Identification and characterization of a multidomain hyperthermophilic cellulase from an archaeal enrichment

Abstract

Despite extensive studies on microbial and enzymatic lignocellulose degradation, relatively few Archaea are known to deconstruct crystalline cellulose. Here we describe a consortium of three hyperthermophilic archaea enriched from a continental geothermal source by growth at 90 °C on crystalline cellulose, representing the first instance of Archaea able to deconstruct lignocellulose optimally above 90 °C. Following metagenomic studies on the consortium, a 90 kDa, multidomain cellulase, annotated as a member of the TIm barrel glycosyl hydrolase superfamily, was characterized. The multidomain architecture of this protein is uncommon for hyperthermophilic endoglucanases, and two of the four domains of the enzyme have no characterized homologues. The recombinant enzyme has optimal activity at 109 °C, a halflife of 5 h at 100 °C, and resists denaturation in strong detergents, high-salt concentrations, and ionic liquids. Cellulases active above 100 °C may assist in biofuel production from lignocellulosic feedstocks by hydrolysing cellulose under conditions typically employed in biomass pretreatment.

Metagenomics of microbial and viral life in terrestrial geothermal environments

“…In addition, supernatants of the enriched cultures showed endoglucanase and xylanase activities more stable than those commercially available and exploited in biorefineries. With a similar approach, enrichments of a sample from a 94°C geothermal pool in Nevada (USA) on Miscanthus and cellulose Avicel in strictly anaerobic conditions at 90°C were performed (Graham et al 2011). Three 16S rRNA genes were identified corresponding to the archaea Ignisphaera aggregans, Pyrobaculum islandicum, and Thermophilum pendens, with the Ignisphaera-like strain dominating the microbiome.…”

Recombinant hyperthermophilic enzyme expression in plants: a novel approach for lignocellulose digestion

“…Recombinant T inact values 10-158C > T opt . Details can be found in [63,64,67,68]. Abbreviations: T inact , temperature at which enzyme are 50% inactive; T opt , optimum temperature for activity.…”

“…A large number of hyperthermophilic enzymes capable of hydrolyzing lignocellulosic biomass have been cloned, characterized, and expressed in E. coli and other hosts [60,[62][63][64], but only a few have been successfully expressed in various host plants (Table S1 in the supplementary material online). Comparative lignocellulosic-digestion studies with mesophilic and hyperthermophilic cellulases and hemicellulases have demonstrated that the functionally homologous hyperthermophilic enzymes can increase saccharification yields and shorten incubation times, and may eliminate the risk of downstream contamination by mesophilic microorganisms competing for fermentable sugars [65,66].…”

Biomass Converting Enzymes as Industrial Biocatalysts for Fuels and Chemicals: Recent Developments

“…The exploration of biological diversity, particularly from extremophilic organisms, may reveal new cellulases with improved properties for specific industrial processes. For example, it has been shown that cellulases from halophilic organisms have higher resistance to inactivating ionic liquid residues from certain pretreatments processes [117,118]. Protein engineering of enzymes, such as components of the T. reesei cellulase complex, to improve their suitability for industrial biomass applications has been a growing area of activity within both academic and industrial research into biomass conversion.…”