Thermophilic microbial cellulose decomposition and methanogenesis pathways recharacterized by metatranscriptomic and metagenomic analysis

Abstract

The metatranscriptomic recharacterization in the present study captured microbial enzymes at the unprecedented scale of 40,000 active genes belonged to 2,269 KEGG functions were identified. The novel information obtained herein revealed interesting patterns and provides an initial transcriptional insight into the thermophilic cellulose methanization process. Synergistic beta-sugar consumption by Thermotogales is crucial for cellulose hydrolysis in the thermophilic cellulose-degrading consortium because the primary cellulose degraders Clostridiales showed metabolic incompetence in subsequent beta-sugar pathways. Additionally, comparable transcription of putative Sus-like polysaccharide utilization loci (PULs) was observed in an unclassified order of Bacteroidetes suggesting the importance of PULs mechanism for polysaccharides breakdown in thermophilic systems. Despite the abundance of acetate as a fermentation product, the acetate-utilizing Methanosarcinales were less prevalent by 60% than the hydrogenotrophic Methanobacteriales. Whereas the aceticlastic methanogenesis pathway was markedly more active in terms of transcriptional activities in key genes, indicating that the less dominant Methanosarcinales are more active than their hydrogenotrophic counterparts in methane metabolism. These findings suggest that the minority of aceticlastic methanogens are not necessarily associated with repressed metabolism, in a pattern that was commonly observed in the cellulose-based methanization consortium, and thus challenge the causal likelihood proposed by previous studies.

Long-Term Enrichment on Cellulose or Xylan Causes Functional and Taxonomic Convergence of Microbial Communities from Anaerobic Digesters

“…1). Experimentally maintaining a pH of 6.0 and glucose supplementation allowed the continuous thermophilic digestion of cellulose with an SWH inoculum for over a year (44). These results suggest that the success of thermophilic cellulose digestions with or without a cosubstrate is sensitive to both pH and inoculum composition.…”

Application of Metagenomics in Environmental Anaerobic Technology

“…Later, the rapidly decreasing sequencing cost and the prevalence of NGS technologies other than 454 pyrosequencing allowed for more extensive applications of HTS-based metagenomics approaches, including 16S rRNA gene amplicons sequencing and metagenome for novel microbial insights into the anaerobic digestion processes operated for bioenergy production (e.g., methane, biohydrogen, bioethanol, fatty acids) and/or pollution control (e.g., refractory compounds, bacterial pathogens, antibiotics resistance genes). A few pioneering studies even applied metatranscriptome (Xia et al 2014;Zakrzewski et al 2012) or metaproteome (Lü et al 2013;Kohrs et al 2013;Hanreich et al 2013;Hanreich et al 2012;Abram et al 2011;Heyer et al 2013;Wu et al 2013) to gain some preliminary insights into the gene expression and active enzymes in anaerobic digestion processes.…”

“…However, so far, little work has been done from this aspect. Only until quite recently, Xia et al (2014) used metatranscriptomic and metagenomic approaches to re-characterize microbial cellulose anaerobic degradation and methanogenesis pathways in a lab-scale thermophilic cellulose-degrading reactor. They discovered that although genes involved in methanogenesis by aceticlastic order Methanosarcinales were less prevalent than hydrogenotrophic order Methanobacteriales (by 60%), the transcriptional activities of Methanosarcinales were remarkably higher (six times) than Methanobacteriales.…”

“…In another metagenomics-based study, Xia et al (2014) initially used coupled metatranscriptome and metagenome to gain novel insights into the thermophilic cellulose methanization process. By screening an unprecedented number of active genes (up to 40,000), the authors discovered for the first time the co-transcription of hemicellulases by Clostridiales and Spirochaetales in the presence of cellulose stimulation alone, the comparable transcription of Sus-like polysaccharide utilization loci for polysaccharides breakdown by an unclassified order of Bacteroidetes, as well as the significant role of Thermotogales in synergistic beta-sugar consumption so as to make up for the inadequacies of cellulose degrader Clostridiale in metabolizing this substrate.…”

Applications of cellulose nanomaterials in pharmaceutical science and pharmacology

“…The vast abundance and renewability of cellulose make it an 'almost inexhaustible' [2,3] material. It has been widely claimed by numerous researchers as the most abundant renewable biopolymer [4], natural polymer [5,6], natural organic bio material [7], biomass [8], biopolymer [9,10], natural polysaccharide [11], and renewable natural biopolymer [12]. Other prominent attributes of cellulose include multifunctionality [13], chemical stability and derivatizability [5], lightweight, high aspect ratio, excellent mechanical properties, low density, low coefficient of thermal expansion, functionalizable surface, and carbon neutrality [9].…”