Bayer Travis S, Widmaier Daniel M, Temme Karsten, Mirsky Ethan A, Santi Daniel V, Voigt Christopher A
Department of Pharmaceutical Chemistry, University of California, San Francisco, MC 2540, Room 408C, 1700 4th Street, San Francisco, California 94158-2330, USA.
J Am Chem Soc. 2009 May 13;131(18):6508-15. doi: 10.1021/ja809461u.
Methyl halides are used as agricultural fumigants and are precursor molecules that can be catalytically converted to chemicals and fuels. Plants and microorganisms naturally produce methyl halides, but these organisms produce very low yields or are not amenable to industrial production. A single methyl halide transferase (MHT) enzyme transfers the methyl group from the ubiquitous metabolite S-adenoyl methionine (SAM) to a halide ion. Using a synthetic metagenomic approach, we chemically synthesized all 89 putative MHT genes from plants, fungi, bacteria, and unidentified organisms present in the NCBI sequence database. The set was screened in Escherichia coli to identify the rates of CH(3)Cl, CH(3)Br, and CH(3)I production, with 56% of the library active on chloride, 85% on bromide, and 69% on iodide. Expression of the highest activity MHT and subsequent engineering in Saccharomyces cerevisiae results in productivity of 190 mg/L-h from glucose and sucrose. Using a symbiotic co-culture of the engineered yeast and the cellulolytic bacterium Actinotalea fermentans, we are able to achieve methyl halide production from unprocessed switchgrass (Panicum virgatum), corn stover, sugar cane bagasse, and poplar (Populus sp.). These results demonstrate the potential of producing methyl halides from non-food agricultural resources.
甲基卤化物用作农业熏蒸剂，并且是可通过催化转化为化学品和燃料的前体分子。植物和微生物天然会产生甲基卤化物，但这些生物体的产量非常低或不适合工业化生产。单个甲基卤化物转移酶（MHT）可将普遍存在的代谢物S-腺苷甲硫氨酸（SAM）中的甲基转移至卤离子。我们采用合成宏基因组学方法，从NCBI序列数据库中存在的植物、真菌、细菌及未鉴定生物体中化学合成了所有89个推定的MHT基因。在大肠杆菌中对该基因集进行筛选，以确定CH(3)Cl、CH(3)Br和CH(3)I的生成速率，该文库中56%的基因对氯化物有活性，85%对溴化物有活性，69%对碘化物有活性。最高活性MHT的表达以及随后在酿酒酵母中的工程改造，可使葡萄糖和蔗糖的产量达到190 mg/L-h。利用工程酵母与纤维素分解细菌发酵单孢放线菌的共生共培养，我们能够从未加工的柳枝稷（Panicum virgatum）、玉米秸秆、甘蔗渣和杨树（Populus sp.）中生产甲基卤化物。这些结果证明了利用非粮食农业资源生产甲基卤化物的潜力。
