降解2,4-二氯酚微生物的分离及其2,4-二氯酚羟化酶基因的克隆和表达

从土壤中分离到一株降解2,4-二氯酚能力较强的细菌菌株GT241-1，经鉴定该菌株属于假单胞菌属。菌株GT241-1在最适条件下能在48h内将90mg/L的2,4-DCP降解91%，能利用2,4-二氯酚、2,4-二氯苯氧乙酸、苯甲酸和儿茶酚为唯一碳源生长。采用Southern杂交对2,4-二氯酚羟化酶基因（dcpA）定位后构建基因组文库，再用斑点杂交筛选目的转化子，克隆了该菌株的dcpA。序列测定得知含dcpA的亚克隆片段全长2389bp，其中dcpA基因编码区1797bp。核苷酸和氨基酸序列分析表明，dcpA与已在GenBank登记的相关基因有一定的差异。dcpA基因能够在大肠杆菌转化子中成功地表达有生物活性的酶。

Isolation of 2,4-Dichlorophenol Degrading Bacterium Strain and Cloning and Expression of Its 2,4-dichlorophenol Hydroxylase Gene

2,4-Dichlorophenol is toxic and biorefratory organic pollutant. A 2,4-dichlorophenol degrading bacterial strain GT241-1, identified as Pseudomonas sp., was isolated from soil samples which was collected from drainage area of several 2,4-dichlorophenol producing factories. Strain GT241-1 had strong 2,4-dichlorophenol degrading ability, it could decompose 91% 2, 4-dichlorophenol of 90 mg/L within 48 hours at 25 - 30 degrees C, and could utilize 2,4-dichlorophenol, 2,4-dichlorophenoxyacetic acid (2,4-D), benzoate and catechol as sole carbon and energy source. Southern blot showed that 2,4-dichlorophenol hydroxylase gene (dcpA) of strain GT241-1 locates on the about 10kb EcoR I/Xba I fragment. This fragment was recovered, linked to the vecter pUC19 and transformed into the E. coli DH5alpha. A aim transformant, Z539, was obtained by dot blotting from about 1200 transformants. PCR and the sequencing results shew that the whole dcpA gene is contained within the 10kb EcoR I /Xba I fragment of pZ539. This fragment was shortened to about 2.4kb by HindmIII. The shorted fragment was subcloned to vecter pRSET-B to get a transformant BS1-12. The subcloned fragment was sequenced. Sequencing results showed that the whole length of the subcloned fragment containing dcpA is 2389bp and the nucleotide span of coding region is from number 276 to number 2072 (1797 bp), with ATG and TAA as start and stop codon respectively. The sequence analysis of dcpA and the deduced amino acid encoded by dcpA showed that they are different from the relative sequences registered in the GenBank. The subcloned fragment carry the promoter of dcpA, this can deduce from the fact that the upflow length of dcpA coding region is 275bp, and further confirmed by the 2,4-dichlorophenol hydroxylase activity measurement results. The 2,4-dichlorophenol hydroxylase activity of transformant Z539 and BS1-12 were detected, the results showed these transformants have 2,4-dichlorophenol hydroxylase activity. By comparison, the activity of these transformants were lower than that of the strain GT241-1.