Biodegradation

, Volume 19, Issue 5, pp 669–681

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

Original Paper

DOI: 10.1007/s10532-007-9172-0

Cite this article as:
Smith, A.R.W. & Beadle, C.A. Biodegradation (2008) 19: 669. doi:10.1007/s10532-007-9172-0

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-β-hydroxybutyrate inclusions. With increasing concentration, 2,4-dichlorophenol caused progressive cell membrane damage and, sequentially, leakage of intracellular K+, Pi, 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).

Keywords

Burkholderia cepacia 2a Continuous culture 2,4-Dichlorophenol toxicity 2,4-Dichlorophenoxyacetate dissimilation Enzyme induction 

Abbreviations

2-CL

2-Chlorodienelactone

2-CM

2-Chloromaleylacetate

3,5-DCC

3,5-Dichlorocatechol

2,4-DCM

2,4-Dichloromuconate

2,4-DCP

2,4-Dichlorophenol

2,4-D

2,4-Dichlorophenoxyacetate

2,4,5-T

2,4,5-Trichlorophenoxyacetate

DMG

3,3′-Dimethylglutarate

4-HB

4-Hydroxybenzoate

α-KG

α-Ketoglutarate

MBC

Minimum bacteriocidal concentration

MCPA

4-Chloro-2-methylphenoxyacetate

MIC

Minimum inhibitory concentration

Pi

Inorganic phosphate

Copyright information

© Springer Science+Business Media B.V. 2008

Authors and Affiliations

  1. 1.Department of Life Sciences, School of Science University of GreenwichChatham MaritimeUK
  2. 2.School of Arts & Humanities Oxford Brookes UniversityGipsy Lane, OxfordUK

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