Wehrmann Matthias, Billard Patrick, Martin-Meriadec Audrey, Zegeye Asfaw, Klebensberger Janosch
University of Stuttgart, Institute of Technical Biochemistry, Stuttgart, Germany.
Université de Lorraine, LIEC UMR7360, Faculté des Sciences et Technologies, Vandoeuvre-lès-Nancy, France.
mBio. 2017 Jun 27;8(3):e00570-17. doi: 10.1128/mBio.00570-17.
The oxidation of alcohols and aldehydes is crucial for detoxification and efficient catabolism of various volatile organic compounds (VOCs). Thus, many Gram-negative bacteria have evolved periplasmic oxidation systems based on pyrroloquinoline quinone-dependent alcohol dehydrogenases (PQQ-ADHs) that are often functionally redundant. Here we report the first description and characterization of a lanthanide-dependent PQQ-ADH (PedH) in a nonmethylotrophic bacterium based on the use of purified enzymes from the soil-dwelling model organism KT2440. PedH (PP_2679) exhibits enzyme activity on a range of substrates similar to that of its Ca-dependent counterpart PedE (PP_2674), including linear and aromatic primary and secondary alcohols, as well as aldehydes, but only in the presence of lanthanide ions, including La, Ce, Pr, Sm, or Nd Reporter assays revealed that PedH not only has a catalytic function but is also involved in the transcriptional regulation of and , most likely acting as a sensory module. Notably, the underlying regulatory network is responsive to as little as 1 to 10 nM lanthanum, a concentration assumed to be of ecological relevance. The present study further demonstrates that the PQQ-dependent oxidation system is crucial for efficient growth with a variety of volatile alcohols. From these results, we conclude that functional redundancy and inverse regulation of PedE and PedH represent an adaptive strategy of KT2440 to optimize growth with volatile alcohols in response to the availability of different lanthanides. Because of their low bioavailability, lanthanides have long been considered biologically inert. In recent years, however, the identification of lanthanides as a cofactor in methylotrophic bacteria has attracted tremendous interest among various biological fields. The present study reveals that one of the two PQQ-ADHs produced by the model organism KT2440 also utilizes lanthanides as a cofactor, thus expanding the scope of lanthanide-employing bacteria beyond the methylotrophs. Similar to the system described in methylotrophic bacteria, a complex regulatory network is involved in lanthanide-responsive switching between the two PQQ-ADHs encoded by KT2440. We further show that the functional production of at least one of the enzymes is crucial for efficient growth with several volatile alcohols. Overall, our study provides a novel understanding of the redundancy of PQQ-ADHs observed in many organisms and further highlights the importance of lanthanides for bacterial metabolism, particularly in soil environments.
醇类和醛类的氧化对于多种挥发性有机化合物（VOCs）的解毒和高效分解代谢至关重要。因此，许多革兰氏阴性细菌进化出了基于吡咯喹啉醌依赖性醇脱氢酶（PQQ-ADHs）的周质氧化系统，这些系统通常在功能上是冗余的。在此，我们基于从土壤栖居模式生物KT2440中纯化的酶，首次报道并表征了一种非甲基营养型细菌中依赖镧系元素的PQQ-ADH（PedH）。PedH（PP_2679）对一系列底物表现出酶活性，类似于其依赖钙的对应物PedE（PP_2674），包括直链和芳香族伯醇和仲醇以及醛类，但仅在存在镧系元素离子（包括La、Ce、Pr、Sm或Nd）的情况下。报告基因检测表明，PedH不仅具有催化功能，还参与了 和 的转录调控，很可能作为一个传感模块发挥作用。值得注意的是，潜在的调控网络对低至1至10 nM的镧有反应，该浓度被认为具有生态相关性。本研究进一步证明，PQQ依赖性氧化系统对于利用多种挥发性醇进行高效生长至关重要。从这些结果中，我们得出结论，PedE和PedH的功能冗余和反向调控代表了KT2440的一种适应性策略，以响应不同镧系元素的可用性来优化利用挥发性醇的生长。由于镧系元素的生物利用度低，长期以来它们一直被认为是生物惰性的。然而，近年来，镧系元素作为甲基营养型细菌中的一种辅因子的鉴定在各个生物学领域引起了极大的兴趣。本研究表明，模式生物KT2440产生的两种PQQ-ADHs之一也利用镧系元素作为辅因子，从而将利用镧系元素的细菌范围扩展到甲基营养型细菌之外。与甲基营养型细菌中描述的系统类似，一个复杂的调控网络参与了KT2440编码的两种PQQ-ADHs之间的镧系元素响应切换。我们进一步表明，至少一种酶的功能性产生对于利用几种挥发性醇进行高效生长至关重要。总体而言，我们的研究为许多生物体中观察到的PQQ-ADHs的冗余提供了新的理解，并进一步突出了镧系元素对细菌代谢的重要性，特别是在土壤环境中。
