Characterization of hemicellulase and cellulase from the extremely thermophilic bacterium Caldicellulosiruptor owensensis and their potential application for bioconversion of lignocellulosic biomass without pretreatment

Abstract

BackgroundPretreatment is currently the common approach for improving the efficiency of enzymatic hydrolysis on lignocellulose. However, the pretreatment process is expensive and will produce inhibitors such as furan derivatives and phenol derivatives. If the lignocellulosic biomass can efficiently be saccharified by enzymolysis without pretreatment, the bioconversion process would be simplified. The genus Caldicellulosiruptor, an obligatory anaerobic and extreme thermophile can produce a diverse set of glycoside hydrolases (GHs) for deconstruction of lignocellulosic biomass. It gives potential opportunities for improving the efficiency of converting native lignocellulosic biomass to fermentable sugars.ResultsBoth of the extracellular (extra-) and intracellular (intra-) enzymes of C. owensensis cultivated on corncob xylan or xylose had cellulase (including endoglucanase, cellobiohydrolase and β-glucosidase) and hemicellulase (including xylanase, xylosidase, arabinofuranosidase and acetyl xylan esterase) activities. The enzymes of C. owensensis had high ability for degrading hemicellulose of native corn stover and corncob with the conversion rates of xylan 16.7 % and araban 60.0 %. Moreover, they had remarkable synergetic function with the commercial enzyme cocktail Cellic CTec2 (Novoyzmes). When the native corn stover and corncob were respectively, sequentially hydrolyzed by the extra-enzymes of C. owensensis and CTec2, the glucan conversion rates were 31.2 and 37.9 %,which were 1.7- and 1.9-fold of each control (hydrolyzed by CTec2 alone), whereas the glucan conversion rates of the steam-exploded corn stover and corncob hydrolyzed by CTec2 alone on the same loading rate were 38.2 and 39.6 %, respectively. These results show that hydrolysis by the extra-enzyme of C. owensensis made almost the same contribution as steam-exploded pretreatment on degradation of native lignocellulosic biomass. A new process for saccharification of lignocellulosic biomass by sequential hydrolysis is demonstrated in the present research, namely hyperthermal enzymolysis (70–80 °C) by enzymes of C. owensensis followed with mesothermal enzymolysis (50–55 °C) by commercial cellulase. This process has the advantages of no sugar loss, few inhibitors generation and consolidated with sterilization.ConclusionsThe enzymes of C. owensensis demonstrated an enhanced ability to degrade the hemicellulose of native lignocellulose. The pretreatment and detoxification steps may be removed from the bioconversion process of the lignocellulosic biomass by using the enzymes from C. owensensis.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-015-0313-0) contains supplementary material, which is available to authorized users.

Phylogeny, classification and metagenomic bioprospecting of microbial acetyl xylan esterases

“…A range of environments containing a diversity of lignocellulose-degrading organisms, such as forest soils, termite guts, animal rumens and compost have yielded a range of AcXE-expressing organisms, including the fungal species Aspergillus [58,59], Anoxybacillus [76], Trichoderma [98], Orpinomyces [43], Penicillium [57], Schizophyllum [98], Fusarium [99], Coprinopsis [100], Rhodotorula [41] and Neocallimastix [63] and bacteria such as Bacillus [101], Butyrivibrio [102], Caldicellulosiruptor [103], Caldocellum [104], Clostridium [72],…”

“…[133,134], are popular targets for bioprospecting on the basis that their gene products are very likely to be adapted to function optimally under the specific extreme conditions [135][136][137]. A number of AcXEs have been identified from thermophiles and hyperthermophiles, including Caldicellulosiruptor owensensis [103], Thermomonospora fusca [138], Thermoanaerobacterium sp. [106], Thermobifida fusca [107,120], Thermotoga maritima [90], Talaromyces emersonii [139] and Geobacillus stearothermophilus [21].…”

“…No single pre-treatment method can be considered to be ideal for deacetylation of xylans. A recent analysis of the possible role of AcXEs in the bioconversion of lignocellulosic substrates without pre-treatment steps suggests an increased future focus on this enzyme class [103].…”

Microbial diversity of thermophiles with biomass deconstruction potential in a foliage‐rich hot spring

“…(Currie et al., ) are known for decomposing biomass at high temperatures (Bhalla, Bansal, Kumar, Bischoff, & Sani, ). Furthermore, members of the genera Thermotoga (Yu et al., ), Rhodothermus (Keshk, ), Anoxybacillus (Chan et al., ), Rhodothermaceae strain RA (Goh et al., ), and Caldicellulosiruptor (Peng et al., ) were found to produce thermostable enzymes for biomass saccharification.…”

Sequential processing with fermentative Caldicellulosiruptor kronotskyensis and chemolithoautotrophic Cupriavidus necator for converting rice straw and CO2 to polyhydroxybutyrate

“…Extremely thermophile anaerobic bacteria in the genus Caldicellulosiruptor can degrade unpretreated lignocellulosic biomass (Blumer‐Schuette et al, ;; Blumer‐Schuette, Lewis, & Kelly, ; Brunecky et al, ; Peng et al, ). For example, Caldicellulosiruptor bescii simultaneously solubilized cellulose, hemicellulose, and lignin from unpretreated switchgrass by anaerobic fermentation at 78 °C (Kataeva et al, ).…”