A xylan-degrading thermophilic and obligate anaerobe Xylanivirga thermophila gen. nov., sp. nov., isolated from an anammox dominant wastewater treatment plant, and proposal of Xylanivirgaceae fam. nov

Enhancing cellulose acetate biodegradability in cigarette filters: an in-depth analysis of thermal alkaline pretreatment, microbial dynamics, and breakdown pathway prediction

BACKGROUND

The demand for bioplastics has increased exponentially as they have emerged as alternatives to petrochemical plastics. However, there is a substantial lack of knowledge regarding bioplastic degradation. This study developed a novel pretreatment method to improve the accessibility of a bioplastic substrate for biodegradation. In this study, cellulose acetate, a bioplastic found in the world's most littered waste, e.g. cigarette filters, was selected as a potential substrate. Before anaerobic digestion, three thermal alkaline pretreatments: TA 30 °C, TA 90 °C, and TA 121 °C, were used to evaluate their effects on the chemical alterations of cellulose acetate.

RESULT

The ester groups in cellulose acetate were significantly reduced by the TA 30 °C pretreatment, as seen by a decrease in C = O stretching vibrations and shortening of C - O stretches (1,270 ∼ 1,210 cm- 1), indicating effective removal of acetyl groups. This pretreatment significantly enhanced cellulose acetate biodegradability to a maximum of 91%, surpassing the previously reported cellulose acetate degradation. Methane production increased to 695.0 ± 4 mL/g of volatile solid after TA 30 °C pretreatment, indicating enhanced cellulose acetate accessibility to microorganisms, which resulted in superior biogas production compared to the control (306.0 ± 10 mL/g of volatile solid). Diverse microbes in the anaerobic digestion system included hydrolytic (AB240379_g, Acetomicrobium, FN436103_g, etc.), fermentative, and volatile fatty acids degrading bacteria (JF417922_g, AB274492_g, Coprothermobacter, etc.), with Methanobacterium and Methanothermobacter being the sole hydrogenotrophic methanogens in the anaerobic digestion system. Additionally, an attempt to predict the pathway for the effective degradation of cellulose acetate from the microbial community in different pretreatment conditions.

CONCLUSIONS

To the best of our knowledge, this is the first study to estimate the maximum cellulose acetate degradation rate, with a simple and cost-effective pretreatment procedure. This approach holds promise for mitigating the environmental impact of cellulose acetate of cigarette filters and presents a sustainable and economically viable waste management strategy.

Arabinan saccharification by biogas reactor metagenome-derived arabinosyl hydrolases

BACKGROUND

Plant cell walls represent the most plentiful renewable organic resource on earth, but due to their heterogeneity, complex structure and partial recalcitrance, their use as biotechnological feedstock is still limited.

RESULTS

In order to identify efficient enzymes for polysaccharide breakdown, we have carried out functional screening of metagenomic fosmid libraries from biogas fermenter microbial communities grown on sugar beet pulp, an arabinan-rich agricultural residue, or other sources containing microbes that efficiently depolymerize polysaccharides, using CPH (chromogenic polysaccharide hydrogel) or ICB (insoluble chromogenic biomass) labeled polysaccharide substrates. Seventy-one depolymerase-encoding genes were identified from 55 active fosmid clones by using Illumina and Sanger sequencing and dbCAN CAZyme (carbohydrate-active enzyme) annotation. An around 56 kb assembled DNA fragment putatively originating from Xylanivirga thermophila strain or a close relative was analyzed in detail. It contained 48 ORFs (open reading frames), of which 31 were assigned to sugar metabolism. Interestingly, a large number of genes for enzymes putatively involved in degradation and utilization of arabinose-containing carbohydrates were found. Seven putative arabinosyl hydrolases from this DNA fragment belonging to glycoside hydrolase (GH) families GH51 and GH43 were biochemically characterized, revealing two with endo-arabinanase activity and four with exo-α-L-arabinofuranosidase activity but with complementary cleavage properties. These enzymes were found to act synergistically and can completely hydrolyze SBA (sugar beet arabinan) and DA (debranched arabinan).

CONCLUSIONS

We screened 32,776 fosmid clones from several metagenomic libraries with chromogenic lignocellulosic substrates for functional enzymes to advance the understanding about the saccharification of recalcitrant lignocellulose. Seven putative X. thermophila arabinosyl hydrolases were characterized for pectic substrate degradation. The arabinosyl hydrolases displayed maximum activity and significant long-term stability around 50 °C. The enzyme cocktails composed in this study fully degraded the arabinan substrates and thus could serve for arabinose production in food and biofuel industries.