Many bacteria produce storage biopolymers that are mobilized under conditions of metabolic adaptation, for example, low nutrient availability and cellular stress. Polyhydroxyalkanoates are often found as carbon storage in Bacteria or Archaea, and of these polyhydroxybutyrate (PHB) is the most frequently occurring PHA type. Bacteria usually produce PHB upon availability of a carbon source and limitation of another essential nutrient. Therefore, it is widely believed that the function of PHB is to serve as a mobilizable carbon repository when bacteria face carbon limitation, supporting their survival. However, recent findings indicate that bacteria switch from PHB synthesis to mobilization under stress conditions such as thermal and oxidative shock. The mobilization products, 3-hydroxybutyrate and its oligomers, show a protective effect against protein aggregation and cellular damage caused by reactive oxygen species and heat shock. Thus, bacteria should have an environmental monitoring mechanism directly connected to the regulation of the PHB metabolism. Here, we review the current knowledge on PHB physiology together with a summary of recent findings on novel functions of PHB in stress resistance. Potential applications of these new functions are also presented.

中文翻译：

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PHB及其降解产物对细菌中应激状态的保护作用。

许多细菌产生的储藏生物聚合物在代谢适应的条件下动员，例如，低养分利用率和细胞应激。通常在细菌或古细菌中发现聚羟基链烷酸酯作为碳存储，其中这些聚羟基丁酸酯（PHB）是最常见的PHA类型。细菌通常在获得碳源并限制另一种基本营养素的情况下产生PHB。因此，人们普遍认为，当细菌面临碳限制时，PHB的功能是充当可移动的碳库，以支持其生存。但是，最近的发现表明，细菌在压力条件下（例如热和氧化性休克）从PHB合成转变为动员。动员产物3-羟基丁酸酯及其低聚物，对活性氧和热激引起的蛋白质聚集和细胞损伤具有保护作用。因此，细菌应具有与PHB代谢调节直接相关的环境监测机制。在这里，我们回顾了有关PHB生理学的最新知识，并总结了有关PHB在抗逆性方面的新功能的最新发现。还介绍了这些新功能的潜在应用。