Interfaculty Institute of Microbiology and Infection Medicine Tübingen, Eberhard-Karls-Universität Tübingen, Tübingen, Germany.
Wacker-Chair of Macromolecular Chemistry, TUM Department of Chemistry, Technical University of Munich, Munich, Germany.
Microb Cell Fact. 2020 Dec 22;19(1):231. doi: 10.1186/s12934-020-01491-1.
PHB (poly-hydroxy-butyrate) represents a promising bioplastic alternative with good biodegradation properties. Furthermore, PHB can be produced in a completely carbon-neutral fashion in the natural producer cyanobacterium Synechocystis sp. PCC 6803. This strain has been used as model system in past attempts to boost the intracellular production of PHB above ~ 15% per cell-dry-weight (CDW).
We have created a new strain that lacks the regulatory protein PirC (product of sll0944), which exhibits a higher activity of the phosphoglycerate mutase resulting in increased PHB pools under nutrient limiting conditions. To further improve the intracellular PHB content, two genes involved in PHB metabolism, phaA and phaB, from the known producer strain Cupriavidus necator, were introduced under the control of the strong promotor PpsbA2. The resulting strain, termed PPT1 (ΔpirC-REphaAB), produced high amounts of PHB under continuous light as well under a day-night regime. When grown in nitrogen and phosphorus depleted medium, the cells produced up to 63% per CDW. Upon the addition of acetate, the content was further increased to 81% per CDW. The produced polymer consists of pure PHB, which is highly isotactic.
The amounts of PHB achieved with PPT1 are the highest ever reported in any known cyanobacterium and demonstrate the potential of cyanobacteria for a sustainable, industrial production of PHB.
PHB（聚羟基丁酸酯）是一种很有前途的可生物降解的生物塑料替代品。此外，PHB 可以在天然产碳中性的蓝细菌集胞藻 PCC 6803 中完全以碳中性的方式生产。在过去提高 PHB 细胞内产量超过~15%的尝试中，该菌株被用作模型系统。
我们创造了一个新的菌株，它缺乏调节蛋白 PirC（sll0944 的产物），这导致在营养限制条件下磷酸甘油酸变位酶的活性增加，从而增加 PHB 池。为了进一步提高细胞内 PHB 含量，我们引入了两个参与 PHB 代谢的基因，phaA 和 phaB，来自已知的生产菌株铜绿假单胞菌，在强启动子 PpsbA2 的控制下。得到的菌株称为 PPT1（ΔpirC-REphaAB），在连续光照和昼夜光照条件下都能产生大量的 PHB。当在氮磷耗尽的培养基中生长时，细胞的 PHB 产量最高可达干重的 63%。添加乙酸后，PHB 含量进一步增加到干重的 81%。所产生的聚合物由纯 PHB 组成，具有高度的等规性。
PPT1 中 PHB 的含量是任何已知蓝细菌中最高的，这证明了蓝细菌在可持续、工业生产 PHB 方面的潜力。
