Abstract:

Methane has been considered as a potential carbon source in industrial biotechnology because of its abundance, sustainability, high reducibility, and microbial availability. The biological conversion of methane into chemicals or fuels does not only reduce greenhouse gas emissions, but also substitute food-based substrates used in bio-manufacturing. Methanotrophs are gram-negative bacteria, and most are isolated from methane-plentiful environments. Owing to the presence of the methane monooxygenase, methanotrophs constitute a unique group of microbes. As an important industrially-promising microorganism with the characteristics of robust and anti-contamination ability, methanotrophs capable of growing with methane as the sole energy and carbon source play a significant role in carbon-neutral society by replacing petroleum-based products with biosynthesized products. Therefore, studies on methanotrophs for the biological conversion of methane have attracted extensive attention in recent years. With the rapid development of genetic manipulations tools and strategies for metabolically-engineered methanotrophs construction, including gene editing methods, regulation of metabolic pathways, and bio-elements mining, methanotrophic cell factories have been employed to efficiently convert methane into a variety of bulk chemicals and biofuels. In this review, biosynthetic technologies related to bioconversion of under-utilized methane ranging from fundamental understanding, systematic analysis, metabolic engineering to bio-product production are introduced. The genetic manipulations tools of methanotrophs, the approaches of methanotrophic cell factory construction, and the enhancement of methane assimilation efficiency are summarized from the aspects including the research progress of genetic engineering of methanotrophs, the regulation of methane carbon flux, the overexpression of heterologous pathway genes, and the accumulation of metabolic intermediates. Besides, the applications of genomics, transcriptomics, metabolomics, and metabolic modeling have been also deployed to facilitate the methane metabolism in methanotrophs chassis. Finally, given the strategy of 'waste-to-value' production, the challenges and opportunities for methane bioconversion by methanotrophs are also discussed and prospected based on industrial applications in terms of the research progress in the biosynthesis of methane-based acids, terpenes, alcohols, and other chemicals.

Key words: methane, methanotrophs, cell factory, construction strategy, chemical biosynthesis

摘要：

由于来源广泛且储量丰富，甲烷被认为是极具应用潜力的下一代生物碳源。嗜甲烷菌是一种分离自富含甲烷环境中的革兰氏阴性细菌，其体内含有独特的甲烷单加氧酶能够让这类微生物以甲烷为唯一碳源和能源进行生长、代谢与产物合成。作为一种重要的工业微生物，嗜甲烷菌在甲烷生物转化利用、温室气体减排和“碳中和”策略开发方面具有重要意义。近年来，随着嗜甲烷菌基因编辑方法、代谢路径调控、生物元件挖掘等菌种构建工具和策略的不断开发，嗜甲烷菌人工细胞可高效转化甲烷生物合成多种大宗化学品和生物燃料。本文围绕遗传改造工具、甲烷碳流调控、异源途径表达和代谢节点累积等方面的研究进展，概述了构建嗜甲烷菌人工细胞的方法和提高甲烷同化效率的策略。同时介绍了基因组学、转录组学、代谢组学等组学研究方法在调控嗜甲烷菌底盘碳代谢流向和通量中的应用。最后，结合生物转化甲烷合成酸类、萜类、醇类等化学品的研究，分析并展望了嗜甲烷菌工业化应用所面临的挑战和机遇。

关键词: 甲烷, 嗜甲烷菌, 细胞工厂, 构建策略, 化学品生物合成