Metagenomic analysis reveals metabolic mechanism of enhancing lignocellulosic anaerobic digestion mediated by CO2/O2-nanobubble water.

[Display omitted] • CO 2 nanobubble water (NW) and O 2 NW increased the methane yields by 6.9% and 18.3%. • Using NW increased the electron transport system and coenzyme F 420 activities. • The key enzymes in the acidification stage were promoted with the addition of NW. • CO 2 NW enhanced genes expression of HM, while O 2 NW stimulated both AM and HM. • O 2 NW upregulated energy metabolism expression, resulting in more ATP production. Nanobubble water (NW) has been reported to enhance anaerobic digestion (AD), but its influence on the metabolic pathways of microorganisms remains unclear. In this study, the specific methane yields of rice straw in the CO 2 NW and O 2 NW treatments increased by 6.9% and 18.3%, respectively. The electron transport system (ETS) and coenzyme F 420 activities were enhanced by the addition of NW. Metagenomic analysis showed that the abundances of most enzymes in the acidification were significantly increased by both CO 2 NW and O 2 NW. Regarding methanogenesis, CO 2 NW promoted the expression of genes encoding enzymes of hydrogenotrophic methanogenesis, while O 2 NW stimulated both the acetoclastic and hydrogenotrophic methanogenesis. With the addition of O 2 NW, the expressions of modules related to the tricarboxylic acid (TCA) cycle and oxidative phosphorylation were enhanced, resulting in increased ATP production. This study provided fundamental evidence of the metabolic pathways of microorganisms mediated by NW at each stage of AD. [ABSTRACT FROM AUTHOR]