Yang Mei Kwei, Lin Yu Chih, Shen Che Hung
Department of Life Science, Fu-Jen University, Taipei, Taiwan.
J Microbiol Immunol Infect. 2006 Feb;39(1):18-27.
Polyhydroxyalkanoates (PHAs), biopolyesters of hydroxyl fatty acids, are synthesized and deposited as cytoplasmic inclusions in many bacteria. We isolated a poly-beta-hydroxybutyrate (PHB)-producing bacterium designated Rhodobacter sphaeroides FJ1. To characterize PHB biosynthesis in this organism, we isolated the genes encoding proteins involved in PHB metabolism.
The genes responsible for the synthesis, accumulation, and degradation of PHB in R. sphaeroides FJ1 were cloned and characterized.
Genes involved in the biosynthesis and metabolism of PHB were found to be located in 2 different loci in the genome of R. sphaeroides FJ1. One locus contained genes encoding PHB depolymerase (phbZ), PHB synthase (phbC), phasin (phbP) and the regulator protein (phbR). The other locus contained the beta-ketothiolase gene (phbA) and the acetoactyl-CoA reductase gene (phbB). The phbZ gene was orientated in an opposite direction to that of phbC, phbP and phbR genes that were located in the same cluster. R. sphaeroides FJ1 was able to grow in wastewater released from the human waste treatment plant of Fu-Jen University. Optimal growth and PHB production were achieved when R. sphaeroides FJ1 was grown in tryptic soy broth containing 50% wastewater. PHB production by R. sphaeroides FJ1 varied in media with different carbon to nitrogen ratios, but the level of PHB synthase was constant, suggesting that PHB production depends mainly on substrate supply.
Six genes encoding proteins related to PHB metabolism are clustered in 2 separate loci, phbZCPR and phbAB, in a PHB-producing bacterium R. sphaeroides FJ1 isolated from wastewater. PHB synthase, the key enzyme for PHB synthesis, is constitutively expressed, and its expression level is not affected by different growth conditions.
聚羟基脂肪酸酯（PHA）是羟基脂肪酸的生物聚酯，在许多细菌中作为细胞质内含物合成并沉积。我们分离出一株产聚-β-羟基丁酸酯（PHB）的细菌，命名为球形红细菌FJ1。为了表征该生物体中PHB的生物合成，我们分离了编码参与PHB代谢的蛋白质的基因。
克隆并表征了球形红细菌FJ1中负责PHB合成、积累和降解的基因。
发现参与PHB生物合成和代谢的基因位于球形红细菌FJ1基因组的2个不同位点。一个位点包含编码PHB解聚酶（phbZ）、PHB合酶（phbC）、phasins蛋白（phbP）和调节蛋白（phbR）的基因。另一个位点包含β-酮硫解酶基因（phbA）和乙酰乙酰辅酶A还原酶基因（phbB）。phbZ基因的方向与位于同一簇中的phbC、phbP和phbR基因的方向相反。球形红细菌FJ1能够在辅仁大学人类污水处理厂排放的废水中生长。当球形红细菌FJ1在含有50%废水的胰蛋白胨大豆肉汤中生长时，可实现最佳生长和PHB产量。球形红细菌FJ1在不同碳氮比的培养基中PHB产量有所不同，但PHB合酶的水平是恒定的，这表明PHB产量主要取决于底物供应。
在从废水中分离出的产PHB细菌球形红细菌FJ1中，六个编码与PHB代谢相关蛋白质的基因聚集在两个独立的位点phbZCPR和phbAB中。PHB合酶是PHB合成的关键酶，其组成性表达，且其表达水平不受不同生长条件的影响。
