The thermal resistance of fermenting microbes is a key characteristic of stable fermentation at high temperatures. Therefore, the effects of various metal ions on the growth of Zymomonas mobilis TISTR 548, a thermotolerant ethanologenic bacterium, at a critical high temperature (CHT) were examined. Addition of Mg2+ and K+ increased CHT by 1°C, but the effects of the addition of Mn2+, Ni2+, Co2+, Al3+, Fe3+, and Zn2+ on CHT were negligible. To understand the physiological functions associated with the addition of Mg2+ or K+, cell morphology, intracellular reactive oxygen species (ROS) level, and ethanol productivity were investigated at 39°C (i.e., above CHT). Cell elongation was repressed by Mg2+, but not by K+. Addition of both metals reduced intracellular ROS level, with only K+ showing the highest reduction strength, followed by both metals and only Mg2+. Additionally, ethanol productivity was recovered with the addition of both metals. Moreover, the addition of Mg2+ or K+ at a non-permissive temperature in 26 thermosensitive, single gene-disrupted mutants of Z. mobilis TISTR 548 revealed that several mutants showed metal ion-specific growth improvement. Remarkably, K+ repressed growth of two mutants. These results suggest that K+ and Mg2+ enhance cell growth at CHT via different mechanisms, which involve the maintenance of low intracellular ROS levels.

中文翻译：

---

耐热运动发酵单胞菌TISTR 548中金属离子的耐热性增强。

发酵微生物的耐热性是在高温下稳定发酵的关键特征。因此，研究了各种金属离子对耐热高温产乙醇细菌运动发酵单胞菌TISTR 548在临界高温（CHT）下生长的影响。Mg2 +和K +的添加使CHT增加1°C，但是Mn2 +，Ni2 +，Co2 +，Al3 +，Fe3 +和Zn2 +的添加对CHT的影响可以忽略不计。为了解与添加Mg2 +或K +相关的生理功能，在39°C（即高于CHT）下研究了细胞形态，细胞内活性氧（ROS）水平和乙醇生产率。Mg2 +抑制细胞伸长，但K +抑制细胞伸长。两种金属的加入都会降低细胞内ROS水平，只有K +表现出最高的还原强度，其次是金属和仅Mg2 +。另外，通过添加两种金属可以恢复乙醇的生产率。此外，在非允许温度下，在运动发酵单胞菌TISTR 548的26个热敏单基因破坏突变体中添加Mg2 +或K +时，发现几个突变体显示出金属离子特异性生长的改善。值得注意的是，K +抑制了两个突变体的生长。这些结果表明，K +和Mg2 +通过不同的机制增强CHT细胞的生长，这涉及维持低的细胞内ROS水平。mobilis TISTR 548揭示了几个突变体显示出金属离子特异性生长的改善。值得注意的是，K +抑制了两个突变体的生长。这些结果表明，K +和Mg2 +通过不同的机制增强CHT细胞的生长，这涉及维持低的细胞内ROS水平。mobilis TISTR 548揭示了几个突变体显示出金属离子特异性生长的改善。值得注意的是，K +抑制了两个突变体的生长。这些结果表明，K +和Mg2 +通过不同的机制增强CHT细胞的生长，这涉及维持低的细胞内ROS水平。