Abstract:Alkenes, unsaturated hydrocarbons with carbon-carbon double bonds, are emitted in large quantities through both natural and anthropogenic processes. These compounds exhibit diverse functions and characteristics due to variations in their structures. Ethylene, for instance, is a crucial regulator of plant growth, while propylene serves as the primary raw material for the industrial production of polypropylene and acrylonitrile. However, some alkenes pose environmental and health risks. 1,3-butadiene, used in the manufacturing of synthetic rubber and plastics, is a known carcinogen. Isoprene, the most abundant non-methane biogenic volatile organic compound, significantly impacts global climate change. Microorganisms play a critical role in the environmental fate of alkenes by mediating their degradation and transformation. Understanding these microbial processes is essential for elucidating the flow of alkenes in the environment and their impacts on geochemical cycles. Furthermore, this knowledge holds great promise for the bioremediation of alkene-contaminated sites. This paper comprehensively reviews the aerobic and anaerobic microbial degradation and transformation mechanisms of five prevalent short-chain alkenes: ethylene, propylene, butene, 1,3-butadiene, and isoprene. Alkene-degrading strains are widely distributed across multiple phyla. Despite the structural differences among alkenes, their microbial degradation pathways share common features. For example, under oxic conditions, short-chain alkenes are typically oxidized by alkene monooxygenases, the products of which are then conjugated with coenzyme M or glutathione. After a series of enzymatic transformations, they ultimately enter the central metabolic pathways of microorganisms. Under anoxic conditions, short-chain alkenes can be transformed by acetogens, methanogens, and other microorganisms via hydrogenation reactions. By elucidating the mechanisms of microbial degradation and transformation of common short-chain alkenes, this study emphasizes the crucial role of microorganisms in bioremediation efforts at alkene-contaminated sites. Moreover, it contributes to a deeper understanding of microbial influences on geochemical cycles and global climate change, ultimately promoting sustainable development and efficient resource utilization.
