Complete characterisation of Tn5530 from Burkholderia cepacia strain 2a (pIJB1) and studies of 2,4-dichlorophenoxyacetate uptake by the organism.
The complete genetic characterisation of Tn5530 in Burkholderia cepacia strain 2a (pIJB1) has been accomplished, indicating that it is a Tn3-like transposon with a complex structure bearing operons for the catabolism of 2,4-dichlorophenoxyacetate (2,4-D) and malonate. Tn5530 is terminated at both ends by the IS1071::IS1471 element and the 2,4-D- and malonate-dissimilatory operons are separated by a region encoding a putA and lrp gene and a gene encoding a chloride channel protein. The chloride channel protein may have a role in the expulsion of chloride ions liberated by the dissimilation of 2,4-D. In addition, a putative transposase with a high level of sequence similarity to those of plasmid pGH1 from Xanthomonas campestris pv. vesicatoria and Pseudomonas syringae pv. glycinea, and a transcription factor similar to those of the TetR family with low but significant levels of sequence similarity to those identified in a number of other organisms was observed. The entire Tn5530 sequence length, including the IS1071::IS1471 elements, was found to be 40,956bp, and pIJB1 was replicon-typed and otherwise characterised as being of the IncP-1beta subgroup, bearing merA and merD genes conferring resistance to mercuric chloride. The rate of uptake of 2,4-D by B. cepacia strain 2a was observed to proceed more readily at acid pH, suggesting involvement of the undissociated form of the compound. Uptake did not show saturation kinetics, was concentration-dependent, and appeared to occur in two stages; an initial accumulation followed by a linear second phase. Uptake could be inhibited by sodium azide but not by arsenate, N,N(')-dicyclohexylcarbodi-imide (DCCD) or carbonylcyanide m-chlorophenyl-hydrazone (CCCP) suggesting that it is not energy-dependent.
Norwood Laboratory, School of Chemical and Life Sciences, University of Greenwich, Wellington St., London SE18 6PF, UK.
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Bruce
D015084:2,4-Dichlorophenoxyacetic Acid / Q000493:pharmacokinetics*; D001483:Base Sequence; D001692:Biological Transport; D016956:Burkholderia cepacia / Q000235:genetics* / Q000378:metabolism*; D004251:DNA Transposable Elements; D004269:DNA, Bacterial / Q000737:chemistry*; D007700:Kinetics
D004251:DNA Transposable Elements; D004269:DNA, Bacterial; D015084:2,4-Dichlorophenoxyacetic Acid