Microbial biorefinery approaches are beginning to define renewable and sustainable routes to clean-burning and non-fossil fuel-derived gaseous alkanes (known as ‘bio-LPG’). The most promising strategies have used a terminal fatty acid photodecarboxylase, enabling light-driven propane production from externally fed waste butyric acid. Use of Halomonas (a robust extremophile microbial chassis) with these pathways has enabled bio-LPG production under non-sterile conditions and using waste biomass as the carbon source. Here, we describe new engineering approaches to produce next-generation pathways that use amino acids as fuel precursors for bio-LPG production (propane, butane and isobutane blends). Multiple pathways from the amino acids valine, leucine and isoleucine were designed in E. coli for the production of propane, isobutane and butane, respectively. A branched-chain keto acid decarboxylase-dependent pathway utilising fatty acid photodecarboxylase was the most effective route, generating higher alkane gas titres over alternative routes requiring coenzyme A and/or aldehyde deformylating oxygenase. Isobutane was the major gas produced in standard (mixed amino acid) medium, however valine supplementation led to primarily propane production. Transitioning pathways into Halomonas strain TQ10 enabled fermentative production of mixed alkane gases under non-sterile conditions on simple carbon sources. Chromosomal integration of inducible (~ 180 mg/g cells/day) and constitutive (~ 30 mg/g cells/day) pathways into Halomonas generated production strains shown to be stable for up to 7 days. This study highlights new microbial pathways for the production of clean-burning bio-LPG fuels from amino acids. The use of stable Halomonas production strains could lead to gas production in the field under non-sterile conditions following process optimisation.

中文翻译：

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源自氨基酸的可再生和可调节的生物液化石油气混合物。

微生物生物精炼方法开始定义清洁燃烧和非化石燃料衍生的气态烷烃（称为“生物液化石油气”）的可再生和可持续路线。最有希望的策略是使用末端脂肪酸光脱羧酶，使从外部供给的废丁酸光驱动丙烷生产成为可能。通过这些途径使用卤单胞菌（一种强大的极端微生物底盘）能够在非无菌条件下生产生物液化石油气，并使用废弃生物质作为碳源。在这里，我们描述了新的工程方法来生产使用氨基酸作为燃料前体来生产生物液化石油气（丙烷、丁烷和异丁烷混合物）的下一代途径。在大肠杆菌中设计了来自氨基酸缬氨酸、亮氨酸和异亮氨酸的多种途径，用于生产丙烷、异丁烷和丁烷，分别。利用脂肪酸光脱羧酶的支链酮酸脱羧酶依赖性途径是最有效的途径，与需要辅酶 A 和/或醛去甲酰化加氧酶的替代途径相比，产生更高的烷烃气体滴度。异丁烷是标准（混合氨基酸）培养基中产生的主要气体，但补充缬氨酸导致主要产生丙烷。过渡到 Halomonas 菌株 TQ10 的途径能够在简单碳源的非无菌条件下发酵生产混合烷烃气体。诱导型（~ 180 mg/g 细胞/天）和组成型（~ 30 mg/g 细胞/天）途径进入卤单胞菌的染色体整合产生的生产菌株显示稳定长达 7 天。这项研究强调了从氨基酸生产清洁燃烧的生物液化石油气燃料的新微生物途径。使用稳定的卤单胞菌生产菌株可能会导致在工艺优化后在非无菌条件下在现场生产气体。