Bacillus licheniformis inoculation promoted humification process for kitchen waste composting: Organic components transformation and bacterial metabolic mechanism

Kitchen waste (KW) composting always has trouble with slow humification process and low humification degree. The objective of this study was to develop potentially efficient solutions to improve the humification of KW composting, accelerate the humus synthesis and produce HS with a high polymerization degree. The impact of Bacillus licheniformis inoculation on the transformation of organic components, humus synthesis, and bacterial metabolic pathways in kitchen waste composting, was investigated. Results revealed that microbial inoculation promoted the degradation of organic constituents, especially readily degradable carbohydrates during the heating phase and lignocellulose fractions during the cooling phase. Inoculation facilitated the production and conversion of polyphenol, reducing sugar, and amino acids, leading to an increase of 20% in the content of humic acid compared to the control. High-throughput sequencing and network analysis indicated inoculation enriched the presence of Bacillus, Lactobacillus, and Streptomyces during the heating phase, while suppressing the abundance of Pseudomonas and Oceanobacillus, enhancing positive microbial interactions. PICRUSt2 analysis suggested inoculation enhanced the metabolism of carbohydrates and amino acids, promoting the polyphenol humification pathway and facilitating the formation of humus. These findings provide insights for optimizing the humification process of kitchen waste composting by microbial inoculation.

Maleic anhydride promotes humus formation via inducing functional enzymes response in composting

The purpose of this paper was to explore the promotion of maleic anhydride on the polymerization of precursors into humus in composting, and analyze the changes of key functional enzymes. The results showed that the content of humus in the treatment group added maleic anhydride (MAH) was higher than that in the control check (CK). The decrease rate of humus precursor concentration of MAH was also higher than that of CK. In MAH, the activities of laccase and tyrosinase were improved, thus enhanced the catalytic conversion of humus precursors. The analysis of bacterial community showed that maleic anhydride optimized the community structure of humification functional enzymes producing bacteria, with the most obvious increase of Firmicutes. In conclusion, this study provided theoretical supports for the introduction of maleic anhydride into the compost system to promote the polymerization of precursors to form humus.

Mechanism analysis of humification coupling metabolic pathways based on cow dung composting with ionic liquids

This study focused on how adding ionic liquids (IL) affects composting humification. During the warming and thermophilic phases, addition of IL increased precursors content, and increased the polymerization of humus (HS) at later stages. Furthermore, the final HS and humic acid (HA) content of experimental groups (T) groups 129.79 mg/g and 79.91 mg/g were higher than in control group (CK) 118.57 mg/g and 74.53 mg/g, respectively (p < 0.05). IL up-regulated the gene abundance of metabolism for carbohydrate and amino acid (AA), and promoted the contributions of Actinobacteria and Proteobacteria, which affected humification. The redundancy analysis (RDA) results showed that the citrate-cycle (TCA cycle)(ko0020), pentose phosphate pathway (ko00030), pyruvate metabolism (ko00620), glyoxylate and dicarboxylate metabolism (ko00630), propanoate metabolism (ko00640), butanoate metabolism (ko00650) positively correlated with HA and HI. HA and humification index (HI) positively correlated with AA metabolic pathways, and fulvic acid (FA) was negatively correlated with these pathways. Overall, metabolism for carbohydrate and AA metabolism favored compost humification. ILs improved metabolism for carbohydrate and amino acid metabolism, thus enhancing humification.

The functions of potential intermediates and fungal communities involved in the humus formation of different materials at the thermophilic phase

Humus is the final product of humus precursors (HPS) during the humification process, while the associated mechanisms of humus formation have not been clarified. Here, the HPS degradation intermediate and core fungal function for wheat straw and chicken manure compost (SCM), cow dung compost (CD), Chinese traditional medicine residue compost (CTM) and mushroom dreg and chicken manure compost (MCM) was investigated during the thermophilic phase. The results showed SCM and MCM were rich in proteins, lipids, cellulose, low-molecular-weight organic acids, while CD and CTM contained abundant carbohydrates, aliphatic compounds, easily biodegradable aromatic structures, and intermediates from the lignocellulose degradation. In particular, the HPS degrading intermediates including O-alkyl-C and aromatic C compounds were the critical factors, and Scedosporium, Hypsizygus and Remersonia were the core fungal genera for the humification. Furthermore, the potential fungal functional genes involved in carbohydrate and lignin degradation might be the key factors to drive the humification process.