Institute of Biodiversity, Aquatic Geomicrobiology, Friedrich Schiller University, Jena, Germany.
Electron Microscopy Center, Jena University Hospital, Jena, Germany.
Appl Environ Microbiol. 2021 Jun 11;87(13):e0314420. doi: 10.1128/AEM.03144-20.
Recent work with Methylorubrum extorquens AM1 identified intracellular, cytoplasmic lanthanide storage in an organism that harnesses these metals for its metabolism. Here, we describe the extracellular and intracellular accumulation of lanthanides in the bacterium RH AL1, a newly isolated and recently characterized methylotroph. Using ultrathin-section transmission electron microscopy (TEM), freeze fracture TEM (FFTEM), and energy-dispersive X-ray spectroscopy, we demonstrated that strain RH AL1 accumulates lanthanides extracellularly at outer membrane vesicles (OMVs) and stores them in the periplasm. High-resolution elemental analyses of biomass samples revealed that strain RH AL1 can accumulate ions of different lanthanide species, with a preference for heavier lanthanides. Its methanol oxidation machinery is supposedly adapted to light lanthanides, and their selective uptake is mediated by dedicated uptake mechanisms. Based on transcriptome sequencing (RNA-seq) analysis, these presumably include the previously characterized TonB-ABC transport system encoded by the cluster but potentially also a type VI secretion system. A high level of constitutive expression of genes coding for lanthanide-dependent enzymes suggested that strain RH AL1 maintains a stable transcript pool to flexibly respond to changing lanthanide availability. Genes coding for lanthanide-dependent enzymes are broadly distributed taxonomically. Our results support the hypothesis that central aspects of lanthanide-dependent metabolism partially differ between the various taxa. Although multiple pieces of evidence have been added to the puzzle of lanthanide-dependent metabolism, we are still far from understanding the physiological role of lanthanides. Given how widespread lanthanide-dependent enzymes are, only limited information is available with respect to how lanthanides are taken up and stored in an organism. Our research complements work with commonly studied model organisms and showed the localized storage of lanthanides in the periplasm. This storage occurred at comparably low concentrations. Strain RH AL1 is able to accumulate lanthanide ions extracellularly and to selectively utilize lighter lanthanides. The bacterium RH AL1 might be an attractive target for developing biorecovery strategies to obtain these economically highly demanded metals in environmentally friendly ways.
最近对甲基盐单胞菌 AM1 的研究发现，一种利用这些金属进行代谢的生物体在细胞质中有内在的、细胞质内的镧系元素储存。在这里，我们描述了新分离并最近表征的甲基营养菌 RH AL1 中细菌外和细胞内镧系元素的积累。使用超薄切片透射电子显微镜（TEM）、冷冻断裂 TEM（FFTEM）和能量色散 X 射线光谱，我们证明了 RH AL1 菌株在外膜囊泡（OMVs）中积累镧系元素并将其储存在周质中。生物质样品的高分辨率元素分析表明，RH AL1 菌株可以积累不同镧系元素的离子，并且偏爱较重的镧系元素。其甲醇氧化机制据称适应于轻镧系元素，并且它们的选择性摄取由专门的摄取机制介导。基于转录组测序（RNA-seq）分析，这些机制可能包括以前由 簇编码的、表征的 TonB-ABC 转运系统，但也可能包括一种类型 VI 分泌系统。编码镧系元素依赖酶的基因的高水平组成型表达表明，RH AL1 菌株维持稳定的转录池，以灵活响应不断变化的镧系元素可用性。编码镧系元素依赖酶的基因在分类上广泛分布。我们的结果支持这样的假设，即镧系元素依赖代谢的核心方面在不同的分类群之间部分不同。尽管已经有越来越多的证据加入到镧系元素依赖代谢的谜题中，但我们仍然远未了解镧系元素的生理作用。鉴于镧系元素依赖酶的广泛分布，关于镧系元素在生物体中的摄取和储存方式，只有有限的信息可用。我们的研究补充了对常见研究模型生物的研究，并显示了镧系元素在周质中的局部储存。这种储存发生在相对较低的浓度下。RH AL1 菌株能够在外细胞中积累镧系离子，并选择性地利用较轻的镧系元素。细菌 RH AL1 可能是开发生物回收策略的有吸引力的目标，以环保的方式获得这些在经济上高度需求的金属。
