Microbial community structure and the function of the hemicellulolytic microbial consortium HMC

Hemicellulose has been one of the indispensable biomass sources within plant cell walls. The vital components such as xylan and glucomannan can render a pivotal hemicellulosic reservoir. The heterogeneous structure and stability of corn cobs can benefit from their lignocellulosic network resistant to effective deconstruction in their natural state, resulting in frequent resource wastage. Additionally, the widespread combustion of corn cobs in the past has led to environmental pollution in the emission of pollutants. In contrast to most natural lignocellulosic materials with low hemicellulose content, corn cobs exhibit a higher hemicellulose content. Moreover, alkali treatment can be used to remove most soluble and lignin components from lignocellulose, thereby increasing the relative hemicellulose content. Therefore, this study focused primarily on the relevance of the hemicellulolytic microbial consortium (HMC) to degrade the hemicellulose backbone xylan. The high-throughput sequence and bioinformatic analysis were made to identify the community structure of HMC. The carbohydrate-active enzymes and KEGG (kyoto encyclopedia of genes and genomes) metabolic pathways were examined to be involved in xylan degradation. High-throughput sequencing of 16S rDNA revealed that the complex microbial community structure of HMC included a diverse range of extremophilic microorganisms in the hemicellulose degradation, such as Tepidimicrobium (18.70%), Aeribacillus (13.50%), and Geobacillus (9.44%). Metagenomics analysis showed that there was a diverse array of carbohydrate enzymes (CAZymes) in the HMC metagenome, covering essential enzyme families, such as AA (auxiliary activities), CBM (carbohydrate-binding modules), CE (carbohydrate esterases), GH (glycoside hydrolases), GT (glycosyl transferases), PL (polysaccharide lyases), and SLH (cellulosome coudles). This diversity underscored the significant potential for carbohydrate degradation, particularly in hemicellulose decomposition. There was a diversity in the metabolically, both the primary and secondary KEGG metabolic networks of HMC. The secondary KEGG metabolic pathways shared the various intracellular metabolic processes, including energy generation and utilization, organic molecule synthesis, and degradation. These pathways involved the carbohydrate, lipid, amino acid, nucleotide, energy, coenzyme, and vitamin metabolism, indicating the complex KEGG metabolic networks. Within the KEGG subpathways, HMC harbored a variety of carbohydrate metabolism pathways and downstream functional enzymes associated with xylan metabolism, including formate, lactate, and acetate production. Additionally, corn cobs and the hemicellulose backbone served as degradation substrates. Their lignocellulosic composition was determined using the Van Soest detergent. Furthermore, the hemicellulose content of corn cobs was quantified, where the content of natural corn cob hemicellulose was estimated at approximately 44%. Moreover, the 5% ammonia treatment showed that there was a significant increase in the relative hemicellulose content of corn cobs in the following treatment. The results indicate that the HMC effectively degraded the xylan and corn cobs within 7 days, with an 80% degradation rate. HMC had produced high-value products, such as reducing sugars (the maximum concentrations were 1.30 mg/mL) and VFAs (volatile fatty acids) during degradation. These volatile fatty acids included formic acid, lactic acid, and acetic acid, with the maximum accumulation concentrations of 0.50, 1.19, and 1.23 mg/mL. Additionally, HMC exhibited significant dynamic changes during xylan degradation. Xylanase activity remained relatively stable in the early stages of cultivation, but significantly increased later, especially reaching the peak on the 7th day. HMC had gradually degraded the xylan to strengthen over time. The activity of carboxymethyl cellulase sodium decreased in a relatively low degradation of carboxymethyl cellulose by HMC. A shift was found in the lignocellulosic components during later stages. Moreover, there were significant dynamic responses in the xylan degradation rate, free protein content, reducing sugars, and volatile fatty acids. In the corn cobs that were treated with 5% ammonia, there was a significant enhancement in the HMC degradation and the production of reducing sugars and volatile fatty acids, where the concentration reached up to 3.54 mg/mL. This finding can provide a deep understanding of the degradation of corn cob hemicellulose using the HMC application. A scientific basis was also offered to efficiently utilize biomass resources during biodegradation. Additionally, theoretical support can be obtained to apply the HMC in bioenergy production and waste degradation, particularly in the sustainable development of biomass resources and strategic management of agricultural waste in the future.