Abstract: Hydrogen (H₂) is a crucial electron and energy carrier in nature. Hydrogen-producing and hydrogen-consuming microorganisms are abundant in the environment, which constitute the microbial hydrogen cycle. Hydrogen cycle includes intraspecific and interspecific hydrogen interchange, drives a variety of microbial processes, and is closely related to the cycling of other elements, such as C, N, and S. Therefore, understanding microbial hydrogen cycling composition and processes has important theoretical significance and practical implications for elucidating the ecological and environmental effects of hydrogen cycling. This review systematically describes the hydrogen-producing and hydrogenconsuming microorganisms, analyzes the processes of hydrogen among microbial communities and associated hydrogen cycle mechanisms, elucidates the ecological and environmental effects of hydrogen cycle from different perspectives, points out the shortcomings of current research, and proposes the key directions for future research.

Key words: hydrogen, microorganism, intraspecific hydrogen cycle, interspecific hydrogen cycle, ecological and environmental effect