dichlorocatechol did not occur without a supplement of succinate, probably due to accumulation of toxic quantities of quinonoid and polymerisation products. Cells grown on these compounds were active towards all three, but not when grown on other substrates. The enzymes of the pathway therefore appeared to be induced by 3,5-dichlorocatechol or some later metabolite. A possible reason is offered for the environmental persistence of 2,4,5-trichlorophenoxyacetic acid (2,4,5-T).

Effects of Selected Herbicides on Growth and Nitrogen Fixing Activity of Stenotrophomonas maltophilia (Sb16)

“…Adeleye et al (2004) studied the toxicity of 2, 4 D amine to Bacillus subtilis and found that a decrease in the survival percentage occurred at higher concen trations. Smith and Beadle (2008) also reported the toxi city of 2, 4 D and its metabolic intermediates on Burk holderia cepacia. The significant stimulation in the nitrogenase activity of Sb16 in lower concentrations of 2, 4 D in the present study corresponds to the find ings of Saikia et al (2014) who reported a higher rate of acetylene reduction in seedling roots of citronella ino culated with Azospirillum brasilense and treated with 2, 4 D than with A. brasilense alone.…”

Impact of Agrochemicals on Soil Microbiota and Management: A Review

“…Following the application, herbicides undergo physical and biochemical transformations and produce several secondary metabolites which are more lethal or persistent to non-target microbial communities. This is exemplified by the effect of 2,4-D and its metabolites on Burkholderiacepacia-a group of gram-negative bacteria [30]. The herbicidal action also depends on the type of formulation being used in addition to the active ingredient such as surfactant and solvent [18].…”

Bioremediation of pesticide-contaminated soil: a review on indispensable role of soil bacteria

“…(Iwaki et al, 2007). Smith and Beadle (2008) has also proven that B. cepacia has a 2,4-dichlorophenoxyacetate (2,4-D) degrading ability.…”