Long-term survivability is well-known for microorganisms in nutrient-depleted environments, but the damage accrued by proteins and the associated repair processes during the starvation and recovery phase of microbial life still remain enigmatic. We focused on aspartic acid (Asp) racemization and repair in the survival of Pyrococcus furiosus and Thermococcus litoralis under starvation conditions at high temperature. Despite the dramatic decrease of viability over time, 0.002% of P. furiosus cells (2.1×10³ cells/mL) and 0.23% of T. litoralis cells (2.3×10⁵ cells/mL) remained viable after 25 and 50 days, respectively. The D/L Asp ratio in the starved cells was approximately half of those from the autoclaved cells, suggesting that the starving cells were capable of partially repairing racemized Asp. Transcriptomic analyses of the recovered cells of T. litoralis indicated that the gene encoding Protein-L-isoaspartate (D-aspartate) O-methyltransferase (PIMT) might be involved in the repair of damaged proteins by converting D-Asp back to L-Asp during the resuscitation of starved cells. Collectively, our results provided evidence that Asp underwent racemization in the surviving hyperthermophilic cells under starved conditions and PIMT played a critical role in the repair of abnormal aspartyl residues during the initial recovery of starved, yet still viable, cells.

中文翻译：

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天冬氨酸消旋化和修复对高温长期饥饿后超嗜热菌的存活和恢复

众所周知，营养耗尽环境中的微生物具有长期生存能力，但在微生物生命的饥饿和恢复阶段，蛋白质和相关修复过程所产生的损害仍然是个谜。我们专注于天冬氨酸 (Asp) 消旋化和修复在高温饥饿条件下Pyrococcus furiosus和Thermococcus litoralis的存活。尽管存活率随时间急剧下降，0.002% 的P. furiosus细胞（2.1×10 ³细胞/mL）和 0.23% 的T. litoralis细胞（2.3×10 ⁵细胞/mL）分别在 25 天和 50 天后保持活力。饥饿细胞中的 D/L Asp 比率约为高压灭菌细胞的一半，表明饥饿细胞能够部分修复外消旋化的 Asp。对T. litoralis回收细胞的转录组学分析表明，编码蛋白-L-异天冬氨酸（D-天冬氨酸）O-甲基转移酶（PIMT）的基因可能通过将D-Asp 转化回L-Asp 参与受损蛋白质的修复在饥饿细胞复苏期间。总的来说，我们的结果提供了证据，证明 Asp 在饥饿条件下幸存的超嗜热细胞中发生外消旋化，而 PIMT 在饥饿但仍然存活的细胞的初始恢复过程中在修复异常天冬氨酰残基方面发挥了关键作用。