Under conditions of carbon starvation or thermal, osmotic, or oxidative shock, mutants affected in the synthesis or mobilization of poly-3-hydroxybutyrate (PHB) are known to survive less well. It is still unclear if the synthesis and accumulation of PHB are sufficient to protect bacteria against stress conditions or if the stored PHB has to be mobilized. Here, we demonstrated that mobilization of PHB in Herbaspirillum seropedicae SmR1 was heat-shock activated at 45°C. In situ proton (¹H) nuclear magnetic resonance spectroscopy (i.e., ¹H-nuclear magnetic resonance) showed that heat shock increased amounts of 3-hydroxybutyrate (3HB) only in H. seropedicae strains able to synthesize and mobilize PHB. H. seropedicae SmR1 mutants unable to synthesize or mobilize PHB were more susceptible to heat shock and survived less well than the parental strain. When 100 mM 3-hydroxybutyrate was added to the medium, the ΔphaC1 strain (an H. seropedicae mutant unable to synthesize PHB) and the double mutant with deletion of both phaZ1 and phaZ2 (i.e., ΔphaZ1.2) (unable to mobilize PHB) showed partial rescue of heat adaptability (from 0% survival without 3HB to 40% of the initial viable population). Addition of 200 mM 3HB before the imposition of heat shock reduced protein aggregation to 15% in the ΔphaC1 mutant and 12% in the ΔphaZ1.2 mutant. We conclude that H. seropedicae SmR1 is naturally protected by 3HB released by PHB mobilization, while mutants unable to generate large amounts of 3HB under heat shock conditions are less able to cope with heat damage.

中文翻译：

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衍生自聚-3-羟基丁酸酯的3-羟基丁酸酯可减轻热胁迫的草螺旋藻SmR1中的蛋白质聚集。

在碳饥饿或热，渗透或氧化休克的条件下，已知在聚3-羟基丁酸酯（PHB）的合成或动员中受影响的突变体存活较差。尚不清楚PHB的合成和积累是否足以保护细菌免受胁迫，或者是否必须动员储存的PHB。在这里，我们证明了在45°C时热激激活了草螺旋藻SmR1中的PHB动员。原位质子（¹ H）核磁共振波谱（即¹ H核磁共振）显示，热激仅在能够合成和动员PHB的猪油状螺旋体菌株中增加了3-羟基丁酸酯（3HB）的量。不能合成或动员PHB的H. seropedicae SmR1突变体比亲本菌株更容易受到热休克的影响，并且存活得较差。当将100 mM 3-羟基丁酸酯添加到培养基中时，ΔphaC1菌株（无法合成PHB的嗜血丝球菌突变体）和具有phaZ1和phaZ2均缺失的双重突变体（即ΔphaZ1.2）（无法动员） PHB）显示部分挽救了热适应性（从没有3HB的0％存活率到初始可行种群的40％）。热休克减少蛋白质聚集的拼版到15％，在Δ之前的200mM 3HB的加成phaC1突变体和12％的Δ phaZ1.2突变体。我们得出的结论是，猪血清双歧杆菌SmR1受PHB动员释放的3HB天然保护，而在热休克条件下无法生成大量3HB的突变体则较不能应对热损伤。