Ohtsubo Y, Nagata Y, Kimbara K, Takagi M, Ohta A
Department of Biotechnology, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, 113-8657, Tokyo, Japan.
Gene. 2000 Oct 3;256(1-2):223-8. doi: 10.1016/s0378-1119(00)00349-8.
The bph genes involved in PCB/biphenyl degradation in Pseudomonas sp. KKS102 are clustered as bphEGFA1A2A3BCDA4R. The bph genes are inducibly expressed in the presence of biphenyl. In order to understand the induction more fully, the inducer of bph gene expression was investigated. To identify the inducer molecule, we constructed four deletion mutants of the structural genes and analyzed the inducibility of the bphE gene in each mutant strain. In the wild-type cell and the bphD deletion mutant, the levels of the bphE transcript were enhanced in the presence of biphenyl. On the other hand, in the bphA, bphB, and bphC deletion mutants, levels of the bphE transcript were not enhanced in the presence of biphenyl. These results demonstrated that the series of reactions catalyzed by biphenyl dioxygenase (BphA), dihydrodiol dehydrogenase (BphB), and 2, 3-dihydroxybiphenyl dioxygenase (BphC) are necessary to convert biphenyl to the inducer. It is known that these reactions convert biphenyl to 2-hydroxy-6-oxo-6-phenylhexa-2,4-dienoic acid (HOPDA), and it was found that the expression of the bph genes was induced by purified HOPDA. These results clearly indicate that HOPDA is the inducer of the bph genes in KKS102.
假单胞菌属KKS102中参与多氯联苯/联苯降解的bph基因成簇排列为bphEGFA1A2A3BCDA4R。bph基因在联苯存在时可被诱导表达。为了更全面地了解这种诱导作用，对bph基因表达的诱导剂进行了研究。为了鉴定诱导剂分子，我们构建了结构基因的四个缺失突变体，并分析了每个突变株中bphE基因的可诱导性。在野生型细胞和bphD缺失突变体中，联苯存在时bphE转录本水平升高。另一方面，在bphA、bphB和bphC缺失突变体中，联苯存在时bphE转录本水平未升高。这些结果表明，由联苯双加氧酶（BphA）、二氢二醇脱氢酶（BphB）和2,3-二羟基联苯双加氧酶（BphC）催化的一系列反应对于将联苯转化为诱导剂是必要的。已知这些反应将联苯转化为2-羟基-6-氧代-6-苯基己-2,4-二烯酸（HOPDA），并且发现bph基因的表达由纯化的HOPDA诱导。这些结果清楚地表明，HOPDA是KKS102中bph基因的诱导剂。
