Kichise T, Fukui T, Yoshida Y, Doi Y
Department of Applied Chemistry, Faculty of Engineering, Toyo University, Saitama, Japan.
Int J Biol Macromol. 1999 Jun-Jul;25(1-3):69-77. doi: 10.1016/s0141-8130(99)00017-3.
Recombinant strains of Ralstonia eutropha PHB 4, which harbored Aeromonas caviae polyhydroxyalkanoates (PHA) biosynthesis genes under the control of a promoter for R. eutropha phb operon, were examined for PHA production from various alkanoic acids. The recombinants produced poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) [P(3HB-co-3HHx)] from hexanoate and octanoate, and poly(3-hydroxybutyrate-co-3-hydroxyvalerate-co-3-hydroxypentano ate) [P(3HB-co-3HV-co-3HHp)] from pentanoate and nonanoate. One of the recombinant strains, R. eutropha PHB 4/pJRDBB39d3 harboring ORF1 and PHA synthase gene of A. caviae (phaC(Ac)) accumulated copolyesters with much more 3HHx or 3HHp fraction than the other recombinant strains. To investigate the relationship between PHA synthase activity and in vivo PHA biosynthesis in R. eutropha, the PHB- 4 strains harboring pJRDBB39d13 or pJRDEE32d13 were used, in which the heterologous expression of phaC(Ac) was controlled by promoters for R. eutropha phb operon and A. caviae pha operon, respectively. The PHA contents and PHA accumulation rates were similar between the two recombinant strains in spite of the quite different levels of PHA synthase activity, indicating that the polymerization step is not the rate-determining one in PHA biosynthesis by R. eutropha. The molecular weights of poly(3-hydroxybutyrate) produced by the recombinant strains were also independent of the levels of PHA synthase activity. It has been suggested that a chain-transfer agent is generated in R. eutopha cells to regulate the chain length of polymers.
在真养产碱杆菌phb操纵子启动子的控制下，携带豚鼠气单胞菌聚羟基链烷酸酯（PHA）生物合成基因的重组菌株真养产碱杆菌PHB 4，被用于研究其从各种链烷酸生产PHA的情况。这些重组体从己酸和辛酸中产生聚（3-羟基丁酸酯-co-3-羟基己酸酯）[P(3HB-co-3HHx)]，并从戊酸和壬酸中产生聚（3-羟基丁酸酯-co-3-羟基戊酸酯-co-3-羟基戊酸酯）[P(3HB-co-3HV-co-3HHp)]。其中一个重组菌株，真养产碱杆菌PHB 4/pJRDBB39d3，携带豚鼠气单胞菌的ORF1和PHA合酶基因（phaC(Ac)），积累的共聚酯中3HHx或3HHp组分比其他重组菌株多得多。为了研究真养产碱杆菌中PHA合酶活性与体内PHA生物合成之间的关系，使用了携带pJRDBB39d13或pJRDEE32d13的PHB-4菌株，其中phaC(Ac)的异源表达分别由真养产碱杆菌phb操纵子和豚鼠气单胞菌pha操纵子的启动子控制。尽管PHA合酶活性水平差异很大，但这两个重组菌株之间的PHA含量和PHA积累速率相似，这表明聚合步骤不是真养产碱杆菌PHA生物合成中的限速步骤。重组菌株产生聚（3-羟基丁酸酯）的分子量也与PHA合酶活性水平无关。有人提出，真养产碱杆菌细胞中会产生一种链转移剂来调节聚合物的链长。
