Table_5_Aerobic Methoxydotrophy: Growth on Methoxylated Aromatic Compounds by Methylobacteriaceae.XLSX

Pink-pigmented facultative methylotrophs have long been studied for their ability to grow on reduced single-carbon (C1) compounds. The C1 groups that support methylotrophic growth may come from a variety of sources. Here, we describe a group of Methylobacterium strains that can engage in methoxydotrophy: they can metabolize the methoxy groups from several aromatic compounds that are commonly the product of lignin depolymerization. Furthermore, these organisms can utilize the full aromatic ring as a growth substrate, a phenotype that has rarely been described in Methylobacterium. We demonstrated growth on p-hydroxybenzoate, protocatechuate, vanillate, and ferulate in laboratory culture conditions. We also used comparative genomics to explore the evolutionary history of this trait, finding that the capacity for aromatic catabolism is likely ancestral to two clades of Methylobacterium, but has also been acquired horizontally by closely related organisms. In addition, we surveyed the published metagenome data to find that the most abundant group of aromatic-degrading Methylobacterium in the environment is likely the group related to Methylobacterium nodulans, and they are especially common in soil and root environments. The demethoxylation of lignin-derived aromatic monomers in aerobic environments releases formaldehyde, a metabolite that is a potent cellular toxin but that is also a growth substrate for methylotrophs. We found that, whereas some known lignin-degrading organisms excrete formaldehyde as a byproduct during growth on vanillate, Methylobacterium do not. This observation is especially relevant to our understanding of the ecology and the bioengineering of lignin degradation.

粉红着色的兼性甲基营养菌因其能够在单碳（C1）化合物上生长的能力而长期受到研究。支持甲基营养生长的C1基团可能源自多种来源。在此，我们描述了一组能够进行甲氧基营养的甲基杆菌菌株：它们能够代谢从多种芳香化合物中提取的甲氧基团，这些化合物通常是木质素解聚的产物。此外，这些生物体还能够利用完整的芳香环作为生长底物，这种表型在甲基杆菌中鲜有描述。我们在实验室培养条件下证明了这些菌株能够在对羟基苯甲酸、原儿茶酸、香草酸和香草醛上生长。我们还利用比较基因组学方法探究了这一特性的进化历史，发现芳香族代谢的能力可能起源于甲基杆菌的两个类群，但也已被密切相关物种水平地获取。此外，我们调查了已发表的宏基因组数据，发现环境中芳香族降解的甲基杆菌最丰富的群体可能与结瘤甲基杆菌相关，它们在土壤和根际环境中尤为常见。在好氧环境中，木质素衍生的芳香族单体的脱甲氧基化释放出甲醛，这是一种强烈的细胞毒素，但同时也是甲基营养菌的生长底物。我们发现，尽管一些已知的木质素降解生物体在香草酸上生长时将甲醛作为副产物排出，但甲基杆菌则不然。这一观察结果对于我们理解木质素降解的生态学和生物工程具有重要意义。