Core bacterial community driven the conversion of fulvic acid components during composting with adding manganese dioxide.

Here, we revealed the effects of microbes on fulvic acid (FA) formation in composting by adding MnO2. The results showed that the MnO2 promoted the formation of highly humified components (79.2% increased for component 2, and 45.8% increased for component 3) in FA. Additionally, core bacteria involved in FA transformation were identified, the MnO2 increased the relative abundance of core bacteria. Notably, two different core bacteria types were identified: "transforming bacteria" and "processing bacteria". The "transforming bacteria" dominated (about 40% contribution) in the formation of FA components with a high humification degree. The structural equation model confirmed that "transforming bacteria" could convert partly FA components with low humification into highly humified components, and the "transforming bacteria" could be regulated by environmental factors. These findings provided a new insight to manage FA humification degree during composting and helped to improve the application value of FA.