Pseudomonas extremaustralis is an Antarctic bacterium with high stress resistance, able to grow under cold conditions. It is capable to produce polyhydroxyalkanoates (PHAs) mainly as polyhydroxybutyrate (PHB) and, to a lesser extent, medium-chain length polyhydroxyalkanoates (mclPHAs). In this work, we analyzed the role of PHAs and cold adaptation in the survival of P. extremaustralis after lethal UVA exposure. P. extremaustralis presented higher radiation resistance under polymer accumulation conditions. This result was also observed in the derivative mutant strain PHA⁻, deficient for mclPHAs production. On the contrary, the PHB⁻ derivative mutant, deficient for PHB production, showed high sensitivity to UVA exposure. Complementation of the PHB⁻ strain restored the wild-type resistance level, indicating that the UVA-sensitive phenotype is due to the lack of PHB. All strains exhibited high sensitivity to radiation when cultured under PHAs non-accumulation conditions. A slight decrease in PHB content was observed after UVA exposure in association with increased survival. The scattering of UVA radiation by intracellular PHAs granules could also result in bacterial cell protection. In addition, cold conditions improved UVA tolerance, probably depending on PHB mobilization. Results showed that PHB accumulation is crucial in the resistance to UVA in P. extremaustralis. Mechanisms involved probably entail depolymerization and light scattering acting as a screen, both conferring protection against oxidative stress.

中文翻译：

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对南极细菌假单胞菌致死性UVA辐射的响应：聚羟基丁酸酯和冷适应作为保护因子

极端假单胞菌是一种具有高抗逆性的南极细菌，能够在寒冷条件下生长。它能够生产聚羟基链烷酸酯（PHA），主要是聚羟基丁酸酯（PHB），在较小程度上生产中链长度的聚羟基链烷酸酯（mclPHA）。在这项工作中，我们分析了致命的UVA暴露后，PHA和冷适应在极端疟原虫生存中的作用。在聚合物积累条件下，极度假单胞菌表现出较高的抗辐射性。该结果也被用在衍生突变株PHA观察^- ，缺陷的mclPHAs生产。相反，在PHB ^-缺乏PHB产生的衍生突变体显示出对UVA暴露的高度敏感性。该PHB的互补^-应变恢复了野生型阻力一级，表明UVA-敏感表型是由于缺乏PHB的。在PHA非积累条件下培养时，所有菌株均对辐射表现出高敏感性。暴露于UVA后，观察到PHB含量略有下降，这与存活率增加有关。细胞内PHA颗粒对UVA辐射的散射也可能导致细菌细胞保护。此外，寒冷的天气改善了对UVA的耐受性，这可能取决于动员PHB。结果表明，PHB积累对于极端疟原虫的抗UVA至关重要。。所涉及的机制可能需要解聚和充当屏幕的光散射，两者都可以提供针对氧化应激的保护。