Hying Zachary T, Rushmer Anya M, Loh Chin Yi, Bruger Eric L, Bazurto Jannell V
Department of Plant and Microbial Biology, University of Minnesota Twin Cities, St. Paul, Minnesota, United States of America.
Biotechnology Institute, University of Minnesota Twin Cities, St. Paul, Minnesota, United States of America.
PLoS Genet. 2025 Jun 9;21(6):e1011736. doi: 10.1371/journal.pgen.1011736. eCollection 2025 Jun.
Metabolic homeostasis is a central organizing principle of physiology whereby dynamic processes work to maintain a balanced internal state. Highly reactive essential metabolites are ideally maintained at equilibrium to prevent cellular damage. In the facultative methylotrophic bacterium Methylobacterium extorquens PA1, the utilization of one-carbon growth substrates, including methanol, generates formaldehyde as an obligate intermediate. Formaldehyde is highly chemically reactive and capable of damaging various biomolecules, making formaldehyde homeostasis critical during methylotrophic growth. However, homeostatic mechanisms that govern formaldehyde balance, which is readily perturbed upon transitioning to methylotrophic growth substrates, have remained elusive. Here we describe how a formaldehyde-sensing protein EfgA, a formaldehyde-responsive MarR-like regulator TtmR, and lanthanide-mediated methylotrophy together impact formaldehyde balance and one-carbon metabolism more broadly when cells are transitioning to growth on formaldehyde-generating one-carbon sources. We found that cells lacking efgA or ttmR are unable to maintain formaldehyde balance during various carbon source transitions resulting in elevated extracellular formaldehyde concentrations and an extended lag phase. In strains lacking efgA, we showed that inflated intracellular formaldehyde pools were accompanied by decreased cell viability, while the loss of ttmR resulted in the loss of one-carbon metabolites to the extracellular space. Additionally, we found less severe formaldehyde imbalances in the presence of lanthanides, even in the absence of efgA and ttmR. This was partly due to the activation of exaF, a lanthanide-dependent alcohol dehydrogenase that served as an alternative formaldehyde-detoxifying system that lessened the necessity of ttmR for maintaining formaldehyde homeostasis. Overall, our data demonstrated that efgA has a primary role in formaldehyde homeostasis in modulating intracellular formaldehyde pools, while ttmR is secondary, preventing carbon loss to the extracellular space. These results led us to develop a model of formaldehyde homeostasis involving formaldehyde sensing, growth arrest, compartmentalization, and auxiliary detoxification systems. This work deepens our understanding of how physiological factors impact biological formaldehyde homeostasis during transient metabolic imbalances of this universal cellular toxin.
代谢稳态是生理学的核心组织原则，通过动态过程来维持平衡的内部状态。高反应性必需代谢物理想情况下应保持平衡，以防止细胞损伤。在兼性甲基营养细菌甲基营养杆菌PA1中，包括甲醇在内的一碳生长底物的利用会产生甲醛作为必然中间体。甲醛具有高度化学反应性，能够损害各种生物分子，这使得甲醛稳态在甲基营养生长过程中至关重要。然而，控制甲醛平衡的稳态机制仍然难以捉摸，因为在向甲基营养生长底物转变时，甲醛平衡很容易受到干扰。在这里，我们描述了一种甲醛感应蛋白EfgA、一种甲醛响应的MarR样调节因子TtmR以及镧系元素介导的甲基营养如何在细胞向产生甲醛的一碳源生长转变时，更广泛地共同影响甲醛平衡和一碳代谢。我们发现，缺乏EfgA或TtmR的细胞在各种碳源转变过程中无法维持甲醛平衡，导致细胞外甲醛浓度升高和延迟期延长。在缺乏EfgA的菌株中，我们表明细胞内甲醛池膨胀伴随着细胞活力下降，而TtmR的缺失导致一碳代谢物向细胞外空间流失。此外，我们发现即使在没有EfgA和TtmR的情况下，镧系元素的存在也会导致较不严重的甲醛失衡。这部分是由于exaF的激活，exaF是一种镧系元素依赖性醇脱氢酶，作为一种替代的甲醛解毒系统，减少了TtmR维持甲醛稳态的必要性。总体而言，我们的数据表明EfgA在调节细胞内甲醛池中对甲醛稳态起主要作用，而TtmR是次要的，可防止碳向细胞外空间流失。这些结果使我们建立了一个涉及甲醛感应、生长停滞、区室化和辅助解毒系统的甲醛稳态模型。这项工作加深了我们对生理因素如何在这种普遍的细胞毒素的短暂代谢失衡期间影响生物甲醛稳态的理解。
