The turnover of medium-chain-length polyhydroxyalkanoates in Pseudomonas putida KT2442 and the fundamental role of PhaZ depolymerase for the metabolic balance
The turnover of medium-chain-length polyhydroxyalkanoates in Pseudomonas putida KT2442 and the fundamental role of PhaZ depolymerase for the metabolic balance
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DOI：
10.1111/j.1462-2920.2009.02061.x
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发表时间：
2010-01-01
影响因子：
5.1
通讯作者：
Prieto, Maria A.
中科院分区：
文献类型：
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作者：
Isabel de Eugenio, Laura;Escapa, Isabel F.;Prieto, Maria A.
P>聚羟基链烷酸酯 (PHA) 是由包括假单胞菌在内的多种细菌产生的可生物降解聚合物。当培养条件不平衡时，这些聚合物作为碳和能量储存材料积聚在细胞质中，因此，它们通常被认为在营养物质有限时充当碳和还原当量的汇。面临碳过剩和营养限制的细菌通过 PHA 聚合酶 (PhaC) 将多余的碳储存为 PHA。此后，在饥饿条件下，PHA解聚酶（PhaZ）降解PHA并释放R-羟基链烷酸，其可用作碳和能源。为了研究 PHA 代谢缺陷对恶臭假单胞菌 KT2442 生长的影响，我们构建了两个分别具有 PHA 聚合酶 (phaC1) 和 PHA 解聚酶 (phaZ) 编码基因缺陷的突变菌株。通过使用这些突变体，我们证明PHA在平衡储存的碳/生物量/细胞数量（作为碳可用性的函数）方面发挥着重要作用，这表明PHA代谢允许恶臭假单胞菌使羟酰辅酶A的碳通量适应细胞需求。此外，我们已经确定 PHA 合成和动员途径的协调在恶臭假单胞菌 KT2442 中配置了功能性 PHA 周转周期。最后，通过将 PHA 循环重定向至生物聚合物水解，设计出一种能够在细胞生长过程中向培养基中分泌对映体纯 R-羟基链烷酸的新菌株。
P>Polyhydroxyalkanoates (PHAs) are biodegradable polymers produced by a wide range of bacteria, including Pseudomonads. These polymers are accumulated in the cytoplasm as carbon and energy storage materials when culture conditions are unbalanced and hence, they have been classically considered to act as sinks for carbon and reducing equivalents when nutrients are limited. Bacteria facing carbon excess and nutrient limitation store the extra carbon as PHAs through the PHA polymerase (PhaC). Thereafter, under starvation conditions, PHA depolymerase (PhaZ) degrades PHA and releases R-hydroxyalkanoic acids, which can be used as carbon and energy sources. To study the influence of a deficient PHA metabolism in the growth of Pseudomonas putida KT2442 we have constructed two mutant strains defective in PHA polymerase (phaC1)- and PHA depolymerase (phaZ)-coding genes respectively. By using these mutants we have demonstrated that PHAs play a fundamental role in balancing the stored carbon/biomass/number of cells as function of carbon availability, suggesting that PHA metabolism allows P. putida to adapt the carbon flux of hydroxyacyl-CoAs to cellular demand. Furthermore, we have established that the coordination of PHA synthesis and mobilization pathways configures a functional PHA turnover cycle in P. putida KT2442. Finally, a new strain able to secrete enantiomerically pure R-hydroxyalkanoic acids to the culture medium during cell growth has been engineering by redirecting the PHA cycle to biopolymer hydrolysis.